SYNTHESIS, FABRICATION, CHARACTERIZATION, …ii ROHIT KUMAR H. VORA Degree: Doctor of Philosophy (PhD), 1998-2003. Department: Chemistry PhD Thesis Title: Synthesis, Fabrication, Characterization,

i

SYNTHESIS, FABRICATION, CHARACTERIZATION,

PROPERTIES AND THERMAL DEGRADATION

KINETICS STUDY OF LOW-K POLY(ETHER IMIDE)S

AND CO-POLY(ETHER IMIDE)S, AND POLY(ETHER

IMIDE)/MMT CLAY NANOCOMPOSITES.

ROHITKUMAR H. VORA

[M.S. (Polym. Sci. & Eng.), Polytechnic Institute of New York, USA (1980)]

A DISSERTATION SUBMITTED

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMISTRY

FACULTY OF SCIENCE

NATIONAL UNIVERSITY OF SINGAPORE

2003

ii

ROHIT KUMAR H. VORA Degree: Doctor of Philosophy (PhD), 1998-2003. Department: Chemistry PhD Thesis Title: Synthesis, Fabrication, Characterization, Properties, and Thermal

Degradation Kinetics Study of Low-K Poly(ether imide)s, Copoly(ether imide)s, and

Poly(ether imide)/MMT Clay Nanocomposites.

ABSTRACT

The objective of the PhD thesis research was the synthesis, film fabrication, characterization, and

structure properties study of series of partially fluorinated poly(ether imide) (6F-PEI),

copoly(ether imide)s (6F-CoPEI) and (6F-PEI)/organosoluble MMT clay nanocomposite from

commercially available monomers and materials. The approach involved the polymerization of

2,2’-bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) with a variety of di-ether-

containing (non-fluorinated) diamines: 4,4-bis(3-aminophenoxy)diphenyl sulfone (m-SED), 4,4-

bis(4-aminophenoxy)diphenyl sulfone (p-SED), and 4,4-bis(4-aminophenoxy)diphenyl propane

(BPADE). The films of these melt processable (6F-PEI) and (6F-CoPEI) polymers from p-SED

and BPADE having trifluoromethyl groups showed excellent electrical properties. Fluoro-

poly(ether imide)s [6FDA + p-SED] and [6FDA + BPADE] had dielectric constants (ε’) of 2.74

and 2.65 at 10MHz respectively. Mathematical model equations were developed to estimate the

dielectric constant (ε’co) of copolyimides. For the copoly(ether imide)s, the dielectric constant

values were in the range between 3.05 to 3.10 at 1 kHz. These values are lower than the

commercially available poly(ether imide) ULTEM1000 (ε’=3.15), and polyimide KaptonH

films (ε’=3.5) at 1 kHz. In addition, (6F-PEI)s, (6F-CoPEI)s, and nanocomposite films not only

showed extraordinary long-term thermo-oxidative stability (TOS), but also exhibited excellent

reduced water absorption relative to commercial polyimides. The transparencies of polymer films

were in the range between 80-90% at 500nm solar wavelength. The nanocomposites showed

excellent solvent resistance, increased glass transition (Tg) values with increasing clay content, a

sharp lowering of the coefficient of thermal expansion (CTE), and improved surface energy.

Keywords: Fluoro-poly(ether imide), Fluoro-copoly(ether imide), Fluoro-poly(ether imide)/MMT clay nanocomposites, Low-dielectric, Estimation of dielectric constant, Thermal degradation kinetics, Thermo-oxidative stability, Surface properties.

ii

DEDICATION

“We measure ourselves by many standards. Our strengths and our intelligence, our wealth and even our good luck, are things which warm our heart and make us feel ourselves a match for life. But deeper than all such things and able to suffice unto itself without them is the sense of the amount of effort we can put forth…. He who can make none is but a shadow; he who can make much is a hero.”

-Prof. William James [A prominent American psychologist of the 19th century (1898).]

I would like to dedicate this dissertation to my beautiful wife, Neela R. Vora, who is

my better half and a very good friend, and to my two extraordinarily special teenage

children, son Ashish and daughter Amee, for their all-out encouragement, support, and

unconditional love during the course of this long research. They are my heroes, who

patiently and lovingly accepted my long and late hours at work at the Institute of

Materials Research and Engineering (IMRE)’s laboratory during those years, at which

time, I almost became a weekend husband and father, but never did they ever fail to let

me know that they loved me. I owe them my deepest gratitude and thanks from the

bottom of my heart. I love you, guys.

iii

ACKNOWLEDGEMENTS

“Mind is a terrible thing to waste” -Rev. Martin Luther King, Jr.

“Poverty is the greatest form of ‘Violence and Sin’ of mankind”

-Mahatma Gandhi I would like to express my sincere appreciation and profound gratitude to my doctoral thesis

advisor, distinguished Professor Suat Hong Goh at the Dept. of Chemistry for his time, resources

support, valuable guidance and mentorship throughout my graduate studies, and also to my co-

advisor Prof. Tai-Shung (Neal) Chung, for allowing me a complete creative freedom in deciding

my thesis research topic and objectives, and for his continuing encouragement.

I would like to express my heartfelt thanks to the President of the National University of

Singapore, Prof. Fong Choon Shih, then the founding director of the Institute of Materials

Research and Engineering (IMRE) for giving me his permission in 1998 to enroll for PhD studies

at the Dept. of Chemistry at NUS, and for also allowing me to carry out a simultaneous PhD

research work at IMRE in the Advanced Polymers Group’s lab while working at IMRE.

I would also like to thank distinguished professor emeritus Prof. Huang Hsing Hua for his

willingness to accept me as his PhD student and, also to allow me to use his laboratory at S9-03-

03 at the Dept. of Chemistry during the early years (1997-1999) of IMRE.

With the blessings of these wonderful teachers and mentors, I initiated my PhD thesis research

work in November 1998 at IMRE. During the last five years, their patience and helpful

suggestions have kept me going in carrying out sustained vigorous research work, because of

which I was successfully able to meet the objectives of my thesis.

I would like to acknowledge and sincerely thank Dr. Motonori Takeda, Senior Managing

Director and Chief Technical Officer of Wakayama Seika Kogyo Co. Ltd., Japan for his

friendship, and for providing various diether-containing diamine monomers free of charge for my

research work. I also would like to thank the wonderful staff of the Advanced Polymers and

Chemicals Cluster at IMRE for many meaningful discussions on analytical techniques.

I must not forget to thank Prof. Syamal K. Lahiri of IMRE, Assoc. Prof. B. V. R. Chowdari of

the Dept. of Physics, Assoc. Prof. Jagdese J. Vittal of the Dept. of Chemistry, Assoc. Prof.

Madapusi P. Srinivasan and Assoc. Prof. Ajay Kumar Ray from the Dept of Chemical &

Environmental Engineering and Assoc. Prof. L. C. Lim from Dept. of Mechanical Engineering.

for their friendship and intellectually stimulating discussions and moral support.

I would also like to thank Prof. Neal Chung and Prof. En-Tang Kang of the Dept of Chemical

& Environmental Engineering for the research collaborations and allowing me to co-supervise

their PhD students, who used my fluoro-polyimides in their research work. Similarly, I would

also like to thank Prof. Michael Philpott, the Head of Dept. Materials Science for inviting me last

iv

year to teach a 2nd year undergraduate level module ‘Polymeric Engineering Materials’ in his

department, thus giving me a unique opportunity to provide manpower training, and have real

experience and feel for an academic teaching, which I enjoyed very much, and at the same time I

was able concentrate on writing this thesis.

In addition, I would like to take this opportunity to thank several of my colleagues and

wonderful friends at IMRE: Dr. Ramam Akkipeddi, Dr. Wang Huimin, Mr. Subramanian

Veeramani, Dr. P. Santhana Gopala Krishnan, Dr. Pramoda Kumari Pallathadka, Dr. Liu Song

Lin, Mr. Sunil Bhangale, Mr. Suresh Kumar Donthu, Mr. Mithilesh Shah, and also to Mr.

Rajamani Lakshminarayanan, Mr. Chinnappan Baskar, Mr. Vetrichelvan Muthalagu, Mr.

Venkataramanan Balasubramaniam, Mr. Goh Ho Wee, Mr. Li Xuedong from the Dept. of

Chemistry; Dr Prashant D. Sawant and Mr. Siddharth Joshi from the Dept. of Physics; Dr. Igor

Goliney, Dr. Rengaswamy Jayaganthan, Dr. Santhiagu Ezhilvalavn from the Dept. of Materials

Science, for sharing their ideas and for their valuable friendship. Working and/or socializing with

all of them has always been a special privilege for me for all these years.

I would like to acknowledge the National University of Singapore for sponsoring my trip to

attend and present an invited technical paper, and to chair a session at the 6th European Technical

Symposium on Polyimides and High Performance Functional Polymers (STEPI-6), held in

Montpellier (FRANCE), during May 13-15, 2002.

Last, but not least, I would like to thank my dear and loving mother Mrs. Hiralaxmi H. Vora,

who taught me how to read, and to my 77 year old dear father, Mr. Harkisondas A. Vora, a

Chemical Engineer (from the UDCT-Bombay University, INDIA) and a very successful

technopreneur and businessman, who got me interested in the subject of science at an early age. I

also thank my dear brother Mayur H. Vora, and sisters Mrs. Chhaya Acharya, Late Mrs. Maya

Parikh, and Mrs. Jayshree Doshi. Also thank my respected parent-in-laws: Late Mrs. Ramabahen

B. Kanakia and Mr. Babubhai M. Kanakia, brother-in-laws: Rashesh B. Kanakia and his wife

Mrs. Rupal Kanakia, and Himanshu B. Kanakia and his wife Mrs. Hiral Kanakia, sister-in-laws:

Mrs. Meena Muni, Mrs. Asha Shah and Mrs. Manisha Vora, and my family for their continual

loving support, and understanding and prayers.

Finally, remembering last three lines from the last stanza of the all-time masterpiece poem

‘Stopping by the woods on a snowy evening’ by the great American poet:

“ But I have promises to keep, And miles to go before I sleep, And miles to go before I sleep.”

-Robert Frost

I am happy to state that my journey for higher learning will not end with getting a PhD degree, as

I truly believe that learning is a life long process. May Lord Shree Krishna, the merciful, bless

and guide my wisdom in the pursuit of knowledge and happiness in this journey

v

CONTENTS

DEDICATION ii ACKNOWLEDGEMENTS iii CONTENTS v SUMMARY xx LIST OF PUBLICATIONS xxv

CHAPTER - 1. INTRODUCTION 1

1. INTRODUCTION 2

1.1. Research background on polyimides and fluoro-polyimides

2

1.1.1. High performance polymeric materials 2

1.1.1.1. Thermosets resins 4

1.1.1.2. Manufacturing process technology for thermosetting polymers

5

1.1.1.3. Trends in R&D of high performance polymers 6

1.1.2. Polyimides 7

1.1.2.1 History of commercial development of polyimides 10

1.1.2.2. Brief history on polyimide R&D and worldwide major commercial product introduction

11

1.1.2.3. Brief summary of polyimide market size and growth projection (year 2000 to 2010)

20

1.1.2.4. Brief summary of literature survey on worldwide polyimide R&D activities

21

1.1.2.5. Types of polyimides 25

1.1.3. Synthesis of polyimides 27

vi

1.1.3.1. Monomers 28

1.1.3.2. Polyimides by polycondensation 29

1.1.3.2.1. Polyimides from dianhydrides and diamines 31

1.1.3.2.2. Chemical mechanism of polymerization reaction 32

1.1.3.2.3. Chemical imidization reaction 35

1.1.3.2.3.1. Mechanism of chemical imidization 35

1.1.4. Fluoro-polyimides 38

1.1.5. Characterization techniques of polyimides 48

1.1.5.1. Characterization of polyimide’s chemical characteristics 48

1.1.5.2. Characterization for polyimide’s physical characteristics 48

1.1.5.2.1. Glass transition 49

1.1.5.2.2. Glass transition in copolymers and miscible polymer blends

52

1.1.6. Processes and properties 53

1.1.6.1. Processing of polyimides 53

1.1.6.2. Mechanical, thermal, and thermo-oxidative stability properties

54

1.1.6.2.2. Mechanical properties 54

1.1.6.2.3. Thermal properties 55

1.1.6.2.4. Thermo-oxidative stability (TOS) of polyimides 57

1.1.6.3. Electrical and optical properties, dimensional stability and coefficient of thermal expansion (CTE)

58

1.1.6.3.1. Electrical properties 58

1.1.6.4. Optical properties 60

1.1.6.5. Dimensional stability and CTE 61

1.1.6.6. Other properties 62

vii

1.1.7. Applications of polyimides 63

1.1.7.1. Films 64

1.1.7.2. Molded plastics 64

1.1.7.3. Fibers 65

1.1.7.4. Adhesives and varnishes 66

1.1.7.5. Printed circuit board and packaging materials 66

1.1.7.6. Photo-sensitive polyimides 68

1.1.7.7. Membrane separation 69

1.2. FUTURE OF POLYIMIDES R&D 70

1.3. SCOPE OF RESEARCH ON FLUORO-POLY(ETHER IMIDE)S (6F-PEI) PROJECT

75

1.4. REFERENCES 80

CHAPTER - 2. SYNTHESIS AND PROPERTIES OF FLUORO -POLY(ETHER IMIDE)S

94

2.1. INTRODUCTION 95

2.1.1. Research background 95

2.1.2. Research objectives 96

2.2. EXPERIMENTAL 97

2.2.1. Materials 97

2.2.2. Polymerization 98

2.2.2.1. Synthesis of poly(ether imide) (PEI) 98

2.2.2.1.A. Synthesis of fluoro-poly(ether imide) polymers 100

2.2.2.1.A.1. Synthesis of [6FDA + m-SED] fluoro-poly(ether imide) polymer

100

2.2.2.1.A.1.a. Synthesis procedure 100

viii

2.2.2.1.A.1.a.1. Step-1: Condensation polymerization procedure 100

2.2.2.1.A.1.a.2. Step-2: Chemical imidization procedure 101

2.2.2.1.B. Synthesis of non-fluorinated poly(ether imide) polymers

104

2.2.2.1.B.1. Synthesis of [PMDA + p-SED] poly(ether imide) polymer

104

2.3. FABRICATION 105

2.3.1. Polymer film preparation 105

2.3.2. Poly(amic acid) film preparation for FT-IR analysis 106

2.3.3. Thin polymer plates by compression molding 107

2.4. CHARACTERIZATION 107

2.4.1. Solubility of solid polymers 107

2.4.2. Viscosity of polymers 107

2.4.3. Fourier transform-IR (FT-IR) spectroscopy 109

2.4.4. Gel permeation chromatography (GPC) [a.k.a. Size exclusion chromatography (SEC)]

110

2.4.5. Density of polymer films 112

2.4.6. Hydrolytic stability 112

2.4.7. UV-VIS spectroscopy 113

2.4.8. Differential scanning calorimetry (DSC) 113

2.4.9. Thermogravimetric analysis (TGA) 114

2.4.10. Thermo-oxidative stability (TOS) 114

2.4.11. Dynamic mechanical analysis (DMA) 115

2.4.12. Thermal mechanical analysis (TMA) 115

2.4.13. Coefficient of thermal expansion (CTE) 116

2.4.14. X-ray diffraction (XRD) 116

2.4.15. Mechanical properties 117

ix

2.4.16. Dielectric analysis (DEA) 117

2.4.17. Rheology 120

2.5. RESULTS AND DISCUSSION 122

2.5.1. Properties 122

2.5.1.1. Poly(ether imide)’s chemical structural characteristics 122

2.5.1.2. Solubility 123

2.5.1.3. Viscosity and molecular weights 124

2.5.1.4. Glass transition temperature (Tg) 125

2.5.1.5. Thermal stability and degradation 130

2.5.1.6. Thermo-oxidative stability (TOS) 135

2.5.1.7. Thermo-mechanical properties 136

2.5.1.8. Coefficient of thermal expansion (CTE) 137

2.5.1.9. Transparency and color 137

2.5.1.10. Hydrolytic stability 139

2.5.1.11. Morphology 140

2.5.1.12. Mechanical properties 141

2.5.1.13. Electrical properties 142

2.5.1.14. Polymer melt flow viscosity stability 143

2.6. CONCLUSION 144

2.7. REFERENCES 145

CHAPTER - 3. SYNTHESIS AND PROPERTIES OF DESIGNED LOW-K FLUORO- COPOLY(ETHER IMIDE)S

152



x



3.2.1. Materials 160

3.2.2. Polymerization 161

3.2.2.1. Synthesis of fluorinated poly(ether imide)s 162

3.2.2.1.1. Synthesis of fluoro-poly(ether imide) (6F-PEI) polymers

162

3.2.2.1.1.A. Synthesis of [6FDA + p-SED] fluoro-poly(ether imide) polymer

162

3.2.2.1.1.A.1. Synthesis procedure 163

3.2.2.1.1. A.2. Chemical imidization procedure 163

3.2.2.2. Synthesis of fluorinated copoly(ether imide) polymers 164

3.2.2.2.1. Synthesis of fluoro-copoly(ether imide) (6F-CoPEI) polymers

164

3.2.2.2.1.A. Series 1: Synthesis of [6FDA + (n Mole %) p-SED + (m Mole %) BPADE ] fluoro-copoly(ether imide) polymer

165

3.2.2.2.1.A.1. Synthesis of [6FDA + 75 mole% p-SED + 25 mole% BPADE ] fluoro-copoly(ether imide) polymer

165

3.2.2.2.1.A.1.1. Synthesis procedure 166

3.2.2.2.1.A.1.1.a. Step-1: Polymerization 166

3.2.2.2.1.A.1.1.b. Step-2: Chemical imidization 166

3.2.2.2.1.B. Series 2: Synthesis of [6FDA + (n Mole %) p-SED + (m Mole %) BDAF ] fluoro-copoly(ether imide) polymer

167

3.2.2.2.1.B.1. Synthesis of [6FDA + 75 mole% p-SED + 25 mole% BDAF] fluoro-copoly(ether imide) polymer

167

3.2.2.3. Synthesis of non-fluorinated polyimides (PI) 168

3.2.2.3.A. Synthesis procedure 168

3.2.2.3.A.1. Synthesis of poly(amic acid) (PAA) 168

3.2.2.3.1. Synthesis of [ODPA + m-Tolidine] poly(amic acid) (PAA) 169

xi

3.2.2.4. Synthesis of fluoro-polyimides (6F-PI) 170

3.2.2.4.1 Synthesis of [6FDA + m-PDA] fluoro-polyimide polymers

171

3.2.2.5. Synthesis of fluoro-copolyimides (6F-CoPI) 171

3.2.2.5.1. Synthesis of [6FDA + 50 mole% m-PDA + 50 mole% p-PDA] fluoro-copolyimides polymer

171


3.3.1. Polymer film preparation 173


3.4.1. Viscosity of polymer 174

3.4.2. Fourier transform-IR spectroscopy (FT-IR) 174

3.4.3. Gel permeation chromatography (GPC) 174

3.4.5. Solubility of polymer solids 174







3.4.11. Dielectric analysis (DEA) 176



3.5.2. Polymer’s chemical structural characteristics 176

3.5.3. Solubility 180

3.5.4. Viscosity and molecular weights 180

3.5.5. Color and transparency of polymer films 185

xii

3.5.6. Moisture uptake 187

3.5.7. Glass transition temperature (Tg) 187

3.5.8. Thermal decomposition temperatures and stability 190

3.5.9. Thermal stability and degradation kinetics study 191

3.5.10. Thermo-oxidative stability (TOS) study 196

3.5.11. Thermomechanical properties 198

3.5.12. Electrical properties 200

3.5.12.1. Dielectric properties of polyimides and copolyimides 200

3.5.12.1.1. Dielectric behavior of non-fluorinated polyimide (PI)

201

3.5.12.1.2. Dielectric behavior of fluorine-containing polyimide (6F-PI)

202

3.5.12.1.3. Dielectric behavior of fluoro-copolyimides (6F-CoPI) 204

3.5.12.2. Estimation of dielectric constant (ε’) of polyimides and copolyimides

206

3.5.12.2.1. Estimation of dielectric constant of polyimides (PI) 207

3.5.12.2.1.1. Calculation of ‘Molar Polarization’ of ‘Phthalimide’ groups

207

3.5.12.2.1.1.A. Estimation of dielectric constant of ULTEM-1000 [BPADA + m-PDA] polyimide polymer

209

3.5.12.2.1.2. Calculation of ‘Molar Polarization’ of ‘Pyromellitimide’ group

211

3.5.12.2.1.2.A. Estimation of dielectric constant of [PMDA + 3,3-ODA] polyimide

213

3.5.12.2.1.3. Estimation of dielectric constant of lab synthesized fluoro-polyimides (6F-PI)

215

3.5.12.2.2. Estimation of dielectric constant of copolyimides (Co-PI)

217

3.5.12.2.2.1. Dielectric constant of fluorine-containing copolyimides (6F-CoPI)

219

3.5.12.2.2.2. Dielectric constant of fluoro-poly(ether imide)s (6F-PEI) and fluoro-copoly(ether imide)s (6F-CoPEI)

219

xiii

3.5.12.2.2.2.A. Dielectric constant as a function of fluorine content in

copoly(ether imide) polymers

222

3.5.12.2.2.3. Additional ‘Molar Polarization’ values for calculation of dielectric constants by additive groups contributions

223

3.5.12.2.2.4. Importance of pre-estimation of dielectric constant value of polyimide polymers

223

3.5.13. Morphology 223

3.6. CONCLUSION 228

3.7. REFERENCES 230

CHAPTER - 4. PREPARATION AND CHARACTERIZATION OF 4,4-BIS (4-AMINOPHENOXY) DIPHENYL SULFONE BASED [FLUORO-POLY(ETHER IMIDE)/ORGANO-MODIFIED CLAY] NANOCOMPOSITES

237





4.2.1. Materials 241

4.2.2. Synthesis 241

4.2.2.1. Preparation of p-SED (Diamine) modified MMT clay 241

4.2.2.1.1. Procedure of making p-SED (Diamine) modified MMT clay

243

4.2.2.1.2. Synthesis of fluoro-poly(ether amic acid) 243

4.2.2.1.2.1. Master batch of fluoro-poly(ether amic acid) (6F-PEAA) 244

4.2.2.1.2.1.1. Synthesis procedure 244

4.2.2.1.3. Preparation of p-SED treated MMT clay suspensions in NMP

245

xiv

4.2.2.1.4. Preparation of fluoro-poly(ether amic acid)/MMT clay nanocomposites pre-formulations

245


4.3.1. [6FDA + p-SED] Fluoro-poly(ether imide), and [6FDA + p- SED]/MMT clay nanocomposite film preparation

246


4.4.1. Viscosity of polymer 248

4.4.1.1. Inherent viscosity 248

4.4.1.2. Bulk viscosity 249

4.4.2. Fourier transform-IR spectroscopy (FT-IR) 249

4.4.3. Gel permeation chromatography (GPC) 249


4.4.5. Solubility of polymer films 249






4.4.11. Thermal mechanical analysis (TMA) 251

4.4.12. Mechanical properties 251

4.4.13. Surface properties 251



4.5.1.1. [6FDA + p-SED] Fluoro-poly(ether imide)’s chemical structural characteristics

252

4.5.1.2. Viscosity and Molecular weights 253

xv

4.5.1.3. Solubility of [6FDA + p-SED] (6F-PEI) and [(6F-PEI)/ MMT clay] nanocomposite films

254

4.5.1.4. Morphology 255

4.5.1.5. Color and transparency of polymer and nanocomposite films

256

4.5.1.6. Glass transition temperature (Tg) 256

4.5.1.7. Thermal properties 258

4.5.1.7.1. Thermal stability 258

4.5.1.7.2. Kinetics study of thermal degradation 260

4.5.1.7.3. Thermo-oxidative stability (TOS) study 262

4.5.1.8. Thermomechanical properties 263

4.5.1.9. Coefficient of thermal expansion (CTE) 265

4.5.1.10. Hydrolytic stability 266

4.5.1.11. Mechanical properties 267

4.5.1.12. Surface properties 268

4.5.1.12.1. One-liquid method 270

4.5.1.12.2. Two-liquid geometric mean method 270

4.6. CONCLUSION 274

4.7 REFERENCES 276

CHAPTER - 5. GENERAL CONCLUSIONS AND RECOMMENDATIONS

283

5.1. Conclusions 284

5.2. Recommendations 288

APPENDIX – A SYNTHESIS OF POLYIMIDE POLYMERS 291

A-1. POLYMER SYNTHESIS 292

xvi

A-2. Synthesis of fluoro-poly(ether imide)s 292

A-2.1. Reaction scheme of synthesis of fluoro-poly(ether imide) (6F-PEI)

292

A-2.1.2. Synthesis of [6FDA + p-SED] fluoro-poly(ether imide) polymer

292

A-2.1.3. Synthesis of [6FDA + BPADE] fluoro-poly(ether imide) polymer

293

A-2.1.4. Synthesis of [6FDA + BDAF] fluoro-poly(ether imide) polymer

294

A-2.2. Synthesis of non-fluorinated poly(ether imide)s

294

A-2.2.1. Reaction scheme for synthesis of poly(ether imide) (PEI) 295

A-2.2.2. Synthesis of [PMDA + m-SED] poly(ether imide) polymer

295

A-2.2.3. Synthesis of [PMDA + BPADE] poly(ether imide) polymer

296

A-2.2.4. Synthesis of [PMDA + BDAF] poly(ether imide) polymer

296

A-2.2.5. Synthesis of [BPDA + p-SED] poly(ether imide) polymer

297

A-2.2.6. Synthesis of [BPDA + m-SED] poly(ether imide) polymer

298

A-2.2.7. Synthesis of [BPDA + BPADE] poly(ether imide) polymer

298

A-2.2.8. Synthesis of [BPDA + BDAF] poly(ether imide) polymer

299

A-2.2.9. Synthesis of [BTDA + p-SED] poly(ether imide) polymer

299

A-2.2.10. Synthesis [BTDA + m-SED] poly(ether imide) polymer

300

A-2.2.11. Synthesis of [BTDA + BPADE] poly(ether imide) polymer

301

A-2.2.12. Synthesis of [BTDA + BDAF] poly(ether imide) polymer

301

A-2.2.13. Synthesis of [ODPA + p-SED] poly(ether imide) polymer

302

A-2.2.14. Synthesis of [ODPA + m-SED] poly(ether imide) polymer

302

A-2.2.16. Synthesis of [ODPA + BPADE] poly(ether imide) polymer

303

A-2.2.16. Synthesis of [ODPA + BDAF] poly(ether imide) polymer

304

A-2.3. Synthesis of fluorinated copoly(ether imide) (6F-CoPEI) polymers

304

xvii

A-3.1. Reaction scheme for synthesis of fluoro-copoly(ether imide) (6F-CoPEI)

305

A-3.2.1. Series-1: Synthesis of [6FDA + (n Mole%) p-SED + (m Mole%) BPADE] fluoro-copoly(ether imide) polymer

305

A-3.2.1.1. Synthesis of) [6FDA + (50%) p-SED + (50%) BPADE] fluoro-copoly(ether imide) polymer

305

A-3.2.1.2. Synthesis of [6FDA + (25%) p-SED + (75%) BPADE] fluoro-copoly(ether imide) polymer

306

A-3.2.2. Series-2: Synthesis of [6FDA + (n Mole%) p-SED + (m Mole%) BDAF fluoro-copoly(ether imide) polymer

307

A-3.2.2.1. Synthesis of [6FDA + (50%) p-SED + (50%) BDAF] Fluoro-copoly(ether imide) polymer

307

A-3.2.2.2. Synthesis of [6FDA + (25%) p-SED + (75%) BDAF] fluoro-copoly(ether imide) Polymer r

308

A-3.3. Synthesis of polyimides and copolyimides for electrical properties studies

308

A-3.3.1. Synthesis of poly(amic acid) (PAA) 309

A-3.3.1.A. Synthesis reaction scheme 309

A-3.3.1.2. Synthesis of [PMDA +3,3-ODA] poly(amic acid) (PAA)

310

A-3.3.1.2. A. Synthesis procedure 310

A-3.3.2. Synthesis of fluoro-polyimide (6F-PI) 310

A-3.3.2.1. Synthesis reaction scheme for fluoro-polyimide (6F-PI)

311

A-3.3.2.2. Synthesis of [6FDA + p-PDA] fluoro-polyimide polymer

311

A-3.3.2.3. Synthesis of 6FDA + 1,4-Diamino Durene] fluoro-polyimide polymer

312

A-3.3.2.4. Synthesis of [6FDA + 4,4-ODA] fluoro-polyimide polymer

313

A-3.3.2.5. Synthesis of [6FDA + 4,4-6F-Diamine] fluoro-polyimide polymer

313

A-3.3.3. Synthesis of fluoro-copolyimide (6F-CoPI) 314

A-3.3.3.1. Synthesis reaction scheme for fluoro-copolyimides (6F-CoPI)

314

xviii

A-3.3.3.2. Synthesis of [6FDA + (50%) 1,4-Diamino Durene + (50%)

p-PDA] fluoro-copolyimide polymer

315

A-3.3.3.3. Synthesis of [6FDA + (50%) 1,4-Diamino Durene + (50%) m-PDA] fluoro-copolyimide polymer

315

APPENDIX - B ESTIMATION OF DIELECTRIC CONSTANT (ε’) OF POLYIMIDE POLYMERS

317

B-1. Non-fluorinated polyimide polymers 318

B.1.1. Estimation of dielectric constant of [ODPA + m-Tolidine] polyimide

318

B.1.2. Estimation of dielectric constant of [PMDA + 3,3-ODA] polyimide

319

B.1.3. Estimation of dielectric constant of [BPDA + m-PDA] polyimide

320

B.1.4. Estimation of dielectric constant of UPILEXR [BDPA + 4,4-ODA] polyimide

321

B.2. Fluoro-polyimides 322

B.2.1. Estimation of dielectric constant of [6FDA + m- PDA] fluoro-polyimide

322

B.2.2. Estimation of dielectric constant of [6FDA + p- PDA] fluoro-polyimide

323

B.2.3. Estimation of dielectric constant of [6FDA + 1,4-Diamino Durene] fluoro-polyimide

324

B.2.4. Estimation of dielectric constant of [6FDA + 4,4-6F-Diamine] fluoro-polyimide

325

B.2.5. Estimation of dielectric constant of [6FDA + 4,4-ODA] fluoro-polyimide

326

B-3. Fluoro-copolyimide 327

B-3.1. Estimation of dielectric constant of [6FDA + (50%) m- PDA + (50%) p-PDA] fluoro-copolyimide

327

xix

B-3.2. Estimation of dielectric constant of [6FDA + (50%) m- PDA + (50%) 1,4-Diamino Durene] fluoro-copolyimide

328

B-3.3. Estimation of dielectric constant of [6FDA + (50%) p- PDA + (50%) 1,4-Diamino Durene] fluoro-copolyimide

329

B-4. Fluoro-poly(ether imide)s 330

B-4.1. Estimation of dielectric constant of [6FDA + p-SED] fluoro-poly(ether imide)

330

B-4.2. Estimation of dielectric constant of [6FDA + BPADE] fluoro-poly(ether imide)

331

B-4.3. Estimation of dielectric constant of [6FDA + BDAF] fluoro-poly(ether imide)

332

B-5. Fluoro-copoly(ether imide)s 333

B-5.1. Estimation of dielectric constant of [6FDA + (75%) p-SED + (25%) BPADE] fluoro-copoly(ether imide)

333


334


335

B-5.4. Estimation of dielectric constant of [6FDA + (75%) p-SED + (25%) BDAF] fluoro-copoly(ether imide)

336


337


338

xx

SUMMARY

Polyimides are one of the important classes of versatile engineering polymers as they

exhibit reasonably good mechanical properties, chemical resistance, low dielectric

constant and thermal stability, when compared to other polymeric materials. They are

therefore, prominent polymers amongst high performance, high temperature stable

organic materials. The higher glass transition temperatures (Tg) of polyimides are due to

structural rigidity of dianhydrides. The Tgs of these polyimides are in the range of 250 to

410°C. However, high softening points and intractability of polyimides have limited their

direct usage in electronic applications. Hence the search for new polyimides with

improved processability and higher continuous use (200°C) temperatures than the

commercially available polyimides, and poly(ether imide) has received a significant

attention from both academia and industries. The approach involving the modification of

the backbone structure of polyimides, such as an incorporation of a flexible ether linkage

and meta oriented phenylene rings into polymer backbone has provided an increase in

chain flexibility and solubility, but has also lowered the effective upper use temperature.

More importantly, in microelectronic device circuitry, the propagation velocity of

signal is inversely proportional to the square of the dielectric constant (ε’) of the

propagation medium. Therefore, a low dielectric constant is necessary for a faster signal

propagation in microelectronic devices without cross-talk, especially for newer

multilevel high-density and high-speed electronic circuits as the geometry is further

miniaturized. A desirable value should be below 3.1 at 1 kHz. The dielectric constant of

commercially available polyimides, such as Kapton-H, [PMDA + p-ODA], Upilex-S

[BPDA + p-PDA], poly(ether imide) ULTEM-1000, [BPADA + m-PDA] and fully

fluorinated poly(ether imide) EYMYD [6FDA+BDAF], is in the range of 2.99 to 3.5.

xxi

Even though, EYMYD met the requirements of low ε’, high thermal stability and

continuous use temperature in the range of 170-200°C, but it was commercially available

for a short time only in its amic acid solution form (an unstable material with short shelf

life), and it was prohibitively expensive. Both Kapton-H and Upilex-S (Tg >400°C)

having higher ε’ (~3.5) and higher moisture absorption in the range of 1.5-2.8%, are

available only in non-thermoplastic film forms. Whereas, ULTEM1000, a melt

processable resin (Tg 218°C) due to its higher moisture absorption (~1.5%), lower

continuous use temperature (~170°C) and higher ε’ (3.15) is unattractive for newer

200°C continuous use temperature microelectronics fabrication applications.

During the last 15 years, clay-polymer nanocomposites and hybrids have become an

emerging field of research and development because of their unique microstructures, and

enhanced properties. These organic polymer/inorganic hybrid or nanocomposite

materials (Ceramers) are expected to exhibit unique characteristic and synergistic

properties of both ceramics and organic polymers. Presently, perfect ‘Ceramer’ materials

with all the desired properties, (Viz. mechanical property retention at high temperature,

low thermal expansion, toughness, ductility, and processebility, etc.) based on

‘polyimides’ chemistry have not been developed or marketed yet. When developed, these

new materials would provide unique properties for potential applications for electronics,

electrical, aerospace, life science, separation membranes, MEMS, etc. industries.

The objective of the present research work was to synthesize, fabricate, characterize,

and to study the properties and thermal degradation kinetics of ‘low-K’ poly(ether

imide)s and copoly(ether imide)s, and poly(ether imide)/organo-soluble MMT clay

nanocomposites film.

The effort for the thesis research work as reported in Chapter 2 was focused on the

synthesis, characterization, and study of a series of high-performance partially

xxii

fluorinated poly(ether imide) (6F-PEI) from commercially available monomers. The

approach involved the polymerization of 2,2-bis(3,4-dicarboxyphenyl)

hexafluoropropane dianhydride (6FDA) with a variety of diether-containing non-

fluorinated diamines, viz. 4,4-bis(3-aminophenoxy)diphenyl sulfone (m-SED), 4,4-bis(4-

aminophenoxy)diphenyl sulfone (p-SED), 4,4-bis(4-aminophenoxy)diphenyl propane

(BPADE) by a simplified one-pot two-step solution polymerization process. These (6F-

PEI) polymers were characterized for their chemical properties, solubility, morphology

nature, hydrolytic stability, thermal behavior, thermo-oxidative stability (TOS),

thermomechanical, mechanical, electrical, transparency and melt rheology properties in

order to understand their structure-property relationships.

Chapter 3 describes the synthesis, characterization and study of designed low-K

fluoro-copoly(ether imide)s (6F-coPEI). The synthesis methodology of these polymers

was similar to that described in Chapter 2. However, before the actual synthesis of (6F-

coPEI)s, several polymer compositions were first designed and their dielectric constant

(ε’) values were pre-estimated by means of mathematical equations defined by the

Lorentz-Lorenz’s theory, the Vogel’s theory, and Vora-Wang equations. Then, a series

of (6F-PEI) and selected few (6F-coPEI)s having low dielectric constant values (by

estimation) were successfully synthesized and their films were similarly characterized as

discussed in Chapter 2, to study their thermal degradation kinetics, electrical, TOS and

hydrolytic stability, etc. properties, and to understand the effect of chemical structure of

co-monomer (diamine) on their thermal stability.

A series of (6F-PEI)/organo-soluble MMT clay nanocomposite formulations were also

prepared from the [6FDA+p-SED] poly(ether amic acid) having blended with varying

concentration of organo-soluble clay, and their films were characterized to understand

xxiii

the effect of varying concentration of organo-soluble clay on the nano-composite’s

thermal, mechanical and surface properties as reported in Chapter 4.

The FTIR study confirmed that poly(ether amic acid)s (6F-PEA) were successfully

converted to (6F-PEI) by chemical imidization method. The inherent viscosities of these

(6F-PEA), (6F-coPEA), (6F-PEI), and (6F-coPEI) were determined by viscometry. The

XRD measurements confirmed that (6F-PEI), and (6F-CoPEI) were amorphous

polymers. Glass transition temperatures (Tg) of copolymer films were predicted from the

Fox equation, and compared with the results of differential scanning calorimetry (DSC)

measurements. Thermogravimetric analysis (TGA) measurement data and the Coats &

Redfern equation were used in the thermal degradation kinetics calculation for the

determination of activation energy (Ea) of polymer degradation. The thermal stability

results were comparable to the TOS data obtained by isothermal heating of films in air at

315°C for 300 hr. The films (6F-PEI), (6F-CoPEI) and nanocomposites having

trifluoromethyl groups not only showed extraordinary long-term TOS, but also exhibited

excellent reduced water absorption relative to non-fluorinated polyimides. Estimated ε’

values for (6F-CoPEI)s films were verified against actual measured values obtained by

dielectric analysis (DEA) at 1 kHz. The estimated values were in good agreement with

experimental as well as literature values.

The films of the [6FDA+p-SED]/MMT clay nanocomposites showed excellent solvent

resistance, also increased Tg and a sharp lowering of coefficient of thermal expansion

(CTE) with increasing clay content. Modulus of elasticity determined by an Instron

mechanical analyzer, on an average, increased for the nanocomposite films relative to

neat fluoro poly(ether imide) [6FDA+p-SED], and films of ‘control’ non-fluorinated

polyimides. The surface energy measurements by the One-Liquid and Two-Liquid

Geometric Mean methods showed comparable trend of decreasing contact angle which is

xxiv

an indication of improved wettability and/or adhesion, a desirable property for

microelectronic applications.

xxv

LIST OF PUBLICATIONS

Journal Publications: (* Corresponding author)

1. Rohitkumar H. Vora*, Suat Hong Goh, Tai-Shung Chung, “Synthesis and

Properties of Fluoro-Poly(ether imide)s”, Polymer Engineering & Science, 40(6)

(2000), 1319-1329.

2. Rohitkumar H. Vora*, P. Santhana Gopala Krishnan, Suat Hong Goh, Tai-

Shung Chung, “Synthesis and Properties of Designed Low K Fluoro-

Copoly(ether-imide)s -Part 1.”, Advanced Functional Materials, 11(5) (2001),

361-373.

3. P. Santhana Gopala Krishnan, Rohit H. Vora*, S. Veeramani, Suat Hong

Goh, Tai-Shung Chung, “Kinetics of Thermal Degradation of 6FDA Based

Copolyimides-I”, Polymer Degradation and Stability, 75(2) (2002), 273-285.

4. Rohitkumar H. Vora*, Pramoda K. Pallathadka, Suat Hong Goh, Tai-Shun

Chung, Yong Xiong Lim, Toong Kiang Bang. “Preparation and

Characterization of 4,4’-Bis(4-aminophenoxy) Diphenyl Sulfone Based Fluoro-

Poly(ether imide)/Organo-modified Clay Nanocomposites”, Macromolecular

Materials and Engineering, 288(4) (2002) 337-356

Book Chapters: (* Corresponding author)

1. Polyimide Syntheses, Characterization, Blends and Applications, T. S. Chung, J.

Pan, S. L. Liu, S. Mullick, R. H. Vora. in Advanced Functional Molecules and

Polymers, H. S. Nalwa, (Ed.) Vol. 4, p. 157, Gordon & Breach Publishers, New

Yoyk, 2001.

2. Measurement and Theoretical Estimation of Dielectric Properties of Polyimides,

Rohit Vora*, Huimin Wang, Tai-Shung Chung. in Polyimides and Other High

Temperature Polymers, K. L. Mittal, (Ed.) Vol. 1, p. 33, VSP Utrecht, The

Netherlands, 2001.

3. Polyamic Acids and its Ionic Salt Solution: Synthesis, Characterization and its

Storage Stability Study, Rohit H. Vora*, P. Santhana Gopala Krishnan, S.

xxvi

Veeramani, Suat Hong Goh, in Polyimides and Other High Temperature

Polymers, K. L. Mittal, (Ed.), Vol. 2, p. 3, VSP Utrecht, The Netherlands, 2003.

Conference Presentations: (# Invited paper,* Corresponding author, $ Session

Chair)

1. Rohit Vora #, *, $, Tai -Shung Chung, “Development of Fluoro-Poly(ether

imide)s for Electronics Applications: Synthesis and Characterization”, in

proceedings of the 5th Symposium on Polyimides and High Performance

Functional Polymers (STEPI-5), in Polyimides and High Performance Polymers,

M. J. M. Abadie, B. Sillion (Eds.), STEPI-5, ISIM, Montpellier, FRANCE, 1999,

p. 52.

2. Rohit H. Vora #, *, $, P. Santhana Gopala Krishnan, Suat Hong Goh, T-S

Chung, “Low K Fluoro-Copoly(ether imide)s derived form Di-ether containing

Diamines and 6FDA: Synthesis and Properties,” in proceedings of the 7th

International Conference on Polymers for Electronics Packaging–RETECH 2000,

in Advances in Low-k Dielectric and Thermally Stable Polymers for

Microelectronics, H. Sachdev, M. M. Khojasteh, D. McHerron (Eds.), Society of

Plastics Engineers, Brookfield, USA, 2002, p-71.

3. Rohit H. Vora #, *, $, P. Santhana Gopala Krishnan, S. Veeramani, Suat

Hong Goh, Tai-Shung Chung, “Thermal Degradation Studies of 6FDA Based

Copolyimides,” in proceedings of the 7th International Conference on Polymers

for Electronics Packaging–RETECH 2000, in Advances in Low-k Dielectric and

Thermally Stable Polymers for Microelectronics, H. Sachdev, M. M. Khojasteh,

D. McHerron (Eds.), Society of Plastics Engineers, Brookfield, USA, 2002, p.

355.

4. Rohit H. Vora #, *, $, Pramoda K. Pallathadka, Suat Hong Goh,

“Development of Fluoro Poly(ether imide)s/MMT Clay Nanocomposites:

Synthesis and Characterization”, in proceedings of the 6th Symposium on

Polyimides and High Performance Functional Polymers (STEPI-6), in Polyimides

and High Performance Functional Polymers, M. J. M. Abadie, B. Sillion (Eds.),

STEPI-6, ISIM, Montpellier, FRANCE, 2003, p 191

1

CHAPTER - 1

INTRODUCTION

2

1. INTRODUCTION 1.1. RESEARCH BACKGROUND OF POLYIMIDES AND FLUORO-

POLYIMIDES During the past 60 years, the world has witnessed a remarkable development in

structural material technologies; new nonmetallic materials such as ceramics and

polymer matrix composites are replacing metals in a wide variety of industrial, aerospace

and consumer applications, ranging from highly specialized spacecraft structural

components, cryogenic rocket engines, cutting tools to tennis rackets. [1-7]

1.1.1. High performance polymeric materials

In aerospace applications, highly specialized spacecraft structural components,

cryogenic rocket engines parts, military aircraft components, etc. are made up of light

weight, mechanically stronger and high temperature stable composites. These composites

are made from special graphite, carbon, glass, or ceramic fibers matrix prepregs

impregnated with the advanced high performance thermosetting and/or thermoplastics

polymeric materials.

Such advanced high performance polymeric materials, resin alloys and hybrid systems

possess long-term ‘service temperature’ capabilities in the range from room temperature

to >150 °C. The service temperature is based upon the ‘Thermal Index’ rating assigned

by the Underwriters’ Laboratories (UL) of USA. The UL relative Thermal Index is an

indication of the thermal stability of a polymer. Underwriters’ Laboratories addresses

this phenomenon with the UL Temperature Index. The temperature indices are used by

UL as a guideline when they compare hot spots on devices and appliances made from

these materials. Higher ‘Thermal Index’ rating for a particular polymeric material means

that it would continuously provide a long term thermal stability in terms of good

mechanical strength, good environmental stability, dimensional stability, solvent

3

resistance, and electrical properties at the elevated temperature for which it is rated. UL

defines the end of service life as the aging time required to produce a 50% drop in the

property compared with the initial value [8].

A typical list of high service temperature polymers (thermoset and thermoplastics)

including linear, and heterocyclic types that are commercially used in current electronics,

aerospace, automotive, electrical industries is given below. [1-5, 9-10]

Epoxy

Polyarylate (PA)

Liquid crystal polymers (LCP)

Polycarbonate (PC)

Poly(p-phenylene sulphide) (PPS)

Polyethersulfone (PS)

Polyketones

Poly(ether ether ketone) (PEK or PEEK)

Polyimides (PI)

Fluoro-polyimide (6F-PI)

Bismaleimide (BMI)

PMR-15

Poly(amide-imide) (PAI)

Polyamide

Poly(ether imide) (PEI)

Polyphenylquinoxaline (PPQ)

Polybenzoxazole (PBO)

Polybenzimidazole (PBI)

Etc.

As shown in the Table 1 below, some of these polymers have mechanical properties

typically required for high performance composites for aerospace applications.

Not every industry sector uses high performance polymers for product development

for their specific industry related applications. There are various factors which affect the

selection of a particular polymer for a particular application or product development.

4

These factors typically include, material selection based on final product usage, product

life time, polymer’s properties, processability, and of course, the cost (a main factor for

most industries) of making that product using that particular polymer.

Table-1: Neat resin mechanical and fracture toughness properties of high performance Thermoplastics [10-11]

Tensile Properties @ 25 °C POLYMER

Yield Strength (Kpsi) (MPa)

Modulus (Kpsi) (GPa)

Strain to Break (%)

Fract. Energy (GI C)

Lb/in2 (kJ/m2)

PEEK 14.5 (100) 450 (3.1) > 40 > 23 ( > 4) PXM 8505 12.7 (88) 360 (2.5) 13 -- -- PPS 12.0 (83) 630 (4.3) 5 0.6-1.4 (0.1-0.2) PAS-2 14.5 (100) 470 (3.2) 7.3 -- -- TORLON C 20.0 (138) 550 (3.8) 15 19.4 (3.4) TORLON 696 13.0 (90) 400 (2.8) 30 20.0 (3.5) ULTEM100 15.2 (105) 430 (3.0) 60 19.0 (3.3) NR 150B2 16.0 (110) 605 (4.2) 6 13.7 (2.4) Avimid K-III 14.8 (102) 546 (3.8) 14 11.0 (1.9) LARC-TPI 17.3 (137) 540 (3.7) 4.8 10.0 (1.8) PISO2 09.1 (63) 719 (5.0) 1.3 8.0 (1.4) P-1700 10.2 (70) 360 (2.5) > 50 14.0 (2.5) SIXEF-44* 13.8 (--) 405 (--) 7.8 -- -- Epoxy (3501-6) 12.0 (70) 620 (4.3) 1.2 19.4 (3.4) 19.4 (3.4) BMI(HG89107) -- -- 450 ( 3.1) 7 19.4 (3.4)

* [10] The illustrative chart, given below in Table 2, shows the relative importance of factors

that a product development engineer would take into consideration according to his/her

final industry products applications and end-uses [3-7, 9].

1.1.1.1. Thermosets resins

For aerospace composites applications, thermosetting resins have shown some

advantages over the thermoplastic counterpart, such as low initial melt viscosity, which

provide uniform wetting, tack, and ease of handling. In addition, their good solvent

resistance, good interfacial adhesion, good mechanical performance and durability and

good damage tolerance also have ensured their use in the aerospace industries for over 50

years.

However, it was also found that these resins had some disadvantages. For example,

5

Table -2: Relative importance of factors affecting high performance resin selection by end user

the application of epoxies required complex formulations, and the resins provided poor

prepregs stability and required a long processing cycle which was economically costly.

In the case of BMI and PMR-15 type resin chemistry, the composites showed poor

toughness and thermal cracking in endurance test, indicating questionable durability.

However, extensive efforts were made in the development of processes for fabrication of

aerospace structural components by the contractors of NASA and U.S. defense industries

under DARPA funded projects. Some of the most effective processes came out of this

development are now also used commercially as discussed below.

1.1.1.2. Manufacturing process technology for thermosetting polymers

There are several processes used in the aerospace and composites industries to

manufacture large dimensioned and complex- shaped glass, ceramics, graphite,

carbon, aramide, even polyimide-fiber reinforced composites. Mostly thermosetting

resins such as BMI, PMR, epoxy, or their special blends, have been used as matrix

resins. Now due to the need for very complex geometric requirements, several high

temperature thermoplastics, such as polyaramides, polyimides, polyamideimides,

polyetherimides, etc. or their specially formulated blends are also widely used, allowing

Applications

HIGH MEDIUM LOW

Factor

Electrical

Environmental

Mechanical/Durability

Processability

Thermal Stability

Price

Consumer/Industrial

Electronics/Electrical

Aerospace AutomotiveApplications

HIGH MEDIUM LOW

Factor

Electrical

Environmental

Mechanical/Durability

Processability

Thermal Stability

Price

Consumer/Industrial


Aerospace AutomotiveConsumer/Industrial


Aerospace Automotive

6

prepreggers to closely match the dimensions of shaped components, and also to repair

the final composites products. Typical processing methods are briefly given below [3-5]:

o Wet lay-up and autoclave molding

It is generally used for larger and complex aircraft composites parts. The process

employs prepregs, such as tapes, mats or woven cloth forms and cured using vacuum

bag under controlled heating and pressure in an autoclave.

o Filament winding

It is generally used for the fabrication of cylindrical parts: rocket fuel tanks,

helicopter blades, etc. It involves the mechanical winding of continuous fiber strands

either pre- or post-resin impregnation stage.

o Compression molding

It involves the manufacturing of parts from Sheet Molding Compounds (SMC) under

very high pressure and high temperature in controlled condition in an inert

atmosphere or in vacuum.

o Pultrusion

Precision parts of constant cross section, such as rectangular beams; tubes, angles,

etc. are made by this process. Continuously pulling resin-coated fibers through a

heated die results in partially or fully cured parts. The former ones are cured in the

final conversion stage in an autoclave.

1.1.1.3. Trends in R&D related to high performance polymers

Since the early 1990s, there has been a definite worldwide trend towards the R&D

spending for the further development high performance polymers, and extending such

polymers’ usage to the electronics sector, which put forth large efforts in the application

product development. This has lead to the high usage of performance polymers in the

electronic industries increasing faster than in the aerospace and military hardware

7

industry sector. However, due to specific favorable processing conditions, thermoplastics

polymers took lead in R&D efforts over thermosetting polymers.

Market survey showed that beside thermosetting epoxies, condensation polymers

having thermoplastic nature such as thermoplastic polyimide (TPI), liquid crystal

polymers (LCP), polyetheretherketone (PEEK), polyetherimides (PEI), fluoro-polyimide,

had been used in the product development of very large scale integrated (VLSI) circuits,

micro ball greed array (BGA) packages, flex circuit substrates, etc. Of course, the

development of high-temperature service applications continues to be funded by major

US and foreign Government’s defense industries.

The illustrative chart given in Figure 1 below shows the major trend in high

performance polymer R&D efforts. [6-7, 9, 12]

Figure-1: Trends in high performance polymers development [6-7, 9, 12].

Today polyimide and related chemistry based polymeric materials are used in

electronics and aerospace industries. The market has been driven by performance, and

more recently by the life cycle of products, and ultimate cost considerations. [6-7, 9, 12-

13]

1.1.2. Polyimides

Ceramic, graphite, carbon, even glass fiber reinforced composites using polyimides as

AdditionPolyimides

ToughenedBM ICROSS

LINKED AMORPHOUS

ToughenedEPOXY

CondensationPolyimides

TPI

PAI

LCP

PEIPEEK(HTX)

PEEKPPSEPOXY

Silicones

LOW TEMPERATURE

HIGH TEMPERATURE

BM I

AdditionPolyimides

ToughenedBM ICROSS

LINKED AMORPHOUS

ToughenedEPOXY

CondensationPolyimides

TPI

PAI

LCP

PEIPEEK(HTX)

PEEKPPSEPOXY

Silicones

LOW TEMPERATURE

HIGH TEMPERATURE

BM I

8

a matrix resin are increasingly being used in military engineering and aerospace

applications because of their high strength-to-weight ratios and corrosion resistance. A

variety of these polymers including polyimides and copolyimides have been synthesized

by NASA, DuPont, M&T Chemicals, Ciba Geigy, National Starch, Hoechst Celanese,

and others as high performance materials, for example, as matrices for fiber reinforced

composites, foam and fibers, electronics substrate films, packaging encapsulants,

adhesives, and protective coatings. [1-2, 9-10, 14-39].

Ongoing development of improved synthesis methods has yielded a new generation of

thermosets and thermoplastic polyimides that offer broader processebility and enhanced

physical properties. Some new high temperature polymers eliminated the tendency to

brittleness and other limitations that were present in earlier products. While established

market sectors continue to account for most of the volume, the newer polymers are

making inroads in such fast-growing and exciting areas as microelectronics and

aerospace [13].

One of the key advantages of polyimides in these markets is that they can be used in a

range of -450°F (-230°C) to more than 800°F (approx. 426°C), well beyond the

capability of most organic plastics [2, 13, 15].

As mentioned earlier, polyimides constitute a very important class of advanced

materials because of the combination of many unique chemical (good hydrolytic

stability, chemical resistance, adhesion property), thermal (high stability to thermal

oxidation and irradiation), mechanical (good planarization and processability, low

thermal expansion, high mechanical strength), and electrical properties (low dielectric

constants, high breakdown voltage, low losses over a wide range of frequency) [1, 3, 16].

Polyimides can be used for applications where bismaleimides are no longer useful

thermally.

9

Through the last 50 years of research and development, numerous polyimides and

monomers for preparing polyimides have been identified and synthesized and introduced

in the market. Over 60 polyimide products, such as, Kapton [40], and Pyralin 3002

[41], Vespel [42], NR-150 [43], PMR-15, [44], LARC-TPI [10], ULTEM [45-47],

Polyimide-2080 [48-49], M&T-2065 [50], SOLIMIDE-Foam [21], XU-218 [24],

SIXEF-PI [25-38], THERMID-IP and THERMID-AF [23, 51], to name a few, have

been successfully commercialized and today play a very important role in devices for

aerospace, defense, and the electronics industry. However, polyimides also have some

inherent problems that limit their further development. These include high monomer

cost, toxicity and complex processing techniques. The synthesis of appropriate aromatic

dianhydrides and diamines with suitable functional structures is not trivial, and their

costs are prohibitive, resulting in the higher costs of polyimides, and a greater hurdle to

commercialize novel polymers. Additionally, some of the aromatic diamines and

aromatic dianhydrides are suspect carcinogens, and their restricted sale contributes to the

increased cost. This further disrupted research and development in polyimides.

Processing of polyimides was another challenge for most polymer engineers. Fully

imidized polyimides are often insoluble and infusible, rendering them difficult to be

processed.

Although polyimides have service temperature up to 700°F (371°C), they suffer from

their poor processability. But for certain electrical and electronic applications, due to

their unique properties and performance, polyimides still continue to gain applications,

and are widely used along with other polymeric materials in aerospace,

electrical/electronics insulation and defense industries today [12-16, 52-53].

The electronics and aircraft/aerospace industries are the largest current markets for

such advanced polymeric materials. The military market includes fighter, attack and

10

large transport aircraft [2-7, 9-10, 13, 20, 52]. However, by the year 2010, large markets

for ceramic and nanocomposite materials will be found mostly in microelectronics,

military, aerospace, automotive, medical, and building and construction applications [2-

7, 9, 20].

Illustrative Figure 2 shows the processing and performance requirements of polyimide

resin alloys (blends), hybrids & nanocomposites to compete against other polymers for

cost effective industrial applications.

Figure-2: High performance polymeric materials for industrial applications

1.1.2.1. History of commercial development of polyimides

Historically, polyimide was first reported in 1908 [1-2], when it was thrown away as a

useless oligomer. In 1955, DuPont successfully developed high molecular weight

aromatic polyimide [1-2]. The first patent for polyimide was applied by DuPont in 1959

[3]. The company also developed the first commercial polyimide, Kapton, in 1960 and

marketed in 1962 [4-5]. Since then, polyimides have seen more rapid development due to

the large demands of high performance polymers for aerospace projects’ requirements.

PROCESSIBILITY

PER

FOR

MA

NC

E

LOW

LOW

HIGH

HIG

H

PI

PBO

PBI

BMI

PS

PAPEK or PEEK

PEI

PAI

6F- PEIPolymeric AlloyHybridsNanocomposites

PROCESSIBILITY

PER

FOR

MA

NC

E

LOW

LOW

HIGH

HIG

H

PI

PBO

PBI

BMI

PS

PAPEK or PEEK

PEI

PAI

6F- PEIPolymeric AlloyHybridsNanocomposites

11

In this history of polyimides section, only the history of their commercial

developments including some of the very well known and important polyimide

products introductions are highlighted. Since there were over 60 polyimide chemistry

based products in the high performance polymer market segment by the year 1990, it is,

therefore, beyond the scope of this brief introduction to include each one of them.

Besides, there were several thousands of technical papers published by hundreds of

academic institutions around the globe since 1955 in the polyimide area. In most cases

these research works just remained as an academic interest only. However, they did

enhance the overall scientific knowledge on polyimides and their properties and potential

applications. From these papers, a few selected papers were reviewed in appropriate

chapters of the thesis.

1.1.2.2. Brief history on polyimide R&D and worldwide major commercial product introduction Early 1959 to 1970

DuPont introduced the first polyimide product, Kapton-H based on pyromellitic

dianhydride (PMDA) and oxy-dianiline (ODA) chemistry. By mid 1960’s DuPont had

three major polyimide products: Kapton (film), Vespal (molding), and Pyre-ML

(wire-enamel,) and developed over a period of ten year time a niche and sizable market

for the high performance polymer materials [40-44, 51-68].

1970-1975

The polyimide business grew with a rapid pace in the USA in excess of US$ 200

millions in value and 12 millions pounds (approx 5.45 million kg) in volume.

NASA Lewis led to the development of PMR technology, which is a class of

polyimides known as PMR (for in situ Polymerization of Monomer Reactants). PMR-15

is based on dimethyl esters of BTDA, and norbornene anhydride and methylene dianiline

[69-70].

12

The National Aeronautics and Space Administration (NASA)’s Langley Research

Center was actively involved in polyimide R&D and developed various poly(amic acid)s

thermoplastic formulations based on BTDA, and benzophenone group containing

diamines. These products were referred to as LARC-TPI polymers. This technology was

then made available for licensing to commercial enterprises worldwide.

Contractors of US governments’ defense related projects were major customers for

their uses in aerospace (Figure 3) and defense related applications [1-5, 23].

DuPont introduced a series of NR-150 formulation products as high temperature

adhesives for high performance composites. They were thermoplastic products used as

binders, adhesives and coatings for structural composites. They were designed for a

broad range of aerospace applications, such as radome, jet engines, brake lining ablative

heat shields, etc. [43].

Monsanto developed and introduced SKYBOND brand of thermosetting polyimide

for aerospace composite prepreg fabrication applications [4, 9].

Rhodia, Inc. of New York, based on proprietary monomers, introduced thermosetting

polyimide under the trade name of Nolimide-A 380 for extreme high temperature

(>800°F, i.e., >426°C) adhesives intended for applications in the structural composites

and construction of advanced supersonic transport and tactical fighter planes [71].

1975 - 1980

New players came in with other types of polyimides for aerospace and electrical

applications. Worldwide competition in R&D efforts expanded to a record level in the

USA. Major funding was provided by the US government for the R&D activities in

novel polyimides for defense related hardware products and application development.

NASA-Lewis, NASA-Langley and Defense Advance Research Program of Agency of

US Govt. (DARPA) were few of the leading collaborators [2-7, 9-10, 12-13, 23, 52].

13

1980 - 1985

The market expanded at an average rate of 10 to 13% per year. Most of it was in

electrical, aerospace, military aircraft and later in electronic applications. R & D efforts

and funding continued at a faster pace with an aim to develop new applications for

microelectronic industries. More new players came in with a wide variety of polyimides

and photo-polyimide products and formulations. DARPA funding increased further for

the development of polyimides for advanced highly sophisticated military applications

[3-5, 9, 12-13, 15, 20, 52, 72].

Figure-3: Application of high temperature, high performance polymers in aerospace application [23]. In 1980, Ciba-Geigy Corp. introduced XU-218 polyimides having epoxy components

as encapsulants for pin-grid packages (PGP) containing electronic circuitry on silicon

chip. Subsequently this company introduced BMI chemistry based adhesive Matrimid

series of products and Probimide a photosensitive polyimide formulation for

photolithography in microelectronics application [3-5, 9, 13, 20, 73-75].

In 1981, Plastics Product Division of General Electric Corp. (GE) introduced

ULTEM 1000 , a melt processable thermoplastic polyetherimide resin (Tg. 220°C)

14

made from bisphenol-A based di-ether containing dianhydride (BPADA) and meta-

phenylene diamine (m-PDA) [3-5, 9-10,13, 46-47, 76-77].

In 1980, Amoco successfully introduced Torlon brand poly(amide-imide) based on

trimellitic anhydride (TMA) and methylene dianiline (MDA) for commercial engineering

applications [3-5, 20].

In 1981, M&T Chemicals, Inc. invented and introduced siloxane–imide moiety

containing M&T-PSI series of poly(amic acid) and polyimide products based on a

proprietary siloxane diamine, novel diether dianhydride and diamines. These products

were: M&T 2065, M&T 3500, M&T 4605-40, M&T 5000, M&T 1112, M&T CNF-

1114. and M&T Rely-imide. The potential applications were: protective coatings for

high voltage high tension power-lines and electro-magnate wires for power generation

station, and coatings for space satellite’s solar cells and solar sail protection from space

debris, etc., high performance adhesives for Copper-Kapton film laminates, silver filled

die-attached adhesives for flexible circuits and junction coatings, low temperature curing

encapsulants, as well as matrix resins for light weight, high temperature stable, high

performance composites for aerospace, etc. [18-19, 50, 78-86]. This business was later

acquired by National Starch and Chemicals Co of NJ, USA in 1988.

In 1982, Hitachi Chemicals Co. Ltd., Tokyo, Japan introduced PIQ, PIX and HL series

of heat resistant fine polymers for dielectric insulation and passivation of semiconductor

devices [87].

In 1982, the Donald S. Gilmore Laboratory of Upjohn Company introduced polyimide

and fiber under brand name of Upjohn Polyimide 2080. It was an extension of its

aromatic isocyanates business. This business was subsequently acquired by Dow in

1985. The products then were marketed as Dow 2080 series of polyimides. They were

based on BTDA, MDI and other di-isocyanates, for thermoplastic application in printed

15

circuit boards, composites for structural components of aircraft and aerospace [3-4, 9-10,

13, 48-49].

In 1985 E. M Industries’ Merck Electronics Products Division introduced Slectilux-

HTR3 polyimide based photoresists formulations in Germany [88].

In 1985, IMI-Tech, Inc. a subsidiary of International Harvester, Co., introduced

SOLIMIDE (Polyimide Foam) based on dimethyl ester of BTDA and MDA and

siloxane diamine (M&T) for “Non-flammable” aerospace-craft, and military aircraft’s

acoustic and thermal insulation applications.[3-5, 21, 89-94].

1985-1990

For the first time in the history of polyimide, in 1986, National Starch and Chemical

Corp. introduced the first series of aminophenyl acetylene-terminated isoimide oligomer

based on BTDA and aminophenoxy benzene (APB) chemistry, under the trade name

THERMID. Later in 1987, it introduced aminophenyl acetylene terminated fluorinated

isoimide oligomers based on 6FDA and APB [9, 13, 23, 51].

In 1986, Boots-Technochemie, a subsidiary of Boots Company PLC, UK introduced

another BMI-chemistry based series of thermosetting resin products with the brand name

of COMPIMIDE for void-free fiber reinforced laminates and molding applications in

aerospace industries.[95].

Rohm and Haas also introduced low cost imidized acrylic polymer foams under the

trade names of KAMAX and Rohacell for commercial industrial and aerospace

insulation applications [96].

In 1986, High Technology Services, Inc. (HTS) of Troy, NY introduced poly(amic

acid) and polyimide based series of products and formulations, which were made from

BTDA and 3,3-diaminodiphenyl sulfone (DDS), based on NASA’s LARC-DDS

technology licensed from NASA and modified with siloxane containing diamines,

16

fluoro-elastomers and epoxy, such as series 1000 polyimide adhesives, series 2000X

poly(amic acid) based adhesives and series 2000X polyimide based adhesives. HTS

introduced TECHIMER line of BMI and Nadimide type of thermosetting product

formulations based on LARC-13. Bis-nadimide technology was licensed from NASA

Langley Research Center. TECHIMER-2001 was meant for microelectronics

application. It was a poly(amic acid) formulation which was converted to a thermoplastic

polyimide adhesive upon heating. [97-98].

In 1986, the High Performance Film Group of ICI Film Division of ICI America,

introduced a series of UPILEX Polyimide films (UPILEX R, UPILEX SX and

UPILEX X,) having comparable thermal, mechanical and electrical properties as that of

KaptonH (PMDA + ODA) and to compete with DuPont’s Kapton film business for

military and microelectronic applications. These products were based on biphenyl

dianhydride (BPDA) and m-PDA or ODA. Later this business was divested to Ube

Industries, Japan, which remained the sole manufacturer of the film [3-5, 12-13. 99-

100].

DuPont also introduced AVIMID-K brand series of polyimides which were

amorphous products obtained from monomer solutions by the reaction of diesterified

fluorinated dianhydride and aromatic diamines, for aerospace applications [3-5, 9-10,

20].

In 1987, National Starch and Chemical Co. USA introduced a series of thermosetting

acetylene-terminated polyimides (isoimide type) oligomers under the trade name of

THERMID IP 6000 as molding compounds. These isoimide oligomers upon thermal

curing converted to polyimides without releasing any by-products. This technology was

acquired from the Gulf Oil Co. in 1984. Later it introduced a series of fluorinated

17

versions under the trade name of THERMID FA 7000 for high temperature heat stable

materials for aerospace and engineering applications [23, 51].

In 1987, Hoechst Celanese Corp., RI, USA introduced SIXEF brand of series of

fully fluorinated polyimides, poly(amide-imide)s, photosensitive polyimides and

copolyimides in powder and formulation forms as high temperature advanced high

performance polymers for electronics, aerospace and gas separation membrane

applications. These polymers were based on fluorinated aromatic dianhydrides (6FDA

and 12FDA) and fluorinated aromatic diamines and other fluorinated, aromatic

monomers [11, 25-38,101-140] .

Figure-4: F-117, Stealth advanced tactical fighter (ATF) plane developed under DARPA funding by Lockheed, uses advanced polymeric materials based composites (US Air Force photo) [72]. From 1988 to 1991, Hoechst Celanese Corp., NJ, USA was a leading collaborator in a

team for the development of high temperature, high performance composite matrix resins

based on SIXEF-polyimide/polybenzimidazole (PBI) blends for low observable

supersonic advanced tactical fighter (ATF) plane (AT-71, a.k.a F-117)’s structural

components (Figure 4), under funding from NASA (Lewis) and DARPA. This team

18

involved scientists from major aircraft companies, (Boeing and Lockheed), as well as

major military aircraft engine manufacturer, (General Electric Engine Division), major

resin producer (Hoechst Celanese Corp SIXEF Polymers Group) and leading

universities (University of Massachusetts, MIT, Virginia Polytechnic, University of

Akron, and South West Texas State University) [26-28, 30-38, 101-140].

In 1987 Rogers Corp of. Chandler, Arizona and Rogers, Connecticut USA introduced

DURIMID brand high temperature poly(amic acid) and thermoplastic polyimide

formulation, DURIMID100 and DURIMID120, and powder products [141].

Ethyl Corp. introduced EYMYD brand of ultra-high 2,2-bis[4-(4-aminophenoxy)

phenyl] hexafluoropropane (BDAF) based fluorinated polyimide solutions for electronic

coatings. This low dielectric coating technology was originally developed by TRW, Inc.

and licensed to Ethyl Corp., USA [142-144].

Mitsui Toatsu Chemicals, Inc. of Japan licensed NASA’s LARC-TPI Technology, and

in 1988 introduced in all the countries except USA a REGULUS brand of polyimide

thermoplastic film products whose chemistry was based on BTDA and 3,3-diamino

benzophenone (a highly toxic and carcinogenic diamine). The films are biaxially oriented

which could be processed by thermoforming for electrical, and electronics applications

[145].

Chemiefaser Lenzing, AG of Austria introduced P84 Polyimide powders and strong

and ultra high tenacity fibers for non-flammable, thermally stable, high performance

mold and fiber braiding for aerospace composites application [146].

In 1989, Kanagafuchi Japan, and its US business partner Allied Signal, USA

introduced Apical PI Film, for electronic and microelectronic applications [12-13]

1990- 1995

In the USA alone, several companies introduced polyimide chemistry based products.

19

There were 63 products in the market. Many more companies around the globe

continued introducing more products and newer applications for electronic and

microelectronic. Besides, many Japanese companies introduced a series of ‘Negative’

and ‘Positive’ acting photosensitive polyimide product formulations for microelectronics

applications..

However, due to the end of the cold war and the collapse of Soviet Union, the R&D

efforts and funding for newer polyimides for aerospace and military applications has

slowed down drastically in the USA, with several companies withdrawing their

polyimide based products. Some companies went out of business altogether, and only a

limited number of companies continued marketing polyimide based products. By the late

1995 in the USA, about 35 products continued to cater to markets mostly in the

electronic and microelectronic and aerospace industries. However, worldwide

applications development for electronic and microelectronic end-uses continued at a

faster pace, and simultaneously the consumption of polyimide based products increased

for that industry sector [12-13, 52, 72].

1995 – 2000:

In 1996, Mitsui Toatsu Chemicals, Inc. of Japan introduced a liquid crystalline

polyimide (LC-PI) resin under AURUM brand name, which was originally known as

NEW TPI. It was based on another LARC-TPI Technology licensed from NASA. It was

advertised as a superheat resistant thermoplastic polyimide product whose chemistry was

based on pyromellitic dianhydride (PMDA) and 1,3-bis[4-(4-aminophenoxy) cumyl]

benzene (BAPCB). The polymer can be molded into complex engineering parts, wire

extrusion coatings, and film/fibers for automotive, electrical, and electronics applications

[147].

20

1.1.2.3. Brief summary of polyimide market size and growth projection (years 2000 to 2010) Approximate 9.15 million kg of polyimide (US $ 442 millions) was produced in 1995,

and in 2000, it was 14.78 million kg (US $ 1087 millions), which represented an increase

of about 10.05 % per year through 2000. The major portion of the market share (about

40%) was covered by the electronics industry’s usage of specialty polyimide based films

and photosensitive products, whereas the engineering and aerospace industries combined

covered the rest. Among these, polyetherimides (PEI) represent the largest market with

around 2.9 million kg valued at about US$ 50.00 millions. These applications include

connectors, flexible circuit board, IC-packaging, sockets, lead-chip carriers, etc. Also

included were the medical appliance applications, such as humidifier manifold, surgical

lights and sterilization apparatus, etc.

The price for large volume, low margin polyimide products for engineering

applications was in the range of US$ 8.50 to 185 per pound (~US$ 18.75 to 400 per kg),

whereas for small volume, high margin electronic application products it was in the

range of US$ 65 to 580 per pound (~ US$ 145 to 1275 per kg) on dry neat polymer basis

[3-7, 9, 20, 72].

Research cut back continued, but worldwide demand for polyimide polymers went up.

In 1997 it was estimated that polyimide usage topped approximately 12.78 million kg

valued at over ~US$ 900 millions. It will continue to grow at a moderate rate.

Due to recent world wide economic downturn, the market projections were revised.

Unless the economic condition improved, it was estimated to continue to grow at a

slower rate. By the year 2010 it may grow to a staggering 23.43 + million kg or about

~US$ 2160 millions in value.

For the various polyimide based products, the market sector for polyimide films for

electrical and electronics and commercial applications as well as ‘photosensitive’

21

polyimide formulations for microelectronics applications was also estimated to continue

to grow at a reasonably steady rate of 5 to 8 % to year 2010 [Table 3]. Market growth is

expected to triple for electrical and electronics applications and double for aerospace.

Since 1990, NASA has joined Boeing Company, GE Aircraft Engines, McDonnell

Douglas and Pratt & Whitney (Aircraft Engines) to initiate the High-Speed Research

(HSR) Program. The goal is to continue research and development of the critical

technology needed for an environmentally compatible and economically viable High-

Speed Civil Transport (HSCT) airliner (Figures 5 and 6). This program continues to be a

high priority for NASA and is intended to enhance the technology for the world’s next

generation of commercial aviation industries by the year 2015 [148-149].

Table-3: Polyimide market growth projection.

YEAR 1998* 2000** 2010** Polyimide Products MM kg MM $ MM kg MM $ MM kg MM $ Film 0.868 155.00 0.951 172.00 01.756 320.0 Photo-sensitive 0.293 387.00 0.302 400.00 00.744 1000.0 Molding Compd. 8.099 170.00 8.265 175.00 12.50 270.0 Coating &Adhesives 4.546 235.00 4.959 270.00 7.851 430.0 Foam 0.124 054.00 0.145 063.00 00.257 126.0 Fiber 0.132 005.80 0.161 007.08 00.331 014.5 Total 14.062 1006.8 14.783. 1087.08 23.433. 2160.5.

MM kg = Million kilograms; MM $ = Million US $; * : [3-6, 9, 20]; ** : [7, 9] Especially, due to increasing demand for lighter and stronger materials, which can

withstand high operating temperatures, particularly in military and commercial

supersonic transport planes, aerospace (rockets and space shuttles), microelectronic fab

processes, oil-field gas separation membranes, etc., the chemistry of polyimides will

continue to be at the forefront of polymer science research and development worldwide

[3-7, 9, 12-13, 20, 52].

1.1.2.4. Brief summary of literature survey on worldwide polyimide R&D activities

It is noteworthy to mention here that currently extensive research is being carried out

22

in the polyimide area around the globe in universities and in multinational companies.

These research projects involve basic and applied polyimides R&D. Numerous books,

reviews, papers and patents have been published on the synthesis, structure, properties,

characterization and applications of polyimides [2, 14, 16, 44, 51, 58, 150-160] and

several international conferences on polyimide have been held regularly since 1982 [161-

164].

Figure-5: Artist’s concept of future hypersonic commercial jetliner of Boeing Co [148].

Figure-6: Artist’s concept of high-speed civil transport plane of McDonnell Douglas Co, [149].

23

Statistical data derived from the Chemical Abstracts (ACS) [165-166] search showed

that since 1950, over 49000 scientific works on polyimides have been published, with

3100 scientific works on polyimides published during 1992-1997, whereas the number

was 1600 during 1987-1991. This means that during those five years there was a two-

fold increase in the publication of polyimide literature.

CA Select-Polyimide (ACS) search revealed that for the 12 month period in 1997 - 98

[165] in the USA alone, 105 universities and 100 companies combined had 308

publications and 95 patents filed. Industries led in filling patents with equal number of

publications, whereas, universities led in publications, as illustrated in the Table 4.

Table-4: Polyimide R&D in the USA in the 12 month period between August 1997 to July 1998. [165]

ENTITY PUBLICATIONS PATENTS OTHERS UNIVERSITYY 106 220 14

COMPANY 100 88 75 38

IBM

Followed by DuPONT INDIVIDUAL 6 6 6

NASA Followed by Virginia Polytech

COMPANY PATENTS PUBLICATIONS TOP UNIVERSITY PATENTS PUBLICATIONS 1) IBM 11 30 1) NASA (R&D) Institution 4 32 2) DuPont 6 3 2) Virginia Polytech & State U. - 31 3) Xerox 5 - 3) U. of Akron - 21 4) Air Products 4 4 4) Georgia Tech. - 14 5) GE 4 8 5) U. of Texas - 12 6) Texas Instruments 4 1 6) College of William & Marry - 10 7) U. of California 1 9 8) Lawrence Livermore Nat. Lab - 6

In the same period, the total number of publications on polyimides worldwide was

1365, of which 1104 were from the academic institutions. Besides there were 1208

patents issued, in which over 95% were granted to industries as illustrated in Table 5.

Even today, Japan continue to maintain its leading edge in polyimides R&D for

electronics application, and polyimide based products manufacturing for

microelectronics industries, implying that polyimide is still a highly valuable polymer

business [6-7, 165].

Even in the three year period from January 1999 to December 2001, there were .8280

publications and 4643 patents issued in polyimides and related R&D work. During the

Industrial research lead equally in filling patents and publications while Universities lead in publications

24

last 10 years there have been 135 publications in the new emerging field of polyimide

hybrids and polyimides nanocomposites.[6-7,166] However, there was interesting

growth in these area of research with increasing number of publications and issuance of

patents in the same three years time frame as shown in Tables 6 to 8 [6-7,166].

Table-5: Worldwide polyimide during the 12 months period between August 1997 to July 1998 [165].

UNIVERSITY COMPANY INDIVIDUAL No.

COUNTRY

No. of

U.. PUB.

PAT. No. of

Co. PUB.

PAT. No. of

Indv.. PUB.

PAT.

TOTAL

OTHERS

1 AUSTRALIA 7 8 8 2 AUSTRIA 5 8 2 2 10 3 BULGARIA 9 12 1 1 13 4 CANADA 10 23 3 2 2 1 1 27 1 5 CHINA 41 101 101 6 CZECH REP.. 4 6 6 7 FINLAND 2 2 4 2 2 6 1 8 FRANCE 25 34 2 5 1 11 3 3 51 1 9 GERMANY 49 68 25 7 28 4 4 107 14 10 GREEC 3 9 9 11 HONG KONG 2 6 6 12 HUNGARY 3 3 1 2 1 1 6 13 INDIA 15 28 3 3 31 143 ITALY 11 14 4 3 1 18 15 JAPAN 56 276 5 235 97 1016 12 12 1406 58 16 KAZAKHSTAN 2 9 1 1 10 17 KOREA S. 25 77 6 12 12 89 12 18 THE

NATHERLANDS 5 13 4 3 4 20

19 POLAND 7 7 1 1 1 9 20 RUMANIA 6 9 2 11 21 RUSSIA 43 70 10 1 1 8 7 1 89 22 SINGAPORE 2 8 1 1 9 23 SPAIN 9 12 12 24 SWITZERLAND 4 4 4 4 1 9 25 TAIWAN 15 40 2 2 42 26 UK 15 19 8 6 2 6 6 33 6 27 USA 105 220 14 100 88 75 6 6 403 38 OTHER 16 18 2 2 20

TOTAL 496 1104 34 411 237 1154 44 24 20 2561 131 PUB. : PUBLICATIONS: PAT. : PATENTS

Table-6: Statistics of research publications and patents on polyimides (1999-2001) [166]

POLYIMIDES

Since 1950, reported total worldwide publication : 49651

Last three years statistic of R&D activities

Year Publications Publications 1999 2885 1511 2000 2852 1709 2100 2543 1423

TOTAL 8280 4643 During last 15 years, there have been tremendous interest generated in the ‘Nano-scale’

materials R&D and technology development, due to which several publications started to

appear. During the last 10 years several polyimide hybrids with inorganic materials and

25

polyimide–clay nanocomposites with improved thermal and mechanical properties have

been reported.

Table-7: Statistics of research publications and patents on polyimide hybrids (1999-2001) [166]

POLYIMIDE HYBRIDS



Year Publications Publications 1999 15 1 2000 18 5

2100 28 11 TOTAL 61 17

Table-8: Statistics of research publications and patents on polyimide/clay nano-composites (1999-2001) [166].

POLYIMIDE NANOCMPOSITES



Year Publications Publications 1999 14 2 2000 32 16 2100 45 21 TOTAL 91 39

1.1.2.5. Types of polyimides

There are three types of polyimides: (i) Condensation, (ii)) Addition, and (iii) Linear

oligomeric, terminated with crosslinking groups [14]. Examples of these polymers are

given in Table 9.

The first type depends on the traditional reaction route between a dianhydride and a

diamine in two steps, i.e., the dianhydride reacts with the diamine to form poly(amic

acid) in the first step, which is usually soluble, followed by imidization (second step)

through a thermal curing at temperatures above 300°C or by chemical means. The

second type is based on the addition reaction of monomeric di-imides to other

compounds (e.g. monomers) terminated with vinyl groups. During these reactions there

26

are no by-products released. The third type is based on the condensation polyimide route

to produce an oligomeric linear polyimide which then reacts with compounds

terminating in a crosslinking group, an amine, or a carboxylic acid group. Such

polyimides are soluble, thermoplastic, and can be crosslinked at elevated temperatures

via the crosslinking groups. NASA’s polyimide PMR-15 series belong in this category

[152].

Table -9: Types of polyimides:

Condensation Type: o Thermosets: Based on

o PMDA/ODA chemistry o BTDA/MDA chemistry o Non-photo sensitive chemistry o Photosensitive chemistry

o Thermoplastics: based on

o Polyetherimides chemistry o BTDA/TDI/MDI chemistry o Avimide K and N chemistry o LaRC-TPI chemistry o BTDA/DAPI chemistry o Polyimide sulfone chemistry

Addition Polymerization Type: based on

o Crosslinkable chemistry o PMR-15 chemistry o Acetylene terminated chemistry o Bismaleimide chemistry o Bisnadimide chemistry

Recently, aromatic polyimides [2, 9, 16, 28], fluoropolyimides [2, 9, 11, 16, 26-

38,101-138, 167-172], liquid crystalline [173], and oligomeric polyimides [174] and

their blends [138] have become one of the most prominent and important polymers in the

advanced polymer categories. A large number of starting monomers and polyimides with

different structures have been synthesized. In this respect, an industry was created for the

production of polyimide materials for various applications.

The literature search revealed that polyimide chemistry was well established, and

polymers were synthesized by various methods, some of which were practiced

27

commercially. A brief discussion of current synthesis methods, structures, properties and

applications of polyimides is given below.

1.1.3. Synthesis of polyimides

Polyimides are polymers containing an imide linkage either as an open-chain structure

or as a heterocyclic unit in the polymer backbone (Figure 7). Only a few articles dealing

with polyimides with the open-chain imide linkage have been reported [174]. In contrast,

the synthesis and characterization of aromatic polyimides have been extensively reported

in the literature. Numerous papers and books devoted to synthesis and applications of

polyimides with heterocyclic units have been published since the first report of

polyimide in 1908 [14, 16, 51, 175-176]. The preparation of polyimides by reaction of

aromatic dianhydrides with aromatic diamines followed by thermal cyclization was

reported from 1955 to 1970 [40-44, 51-68, 178-181].

However, polyimides have been more rapidly developed, since the first commercial

polyimide product, Kapton, was successfully introduced into the market [14, 16, 51].

R C N C

O R O

n

C

C

O

O

N Rn

Figure-7: Types of polyimide structures

In general, the polyimides are aromatic compounds containing an imide with five-

member ring units and aromatic rings in the repeat unit, which forms part of the most

popular and important high-performance polymeric materials. As mentioned earlier, there

are three kinds of polyimides: condensation, addition and linear, terminated with

crosslinkable groups. From the first invention of aromatic polyimides to the synthesis of

new thermoplastic polyimides with excellent performance, it has been shown that the

successful application, processing and outstanding properties of polyimides are closely

28

associated with the synthesis of polyimide resin. Hence, synthesis forms the cornerstone

for polyimide chemistry.

1.1.3.1 Monomers

A large number of starting monomers are reported in the literature and numerous

patents. Most of them are aromatic compounds and are available commercially in small to

large quantities. Some are produced for captive consumption. The generic structures of

these monomers are given in Figure -8.

Figure-8: Generic structures of aromatic dianhydride and diamines

Figures 9 & 10 below show the chemical structures and abbreviations of diamine and

dianhydride monomers currently used in the synthesis of polyimides of interest. Most of

these monomers are available commercially at a price in the range of US$ 50.00 to

125.00 per kg except most fluorinated monomers, as they are extremely expensive,

especially the diamines (price estimated to be > ~US $ 1775.00/kg). Electronic grade

6FDA is available at US $ 500.00 per kg in small quantities [6-7]. In commercial

quantities, the price would be much lower. However, the use of fluorinated monomers is

AC

OCC

OC

O O

O O

Aromatic Diamines

AND / OR

Aromatic Dianhydride

A2A1

A4 A3

XA1 A2

A1 A1

A3A4A3 A4

A1

A3

A2

A4

AND / OR

Where X = Single bond, -CH2-, -O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

, etc.

Where A = OR

-Si(CH3)2-O-Si(CH3)2-,

Where Y= X

XA1 A1

A2A2

A1

A2

Y OO

A2 A1 A1 A2

A4A3A3A4

A1

A3

A2

A4

,

Where X = Single bond, -CH2-,-O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

, etc.

Where Z = X


Z OO

A2 A1 A1 A2

A4A3A3A4

C

A2A1

A4 A3

CH3

CH3

CCH3

CH3

,,

CC

A2A1

A4 A3

O O

Where A1 A2 A3 A4 OR A1 A2 ,

OR A3 A4 ,OR A2 A3 ,A3 , A4 , OR A1 OR A1

Where A1, A2, A3, and A4 could be H, -CH3 , -CH3(CH2)n ; where n = 1 to 20, -NO2 , -OH , -I , -Br , -Cl , -F , -NCO ,-COOH , -CN , -CNO, -CF3 , -C6H5 ,

-(CH -(CCH2) , CH) , etc.

OR A2 A4 ,

AC

OCC

OC

O O

O O

Aromatic Diamines

AND / OR

Aromatic Dianhydride

A2A1

A4 A3

XA1 A2

A1 A1

A3A4A3 A4

A1

A3

A2

A4

AND / OR


, etc.

Where A = OR


Where Y= X

XA1 A1

A2A2

A1

A2

Y OO

A2 A1 A1 A2

A4A3A3A4

A1

A3

A2

A4

,

Where X = Single bond, -CH2-,-O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

, etc.

Where Z = X


Z OO

A2 A1 A1 A2

A4A3A3A4

C

A2A1

A4 A3

CH3

CH3

CCH3

CH3

,,

CC

A2A1

A4 A3

O O

Where A1 A2 A3 A4 OR A1 A2 ,

OR A3 A4 ,OR A2 A3 ,A3 , A4 , OR A1 OR A1

Where A1, A2, A3, and A4 could be H, -CH3 , -CH3(CH2)n ; where n = 1 to 20, -NO2 , -OH , -I , -Br , -Cl , -F , -NCO ,-COOH , -CN , -CNO, -CF3 , -C6H5 ,

-(CH -(CCH2) , CH) , etc.

OR A2 A4 ,

29

the most effective way to obtain high performance thermally stable polyimides with low

dielectric constant for electronic applications.

The purity of the monomers is very critical in obtaining polyimides with high

molecular weight and good electrical properties. Most of these monomers are available

with purity in the range of 98.5 to 99.8% with trace impurities of sodium, potassium,

iron, and chloride in ppm level. It is, therefore, typically a necessity to purify these

monomers by re-crystallization, vacuum distillation or by sublimation. These monomers

are then kept in an inert environment and dried one or more times prior to use.

C C

C

C

CF3

O CF3 O

O

OCO

C

C

CO

O

O

OC

O

C

C

CO O

O

OCO

CO

C CO

CCO

O O

OO

CO

C CO

COO

O O

O

O

O

PMDA

6FDA

BPDA

O

BTDA

ODPA

CO

C CO

CSO

O O

O

DSDA

O

O

Si C

C

C

CH3

O CH3 O

O

OCO

O

Si DA

CO

C

O

O

O

CO

C

CCO

O

OO

CO

C

O

O

IPDA

CO

C

O

O

S O

CO

C

O

O

O

CO

C

O

O

C O

CH3

CH3

BPADA

BDSDA

Figure-9: Dianhydride monomers structures with their abbreviation used for preparing polyimides

1.1.3.2. Polyimides by polycondensation [14, 16, 51, 151-152]

Polymerization (synthesis) reaction is a complex reaction requiring a careful control of

30

various reaction parameters to achieve high molecular weight polymers. The

polymerization reaction described as below can be obtained by the condensation of two

monomers in equi-molar ratios: typically a dianhydride and a diamine with the

elimination of small molecules e.g. water as shown in Figure 11. The reaction kinetics

could be enhanced by use of a condensation catalyst. However, thermal and chemical

imidization methods are predominantly used commercially.

NH2H2NH2N NH2

O

O

H2N NH2

H2N NH2

OH2N NH2O

OH2N NH2O

O

NH2

H2N

SH2N NH2CH2N NH2

SH2N NH2

O

O

O

H2CH2N NH2

CH2N NH2

CH3

CH3

CH2N NH2

CF3

CF3

C

CF3

CF3

H2N NH2

H2N NH2

Si O Si (CH2)3 NH2(H2C)3H2N

CH3

CH3

CH3

CH3

mPDA pPDA3,3'-ODA

4,4'-ODA3,4'-ODA

4,4'DDS

4.4'DDSO

4,4'-BPD

MDA

IPD

4,4'-6F-DAM 3,3'-6F-DAM

4,4-APB

4,4'-(1,3)-APB

DPTP

1,3-SiDAM

OH2N OC

4,4'-BDAF

NH2

CF3

CF3

OH2N OC

4,4'-BPADE

NH2

CH3

CH3

Figure-10: Diamine monomers structures with its abbreviation used for preparation of polyimides.

31

C

Q

C

CC

OO

O O

OO H2N R NH2

C

Q

C

CC

OO

O O

OOHN R

C

QC

CC

OO

O O

NN R

HN

OHHO

+

n

n

Thermal Imidization OrCatalyst -2H2O

Dianhydride DiaminePoly(amic acid)

Polyimide Figure-11: Polyimide from a dianhydride and a diamine 1.1.3.2.1. Polyimides from dianhydrides and diamines [14, 16, 51, 177]

The preparation of polyimides from dianhydrides and diamines is the most popular

and more traditional method for conventional polyimides and thermoplastic polyimides

synthesis. The reaction proceeds in two steps. The first step leads to the formation of the

intermediate, poly(amic acid) from the reaction between a dianhydride and a diamine,

which is then imidized (second step) by heating at elevated temperature (300°C) or

chemically. The first commercial polyimide, Kapton, was produced from PMDA and

4,4-oxydianiline (4,4-ODA) by this route as shown in Figure 12 [58-59, 180].

C

O

C

O

O

NH2OH2N+HN

n

[PMDA+4,4-ODA] Poly amic aci)4,4 Oxydianilina ( 4,3-ODA)

C

O

OC

OPMDA

C

O

C

O

C

O

C

O

O

N

n

C

O

C

N

O

C

O

C

O

O

OHHO

HN

-2H20

Kapton [PMDA+4,4-ODA] Polyimide

Thermal Imidization

Figure-12: The first commercial polyimide, Kapton, production route [58-59, 180].

There are a few advantages of this method when compared to other methods available

for preparing polyimides. One of them is the better solubility of dianhydrides in an

organic solvent than that of the tetra-carboxylic acid, or the intermediate poly(amic acid).

Besides, the choice of dianhydrides is also more. The drawbacks of this method are the

32

sensitivity to moisture (water), unstable viscosity of poly(amic acid), and the release of

by-products e.g., water during imidization. Hence, this method is only suitable for thin

products such as films, fibers, and coatings, and it is not suitable for thicker items, such

as molding, laminating and packaging materials.

However, it is a common observation of many experienced polymer chemists, [14, 16]

that the viscosity, both bulk and inherent (hence the molecular weights) of the poly(amic

acid), for example in classical case of [PMDA+ODA] system in NMP, would increase

slightly at the room temperature storage for a few days initially, but would gradually

decrease considerably. It is, therefore, well known that the poly(amic acid) (PAA) is

unstable over a period of time in solution form at room temperature, as well as at an

elevated temperature. Its molecular weight would decrease depending upon the condition

in which it is stored and the type of solvent used. It also depends on the purity and the

moisture content of monomers and solvent used and the interaction (bonding and de-

bonding) of the free end groups of the polymer backbone. This has been attributed to the

fact the NMP complexes (hydrogen bonding) with the polyamic acid in the early stage of

the storage. Thus a gel-like structure formation and pseudo-bulk viscosity increase is

observed. But as time passes, the moisture in the solvent hydrolyzes the weak hydrogen

bond formed with NMP as well as amide acid bonds. These results in decrease in

molecular weight and a lower viscosities [2, 14, 16, 152,174, 181].

1.1.3.2.2. Chemical mechanism of polymerization reaction

The kinetic studies show that the reaction of formation of poly(amic acid) by this

method is fast and exothermic, and is strongly affected by the structure and purity of

monomers (dianhydride and diamine), temperature, concentration, polarity and purity of

solvents and the presence of impurity (moisture and metal ion) [14,16, 51,151,182].

33

Therefore, the initial reaction of the formation of poly(amic acid) is always carried out

below 20 oC for obtaining polyimides with a higher molecular weight [11, 182].

The chemical mechanism pathway of the above reactions may be explained as follows.

It is well described in the literature [14, 16, 174] that about five types of concurrent

reaction kinetics steps take place during and after the first few hours of poly(amic acid)

synthesis.

These 5 major reaction steps[14] are:

• Acylation of amine with anhydride (chain propagation step)

• Spontaneous cyclization of amic acid groups with the elimination of water and

formation of imide rings (chain growth termination and equilibration (averaging) of

chain lengths)

• Hydrolysis of amide bonds and formation of free amine and free carboxylic acid

groups. (chain growth termination )

• Hydrolysis of terminal anhydride groups and formation of dicarboxylic acid groups

(chain growth termination)

• Cyclization with elimination of amine and formation of anhydrides ring (scission

within chains) leading to di- and tetra-acids. Which reverse reaction and re-

equilibration of chain lengths.

These five major polymerization reactions kinetics are illustrated in Figure 13.

One can explain that during the early stage of reaction, both the weight-average

molecular weight ( wM ) and number-average molecular weight ( nM ) increase rapidly,

arising from chain propagation and hydrolysis of terminal anhydride groups. After this,

the molecular weight decreases due to spontaneous hydrolysis of amide and cyclization

of ortho-carboxy-amide groups with elimination of the amino group. The ortho-carboxy-

amide group of the poly(amic acid) structure is capable of cyclization to form imide,

34

isoimide, or anhydride rings. A carboxyl group in the ortho- position to an amide bond

can intra-molecularly catalyze the cleavage of this bond, leading to chain scission.

Intermolecular cyclization and degradation proceed spontaneously. Also the water

content in the solution increases the hydrolysis of the excess anhydride, leading to the

formation of excess free dicarboxylic acid groups and free amines. This then leads to

chain growth termination. It is also possible that ionic bond formation occurs between

the free acid groups and free amines, which may lead to instability of the viscosity.

Therefore, an increase in solid concentration, high purity of monomers and lowering the

water content of the solvent are desirable for higher molecular weight and stable

viscosity of poly(amic acid) [14, 16].

Figure-13: Five key polymerization reaction kinetics to consider and control during synthesis of high molecular weight poly(amic acid) [14]. The nature of solvent affects the conformational characteristics of poly(amic acid)

especially in the weak base type solvents e.g., NMP. The ortho-amic acid a relatively

strong carboxylic acid. It is because of the electron withdrawing effect of the ortho-

X

C+ H2N

k1

( 1 )

C X C

C

OOH

O

HN

O

O

O

k2H2O

( 2 )

X C

C

OOH

O

HN

X

C+

CO

O

N

k3

+ H2N

( 3 )

+ H2OX

CHN

C X C

C

OOH

OOH

O

O

OHk4

( 4 )

X

C+

CO

O

O H2OX C

C

OOH

OOH

k5

( 5 )

X C

C

OOH

O

HN

X

C+ H2N

CO

O

O

Acylation of amine with anhydride (chainpropagation step)

Spontaneous cyclization of amic acid group with theelimination of water and formation of imide rings(chain growth termination and averaging of chain lengths)

Hydrolysis of amide bonds and formation of free amine free carboxylic acid groups (chain growth termination)

Hydrolysis of terminal anhydride groups and formation of dicarboxylic acid groups (chain growth termination)

Cyclization with elimination of amine andformation of anhydrides ring (scission withinchains) leading to di and tetra - acids. Chainlengths averaging due to Reverse reaction.

C OH

CC

C

CCF3

CF3

O

O

O

OHO

NH A

n

NH

Fluoro-poly(amic acid)[in 15-25% NV in Dipolar Aprotic Solvent]

Where X and A are defined in Figure 8

X

C+ H2N

k1

( 1 )

C X C

C

OOH

O

HN

O

O

O

k2H2O

( 2 )

X C

C

OOH

O

HN

X

C+

CO

O

N

k3

+ H2N

( 3 )

+ H2OX

CHN

C X C

C

OOH

OOH

O

O

OHk4

( 4 )

X

C+

CO

O

O H2OX C

C

OOH

OOH

k5

( 5 )

X C

C

OOH

O

HN

X

C+ H2N

CO

O

O

Acylation of amine with anhydride (chainpropagation step)

Spontaneous cyclization of amic acid group with theelimination of water and formation of imide rings(chain growth termination and averaging of chain lengths)

Hydrolysis of amide bonds and formation of free amine free carboxylic acid groups (chain growth termination)

Hydrolysis of terminal anhydride groups and formation of dicarboxylic acid groups (chain growth termination)

Cyclization with elimination of amine andformation of anhydrides ring (scission withinchains) leading to di and tetra - acids. Chainlengths averaging due to Reverse reaction.

C OH

CC

C

CCF3

CF3

O

O

O

OHO

NH A

n

NH

Fluoro-poly(amic acid)[in 15-25% NV in Dipolar Aprotic Solvent]

Where X and A are defined in Figure 8

35

amide group and its stabilization by internal hydrogen bonding of dissociated

carboxylate with amide hydrogen. The strong acid-base interaction between the amic

acid and the NMP solvent is the major source of the slight increase in the exotherm of

the reaction and one of the most important driving forces for the complex spontaneous

reactions leading to imide rings formation and water generation. In the presence of water,

the anhydride groups are hydrolyzed to give free dicarboxylic acid groups. The reaction

is driven by the nucleophilicity of water in dipolar, aprotic solvent and by strong acid-

base interaction of the products of these spontaneous reactions with the dipolar solvent.

[16, 174]

1.1.3.2.3. Chemical imidization reaction

Imidization of poly(amic acid) (second step), may be accomplished chemically or by

heating at elevated temperatures (300oC).

The dehydration system of acetic anhydride-tertiary amine is a very effective system

for imidization of poly(amic acid) at room temperature. Poly(amic acid) has good

solubility in organic solvents, and in general, the polyimides prepared by chemical

imidization method possess better solubility in organic solvents than those prepared by

heating at elevated temperatures, because the side reactions are suppressed under the

mild reaction conditions (chemical imidization) [14, 16].

1.1.3.2.3.1. Mechanism of chemical imidization

The literature on chemical imidization kinetics is not much. But it is now established

that the cyclization of n-phenylphthalamic acid of the polymer segment with acetic

anhydride proceeds smoothly at room temperature in NMP in the presence of a tertiary

amine [14, 16, 68, 183].

Other dehydrating agents such as propionic anhydride, n-butyric anhydride, benzoic

anhydride etc. may also be used. Typically, triethyl amine, β-picoline, pyridine,

36

methylpyridines, lutidine, N-methylmorpholine, etc are used as tertiary amines. The

amine acts as a catalyst as well as an acid acceptor. The acetic anhydride acts as a

dehydrating agent. Each mole of water liberated due to dehydration converts acetic

anhydride into two moles of acetic acid. The phthalimides are formed by intramolecular

nucleophilic substitution at the anhydride by amide nitrogen atom. There is also the

possibility of the formation of isoimides by the substitution by the amide oxygen.

However, under the close analysis the mechanism of chemical imidization is found to be

quite complex, and depends on the type of dehydrating agents, monomer components,

solvent and reaction temperature employed [16, 183]. Typical reaction mechanism steps

are given in Figure 14.

A4

A1 A2

A3

NH2NH2C

OCC

OC

XO

O

O

O

A4

A1A2

A3

CN

CCN

C

XO

O

O

O

A4

A1A2

A3C OH

CC

C

XO

O

O

O

HO

HN

CH3CO

OC

OH3C

A4

A1 A2

A3C

O

CC

C

XO

O

O

OO

HN

CO

CH3CO

H3CA4

A1A2

A3C OH

CC

C

XO

O

O

O

HO

HN

+n

+ NR3

n + 2 [CH3COO HNR3]n +

A4

A1 A2

A3C

O

CC

C

XO

O

O

OO

HN

CO

CH3CO

H3C

nA4

A1A2

A3

CO

CC

C

XO O

O

N

CO

CH3CO

H3C nOO

nA4

A1A2

A3C

O

CC

C

XO O

OH

N

CO

CH3CO

H3C

n

O

N

O

N

H.

H.H.

H.+

Poly(amic acid)Aromatic Dianhydride Aromatic Diamine

Tertiary Amine Base &Organic AcidAnhydride

Tertiary Amine - Acetic Acid Salt

Ionic complex intermediate compound

Poly(amic acid)

Ionic complex intermediate compound Polyimide

2 [CH3COO HNR3]

Where X, A1, A2, A3 & A4 are defined in Figure 8

(-2 H2O)

Figure-14: Typical mechanism of chemical imidization of poly(amic acid) to polyimide [14, 16] It should be noted that the control of molecular weight is very important for preparing

high performance polyimides. It has been shown, for example, in Table 10, that the

presence of moisture, impurities, side reactions, purity of monomers, reaction

temperature, reaction period, monomer quantities, and the molar ratio of dianhydride to

diamine are affect the molecular weights of polyimides synthesized. Obviously,

37

impurities such as a chain stopper in the reaction system usually affect the kinetic chain

length, while moisture (water) converts dianhydride into tetra-carboxylic acid, thus

reducing the reactivity of the dianhydride. In general, the higher the temperature, the

lower is the molecular weight. This is associated with the formation of more reactive

centers at higher temperatures, thereby leading to a shorter kinetic chain length. The

reaction temperature at 20 oC or below is optimal. It is very important to control the

molar ratio of dianhydride to diamine, as even a slight excess of dianhydride or diamine

will reduce the molecular weight to a considerable extent, as illustrated in Table 11.

Metal ion such as iron may also convert diamine to monoamine during the reaction or

upon storage. Monoamine is a chain stopper and may limit the increase of the kinetic

chain length.

Table-10: Effect of molar ratio of monomers on the molecular weight of a polyimide* [152]

Dianhydride

(molar)

Diamine

(molar)

Molar excess Molecular weight

( nM )

1.02 1.00 2% 38500

1.01 1.00 1% 48500

1.00 1.00 0% 57000

1.00 1.01 1% 46000

1.00 1.02 2% 37000

*: [PMDA + ODA] poly(amic acid) synthesis reaction was carried out in the DMF solvent The main side reactions in polyimide synthesis between a dianhydride and a diamine

are given in Figure 15:

Hydrolysis and exchange reactions are responsible for the degradation of poly(amic

acid). The presence of carboxylic acid in the poly(amic acid) solution has a catalytic

effect and may accelerate the hydrolysis and exchange reactions [16]. In order to obtain

better performance from polyimides, improvements have been made in the dianhydride

route. This has led to numerous high-performance polyimides e.g. thermoplastic

38

polyimides, fluorine-containing polyimides, silicone polyimides synthesized by using

different combinations of monomers. The chemical structures of dianhydride and

diamine monomers used for preparing polyimides are shown in Figures-9 &10.

Figure-15: Possible side reactions that may occur during poly(amic acid) synthesis in NMP [14, 16, 174]. Soluble polyimides can also be prepared by high temperature (140-250 °C) solution

polycondensation in a one-step reaction using para-toluenesulfonic acid (p-TSA) as

condensation catalyst and halogenated aromatic solvents or mixture thereof. [18-19].

Research work has revealed that the imidization reaction in polyimide synthesis begins at

120 °C, but is completed over 300 °C. Hence, there are some difficulties in controlling

the molecular weight of the final product at such high temperatures.

1.1.4. Fluoro-polyimides In 1988 Cassidy and coworkers at the South West Texas State University, TX, USA

carried out an extensive review of fluoro-polymers with the financial support from

Hoechst Celanese Corp. USA. [185]. This report was extensive and had a well

documented data base on fluoro-polyimides of that time reported in numerous technical

C

C

OHOH

O

O

C

C

O

O

O H2O

NO

CH3

COOHNHCH3

H2O

C

C

OHNH

O

O

C

C

NHNH

O

O

H2N

+

+

+

C

C

OHNHA

O

O

C

C

OHNHCH3

O

O

H C

O

N(CH3)2H C

O

NA(CH3) ++

C

C

OHNH

O

O

C

C

OHOH

O

O

NH2H2O+ + (Hydrolysis)

(Exchange)

39

papers, conference papers and patents. Even today this report would serve as a valuable

resource to those who would like to venture into fluoro-polymers R&D. Because of the

limitation of space in this chapter, the focus has been on only a few selected fluoro-

polyimides that had been commercialized [186-215] in the last 15 years, and are briefly

reviewed and reported here.

During the past three decades, interest in the polyimide technology has increased in

response to an increasing variety of applications in numerous technologies varying from

aerospace to medical to microelectronics. However, due to the limited solubility of some

of the conventional polyimides in common organic solvents, several well-directed R&D

efforts were made by high performance polymer companies and in universities world-

wide. Various polyimides with perfluoroalkyl groups have been investigated for their

commercial applications.

One of the most attractive and successful attempts in attaining good solubility of

conventional polyimides for easy fabrication was demonstrated by Rogers et al. at

DuPont Co. in the USA [189], and Critchley at UK Govt.’s defense department research

laboratories in the UK [190] through the introduction of perfluoroisopropylidene groups

e.g., 1,1,1,3,3,3-hexafluoroisopropyl (HFIP), into the polymer chain backbone via

dianhydride structure [25-28]. The hexafluoroisopropylidene bridged dianhydride was

developed and identified as 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane

dianhydride, and became better known as 6FDA. Later it was also discovered that the

inclusion of hexafluoroisopropylidene group in the amine portion of the polymer chain

also imparted similar solubility [191]. The following two new hexafluoroisopropylidene

bridged diamines were reported by Dupont, and a series of fluoro- polyimide products

based on these diamines and developed by Vora were commercialized under the trade

name SIXEF by Hoechst Celanese Corp., RI, USA [25, 25-31, 185].

40

o 2,2-bis(3-amino phenyl) hexafluoropropane, i.e. (3,3-6F-Diamine)

o 2,2-bis(4-amino phenyl) hexafluoropropane, i.e. (4,4-6F-Diamine)

DuPont also developed and marketed NR-150 formulations based on 6FDA and ODA

which showed excellent high temperature adhesion properties but were difficult to

process because of the presence of condensation volatiles and high boiling solvent

residue [185-186]. These fluoro-polyimides exhibit high thermal stability, i.e., they retain

usable properties at 300°C for months and can even withstand temperature > 500 °C for

a few minutes. Some fluoro-polyimides having hexafluoroisopropylidene groups in both

monomers showed optical transparency far greater than conventional polyimides

(>70%). These thermally stable polymers transmit solar radiations without appreciable

degradation and find application as coating materials to protect solar cells from the solar

radiation damage [187-191].

Landis and coworkers [196] at Huges Aircraft Co. in Ohio, USA reported acetylene-

terminated imide oligomers having improved solubility and lower melting points

synthesized from 6FDA and aromatic diamines and end capped with (aminophenyl)

acetylene. These are thermosetting type polymers and useful as molding compounds for

military, aerospace and engineering applications [200]. Later Harris [201] and coworkers

at the University of Akron, OH, USA reported a series of polyimide oligomers

terminated with thermally-polymerizable groups in a project for Gulf Oil Co. [201-202].

These materials later were commercialized by National Starch & Chemical Co. NJ, USA

under the trade name THERMIDFA 7000 [9, 12-13, 51].

Fluoro-polyimide foam has been reported by Imitec Inc., which was prepared by the

reaction of 3,3,4,4-benzophenone tetracarboxylic acid dimethyl ester and 4,4-6F-diamine

using microwave energy. The foams have closed cells, good heat and hydrolytic stability

and vapor barrier properties [203].

41

New partially fluorinated monomer, 2,2-bis[4-(4-aminophenoxy)phenyl]

hexafluoropropane (BDAF) was synthesized at TRW, Inc. USA under a grant from

NASA –Lewis Research Center, and thermoplastic all fluoro-polyetherimide based on

6FDA and BDAF was reported in 1978 by Jones and coworker [142-144] and later by

Scola and coworkers at United Technologies and NASA Lewis Research Center [15,

204-205]. The technology was licensed by Ethyl Corp and the polyimide product was

commercialized under the trade name Eymide for high performance aerospace

applications. However, it was not cost effective for the performance it provided, just like

Hoechst Celanese’s SIXEF series of fluoro-polyimides. Although SIXEFproducts

performed better in a price-to-performance comparison study [3-5, 9, 15-16, 206].

For the synthesis of hexafluoroisopropylidene group containing monomers, e.g.

dianhydride and diamine, the literature search [30, 206-207] revealed that basic fluorine

chemistry coupled with extensive organic synthesis steps was involved. 2,2-Bis(3,4-

dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2,2-bis(4-amino phenyl)

hexafluoropropane (4,4-6F-Diamine), and 2,2-bis(3-amino phenyl) hexafluoropropane

i.e. (3,3-6F-Diamine), are all made from the starting material hexafluoroacetone (HFA).

In the 6FDA synthesis, o-xylene is reacted in the presence of hydrofluoric acid [HF] to

make an intermediate compound: 2,2-bis (3,4-dimethylphenyl) hexafluoropropane (DX-

F6), which on controlled air oxidation and subsequent dehydration leads to high purity

6FDA with very good yield (>90%). Similarly, in the case of 4,4-6F-Diamine, HFA is

reacted with toluene to obtain an intermediate compound, 2,2-bis(4-methylphenyl)

hexafluoropropane, which on air oxidation gives a dicarboxylic acid containing

compound: 2,2-bis(4-carboxyphenyl) hexafluoropropane (6FDCA). On amidation it

gives bisamide, 2,2-bis(4-aminocarboxyphenyl) hexafluoropropane, which upon

Hoffman rearrangement and hydrolysis, gives a high purity 4,4-6F-diamine. If 6FDCA

42

was nitrated using HNO3 in the presence of fuming sulfuric acid, it selectively would

give 2,2-bis(3-nitro, 4-carboxyphenyl) hexafluoropropane, which on decarboxylation

would give 2,2-bis(3-nitrophenyl) hexafluoropropane. However, the reaction was

sluggish and the final compound needed extensive purification before reduced to

diamine, 2,2-bis(3-amino phenyl) hexafluoropropane i.e. (3,3-6F-Diamine). Both these

diamines, because of their not so optimal yields, and need for time-consuming extensive

and costly purification steps, were prohibitively expensive. The chemical reaction

schemes for these monomers are shown in Figures 16 & 17.

Figure-16: Basic 6F-chemistry: 6FDA and diamine synthesis routes

Figure-17: Basic 6F-chemistry: 6F-Diamine synthesis route.

CH3

CH3H3C

H3CCH3

CH3

CH3

CH3H3C

H3C

CH3

CH3H3C

H3C CC

C

C

CF3

O O

O

OCO

CF3

O

NH2H2N

CH3

CH3H3C

H3C

NO2O2N

C O

F3C

F3C+

[HF]

- H2O2

1. Air Oxidation

2. (Ac2O); - 2H2O

Nitration, 80 oCconc. HNO3/H2SO4

Hydrogenation, [H]

20% Pd on C/THF 50 oC

HFA o-Xylene

6FDA

DX-F6

2,2 [bis (3-amino-4,5-dimethyl) phenyl] hexafluoropropane2,2 [bis (3-nitro-4,5-dimethyl) phenyl] hexafluoropropane

CCF3

CF3

CCF3

CF3

CCF3

CF3CCF3

CF3

2,2-bis(3,4 dicarboxyphenyl) hexafluoropropane dianhydride

2,2-bis(3,4 dimethylphenyl) hexafluoropropane [DX-F6]

CF3

NH2NH2CF3

CH3H3CCH3

C O

F3C

F3CCCF3

COOHHOOC CCF3

CONH2H2NOC CCF3

NH2H2N

CF3

NO2O2N

COOHHOOC C

CF3

O2N NO2CF3

C

CF3

C

+[HF]

- H2O2

HFA

CF3

Toluene

CF3Air Oxidation

CF3

CF3

CCF3

Catalyst

Amidation

[4,4-6F Diamine]4,4-6F Dibenzamide HNO3 / H2SO4

Nitration, 80 oC

Decarboxylation

-CO2

Hydrogenation

20% Pd/Cin THF

[3,3-6F Diamine]

4,4-6F Di acid

2,2- Bis (4-aminophenyl) hexafluoropropane

2,2- Bis (3-aminophenyl) hexafluoropropane 2,2 Bis (3-nitro-4 carboxyphenyl) hexafluoropropane

NH3/SO3H2

[-H2SO4]Hofmann Rearrangement

Hydrolysis

2,2 Bis(3-nitrophenyl) hexafluoropropane

2,2- Bis (4-methylphenyl) hexafluoropropane

43

Vora and coworkers have developed and reported a simplified one-pot, two-step

solution polymerization process for a commercial manufacturing of SIXEF-PI, i.e.

various fluoro-polyimides and copolyimides based on aromatic dianhydrides (Table 12)

and diamines containing bis-trifluoromethyl groups, and in combination of other non-

fluorinated monomers by polycondensation reactions [25-38, 101-112, 115, 118-119,

121-124, 127, 133-134, 139, 208-215]. The fluorinated monomers are very expensive,

especially diamines, as mentioned in the monomers sub-section of Section 1.3.1.

The most common procedure in lab synthesis is a simplified one-pot, two-step

polymerization synthesis process with due consideration given to major factors affecting

the condensation polymerization reaction as shown in reaction scheme in Figure 18.

Table-11: Effect of some factors on inherent viscosity and hence the molecular weights of poly(amic acid) [11, 139, 167, 182].*

Factor Effect Optimal choice Monomers quality Purity of monomer negatively affects

the reaction propagation kinetics, lower inherent viscosity typically means molecular weight built-up and hence the quality of Poly(amic acid)

Highest purity monomers (>99.8 %) with impurities at level not more than few ppm. Pre-dried monomer just before polymerization is highly preferred.

Reaction temperature

>25 oC, MW decreases, Between 15-20 oC, MW maximum At <10 oC, MW decreases

For higher viscosity, reaction temperature must be controlled in the range of 15-20 oC

Reaction time

Within the first 10 hr. Inherent viscosity and hence the MW increases with increasing time. After 10 hr. the viscosity is somewhat stabilized and MW of poly(amic acid) decreases slightly. Prolonged reaction time reduces MW drastically

Polymerization reaction time should not be longer than 15 hours; optimal time at 18 oC is 8-12 hr.

Molar ratio of two monomers

(Dianhydride/Diamine)

An excess of 1% molar ratio of monomers can reduce MW by 16-20%

1:1

Concentration of reactants

MW increases with concentration up to 25% solid, but too high concentration of monomers decreases properties of final polyimide product

15-20 %

Solvent Dipolar, aprotic solvent dissolves monomers readily. Dry solvent with very low moisture level preferred.

Dry NMP, DMAc, BLO, DMF, or mixture thereof with low moisture content (< 0.5%)

*: Synthesis of [6FDA + 4, 4’ -6F Diamine] poly(amic acid) was done in NMP solvent

44

A laboratory scale synthesis reactor set-up is shown in Figure-19. For example, in the

case of SIXEF-44 Polyimide based on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane

dianhydride (6FDA) and 2,2-bis(4-amino phenyl) hexafluoropropane (4,4-6F-Diamine),

accurately weighed equimolar amount of high purity, electronic grade 6FDA was added

to pre-dissolved diamine solution in freshly distilled NMP to make 15-30% non-volatile

(NV) solid concentration solution. Then this reaction mixture was stirred under an inert

atmosphere at carefully selected temperature for 5 to 20 hours to obtain high viscosity

poly(amic acid) (6F-44 PAA). A small sample of PAA was always retained for viscosity

measurement. The rest of PAA was then imidized to form polyimide (6F-44 PI) by in-

situ chemical imidization route.

Table-12: Monomers for fluoro-polyimides [215]

DIANHYDRIDE MONOMERS

PMDA C

C C

CO O

O

O

O

O

BPDA C

C C

C

O

O

O

O

O

O

BTDA C

C C

CC

O

O

O

O

O

O

O

ODPA C

C C

CO

O

O

O

O

O

O

6FDA C

C C

C

O

O

O

C

CF3

CF3

O

O

O

DIAMINE MONOMERS

3,3’-6F Diamine

C

CF3

CF3

NH2H2N

4,4’-6F-Diamine

H2N C

CF3

CF3

NH2

The chemical imidization was carried out by the addition of a predetermined mole ratio

of β-picoline (catalyst and acid acceptor) base and acetic anhydride (dehydrating agent)

and PA was successfully converted to PI. Solid polymer was obtained by precipitation in

methanol and de-ionized water and subsequent air drying for 24 hours and further drying

at 100°C overnight in an air-circulating oven [11, 38, 127, 139, 208-214].

45

Table-13: Fluoro-polyimide compositions and identification code [215]

FLUORO-POLYIMIDES BASED ON 3,3-6F-Diamine

FLUORO-POLYIMIDES BASED ON 4,4-6F-Diamine

PI CODE Dianhydride PI CODE Dianhydride Polyimides

[SIXEF-33] 6FDA [SIXEF-44] 6FDA [SIXEF-2033] BPDA [SIXEF-2044] BPDA [SIXEF-3033] BTDA [SIXEF-3044] BTDA

[ODPA-33] ODPA [ODPA-44] ODPA Co-Polyimides

6FC1M PMDA + 6FDA 6FC1P PMDA + 6FDA 6FC2M PMDA + BPDA 6FC2P PMDA + BPDA 6FC3M PMDA + BTDA 6FC3P PMDA + BTDA 6FC4M PMDA + ODPA 6FC4P PMDA + ODPA

Using the above procedure several new 6F-PI compositions (Table 13) were synthesized

and characterized [214].

C C

C

CCF3

O O

O

NNCO

C

C C

C

CCF3

O O

O

NNCO

C

n

n

CF3

CF3

C C

C

C

CF3

O O

O

OC

O

O

CF3

[ 6FDA + 4,4-6F Diamine ] Fluoro-polyimide (SIXEF-44)

CF3

CF3

CF3

CF3

C C

C

CCF3

O O

O

NNCO

C

CF3CF3

CF3


n


C C

C

C

CF3

O O

O

NNCO

C

n

CF3 CF3

CF3

CCF3

CF3NH2

Fluoro-polyimide (SIXEF-PI)

H2N

C C

C

C

CF3

O O

OCO

CF3

15-30% NV solidNMP at RTPOLYMERIZATION

6F-Diamine6FDASTEP 1

CCF3

CF3

HN

HO OH

+

HN

n

[6F-Poly(amic acid)] solution in NMP

STEP 2 Base (catalyst) / Acetic anhyydrideRT, 5 to 20 hours reaction time-2H2O

CHEMICAL IMIDIZATION

Figure -18: Synthesis scheme of SIXEF-PI and structures of three SIXEF fluoro-polyimides [214]

46

Fluoro-polyimides were then tested to determine their solution and intrinsic properties.

Their molecular weights were determined by gel permeation chromatography (GPC).

The polymers were cast into clear colorless films by solution casting method. These film

samples were characterized for their solubility, moisture uptake, thermal, thermal

stability, mechanical, electrical, etc. properties. Figure 20 shows a typical GPC curve for

the sample of SIXEF-33 and SIXEF 44 polyimides solids. These fluoro-polyimides

were of high molecular weights as well as high inherent viscosity. The various properties

of fluoro-polyimides and copolyimides are discussed in the characterization section

Figure-19: A typical laboratory synthesis reactor set up schematic for the fluoro-polyimides. [214, 218] While working at American Hoechst Corp., Vora [25-29, 214-215] invented new fluoro-

polyimides and copolyimide compositions and developed their manufacturing processes,

and produced them in large quantities. Hoechst Celanese Corp. (HCC) commercialized

these fluoro-polyimides under the brand name SIXEF for aerospace and electronic

applications. The manufacturing process plant schematic is given in Figure 21 [214-215]. Vora also synthesized fluoro-polyimides having 12F containing linking groups from

proprietary dianhydride and diamines [34, 115, 214-215].

Schematics of Laboratory Scale Synthesis of Fluoro-polyimides Schematics of Laboratory Scale Synthesis of Fluoro-polyimides

47

Figure-20: Molecular weight determination of sample of SIXEF-33 and SIXEF 44 polyimides solids by gel permeation chromatography (GPC) [208, 214]. .

Figure-21: SIXEF-PI manufacturing process plant schematic [213-215] Due to their excellent gas transport properties and high selectivity for the separation of

oxygen over nitrogen and carbon dioxide from air, fluoro polyimides are widely

investigated for the commercial development of gas separation membranes. Later at

SIXEF Polyimide Manufacturing Plant Schematics SIXEF Polyimide Manufacturing Plant Schematics

48

HCC, Vora modified laboratory synthesis techniques to manufacture special in-situ

formulation (dope) of fully imidized [6FDA+ Durene Diamine] fluoro-polyimide under

the brand name of SIXEF-Durene for the spinning of hollow fibers, which were used in

the development of gas separation membrane application by Chung et al [133, 140].

Chen and Vora later developed several fluoro-poly(amide imide) polymers having

superior thermal properties than commercially available Torlon brand of poly(amide

imide) products from Amoco Corp. USA for molded engineering parts applications [108,

128, 131, 135-137].

1.1.5. Characterization techniques for polyimides

1.1.5.1. Characterization of polyimide’s chemical characteristics [14, 16, 51, 151-

152, 177, 216-226]

During the preparation of polyimides and monitoring of reaction mechanism, FTIR,

and NMR spectroscopies are useful techniques for determining the chemical species in

the reaction systems and for understanding reaction processes. XPS is also used for

surface analysis and structural characterization of polyimides.

In comparison to the FTIR, the NMR determination requires the sample to be in a

solution, and only a few solvents can dissolve polyimides. The solvent as an impurity in

the sample also interferes with the analysis of NMR spectra. These limit the use of NMR

in the characterization of polyimides. Although solid-state NMR can be used, the

instrument is expensive and poses difficulty regarding resolution of the peaks.

1.1.5.2. Characterization for polyimide’s physical characteristics

Characterization of the physical properties of polyimides is very important. TGA,

DSC, TMA DAM, DEA, GPC, viscometry, XRD, mechanical testing, etc. are very

useful techniques. Table 14 lists the capabilities of these techniques in the

characterization of polyimides.

49

Table-14: Instruments for characterization of physical properties of polyimides

Instrument Determination

TGA Thermal stability, decomposition temperature, degradation mechanism

DSC Tg, mp, and degradation mechanism, LCP.

TMA Tg, mp. CTE

Tensile testing machine Tensile strength, elongation, modulus

Dielectric analysis Dielectric constant, dielectric strength, dissipation factor, resistivity

X-ray diffraction Crystallinity of polyimides

GPC Molecular weight

Viscometry Viscosity and molecular weight for polyimides

1.1.5.2.1. Glass transition

Polymer scientists pay close attention to the relationship between the chain structure

and the glass transition temperature and find proper approaches to lower the Tg, thus

making the polyimides more tractable and processable without sacrificing their other

outstanding properties [2, 14, 16, 51].

Figure-22: Tg transition of PEI (ULTEM1000) measured by: (a) DSC, and (b) TMA [223]. The Tg transitions can be measured by DSC, TMA, and DMA. The most convenient

way is DSC. Figure-22 (a) shows the DSC thermograph of polyetherimide (ULTEM

1000) at a heating rate of 20°C/min. The Tg transition is at about 218°C. However, in

some cases, the Tg transition is not so clear in DSC curves, making the accurate

150 170 190 210 230 250 270 290

<< E

ndo

(a)

Temperature °C50 70 90 110 130 150 170 190 210 230 250

-1000

0

1000

2000

3000

4000

Tg

(b)(b)

Temperature °C

Dim

ensi

on C

hang

e µm

150 170 190 210 230 250 270 290

<< E

ndo

(a)

Temperature °C150 170 190 210 230 250 270 290

<< E

ndo

(a)

Temperature °C50 70 90 110 130 150 170 190 210 230 250

-1000

0

1000

2000

3000

4000

Tg

(b)(b)

Temperature °C

Dim

ensi

on C

hang

e µm

50 70 90 110 130 150 170 190 210 230 250-1000

0

1000

2000

3000

4000

Tg

(b)(b)

Temperature °C

Dim

ensi

on C

hang

e µm

50

determination difficult. Tg transition can also be clearly determined from the dimensional

change of this polymer by thermo-mechanical analysis (TMA) as shown in Figure-22 (b)

[223].

The Tg is the temperature above which segments in the polymer chains have sufficient

rotational energy to overcome the forces that restrict the torsional oscillations and hinder

their transition to free rotation [2]. Generally, the Tg is a measure of chain rigidity.

Therefore, most work on lowering the Tg was concentrated on reducing the rigidity of

polyimide chains, for example by introducing flexible linkage such as oxygen, sulfone,

perfluoroalkylene segments in either dianhydride or diamine moieties. However, there

are many other factors that may affect the Tg of polyimides, for instance: molecular

weight, nature of end groups, extent and method of imidization, moisture uptake and

residual of solvent.

°°

Figure-23: Tg of select few fluoro-polyimides from Hoechst Celanese Corp, determined by DSC [225] Figure-23 shows the effect on the glass transition temperature of incorporating flexible

linkages in the dianhydride and structural changes in fluorinated diamines in several

fluoro-polyimides from Hoechst Celanese Corp. Tgs were determined by DSC [222,

226].

51

The literature has also indicated the influence of flexible linkages in the dianhydride or

diamine portion on Tg transition [14, 16, 227]. It seems that the insertion of flexible

linkage in the dianhydride has a greater impact on the lowering of Tg than that in the

diamine. This cannot be well explained by the chain rigidity but represents a difference

in intermolecular interactions.

Monomeric aromatic imides and anhydrides are strong electron acceptors, and form

charge transfer complexes (CTC) with electron donors such as amine groups [2, 14, 16,

227-229]. The strength of this interaction is determined by the electron affinity of the

dianhydrides and ionization potential of the diamines. As polyimide is generally

composed of alternating electron acceptor, dianhydride, and donor, diamine, they may

form very strong inter-molecular chain charge transfer complexes. This hypothesis was

proved by the absorption bands in the UV spectra of a series of polyimides similar to the

bands observed for CTC’s of monomeric imides [229]. The wavelength and intensity of

the bands were dependent on the electron affinities of the dianhydrides and ionization

potential of the diamines.

According to the above explanation, the great impact on Tg by changing the flexibility

of dianhydride can be easily understood. A “hinge” group, such as –O–, –CO–, –S–, –

SO2–, in the dianhydride will always decrease the strength of the CTC relative to

pyromellitide dianhydride (PMDA), irrespective of its electronic characteristics because

it reduces the electron affinity of the dianhydride by isolating the powerful electron

withdrawing anhydride group from each other. However, a “hinge” in the diamine can

either increase or decrease the strength of the CTC, depending on whether it is electron

donating or withdrawing. Long chain aliphatic or organic substituent groups attached to

the main chain may hinder the chain packing, thus reducing the glass transition

temperatures.

52

1.1.5.2.2. Glass transition in copolymers and miscible polymer blends

Miscible polymer blends or copolymers show a single Tg transition in the DSC curves.

The Tg of a copolymer or blend can be roughly predicted from the Fox equation [230]:

2

2

1

11

ggg TW

TW

T+=

(2) where Tg is the glass transition temperature of the copolymer or blend, W1 and W2 are

the weight fractions of the homopolymer or blend’s individual polymer components 1

and 2, Tg1 and Tg2 are their corresponding glass transition temperatures. [230]

Chung et al. [231-234] reported several pairs of miscible fluorine-containing

polyimides and copolymers which are shown in Table 15. Based on their experimental

results, they concluded that: if (1) the dianhydride composition was the same in each pair

and (2) the diamine was changed from the 3,3-(meta-substituted) 6F-diamine to the 4,4-

(para-substituted) 6F-diamine, the fluorine-containing polyimide pairs were miscible.

Table-15: The Tg (°C) of miscible fluorine-containing PI/PI blends [231-234]

DIANHYDRIDE MONOMERS

PMDA

O

O

O

O

O

O

BPDA

O

O

O

O

O

O BTDA

O

O

O

O

O

O

O

C

ODPA

O

O

OO

O

O

O

6FDA

O

O

OO

O

O

CF3

CF3

DIAMINE MONOMERS

3,3’-6F-diamine

NH2H2NCF3

CF3

4,4’-6F-diamine

CF3

CF3

H2N NH2

3,3’-6F-diamine 4,4’-6F-diamine Blend of polymers Polymer

Code Dianhydride Tg1

Polymer

Code Dianhydride Tg2 Ratio-(50:50) Tg

6F1M 6FDA 250.5 6F1P 6FDA 318.5 6F1M + 6F1P 275.0

6F2M BPDA 267.0 6F2P BPDA 343.0 6F2M + 6F2P 279.3

6F3M BTDA 239.0 6F3P BTDA 304.0 6F3M + 6F3P 252.8

6F4M OPDA 224.5 6F4P OPDA 305.0 6F4M + 6F4P 242.7

6FC1M PMDA + 6FDA 270.9 6FC1P PMDA + 6FDA 354.0 6FC1M + 6FC1P 295.0

6FC2M PMDA + BPDA 280.0 6FC2P PMDA + BTDA 375.0 6FC2M + 6FC2P 295.5

6FC3M PMDA + BTDA 261.0 6FC3P PMDA + BTDA 349.5 6FC3M + 6FC3P 273.4

6FC4M PMDA + OPDA 233.0 6FC4P PMDA + OPDA 347.0 6FC4M + 6FC4P 258.4

53

1.1.6. Processes and properties Changes in the world economy and reduction in abundance of natural resources have

contributed to the increased use of high-performance engineering thermoplastic and

thermoset materials [2-5, 9-10, 16, 20, 235- 241]. Currently, polyimides containing both

aromatic and heterocyclic structures in the main-chain are one of the best high-

performance engineering plastics. Polyimides have many unique properties among which

are outstanding stability toward thermal, oxidation and irradiation; excellent mechanical

properties, good electrical properties and low CTE (coefficient of thermal expansion) as

well as dimension stability. Thus, polyimides have found uses as high-temperature stable

materials in adhesives, dielectric coatings, photoresists, aerospace composites,

electronics, optoelectronics, fiber optics, for membrane separation etc. applications,.

1.1.6.1. Processing of polyimides

Processing of polyimides is not an easy task because of the characteristic high Tg, and

high or no melting point. Besides, many polyimides are insoluble and infusible, and

cannot be processed by conventional polymer processing equipment [2-5, 9-10, 16, 20].

The processing difficulty may be the main reason why only a few polyimides have

been successfully commercialized [2-5, 9-10, 16, 20, 177, 184]. Therefore, it is most

desirable to synthesize new polyimides with conventional thermoplastic characteristics

but with high performance regarding thermal, mechanical and electric properties. The

current processing methods producing commercial polyimides are reported in Table 16.

There are ways polyimides such as polyetherimide and polyimide-silicones can be

successfully processed. Since these polyimides have lower Tg and melting points owing

to the more flexible ether bond and Si-O bond (easy rotation) existing in polyimide

main-chains, they can be processed on conventional molding process equipment. It has

been reported in literature that some polyetherimides possess Tm as high as 400 oC and

54

Tg of 260 oC [2, 10, 14-15, 52-53, 204, 226]. Obviously, in processing these types of

polyetherimides, one has to strike a balance between the minimum thermal processing

temperatures to be used and avoid polymer’s thermal degradation temperatures.

Table-16: Current processing methods for commercial polyimides [2-5, 9-10, 14, 16, 20, 177, 184]

Trade Name Physical Form Main Composition

(dianhydride + Diamine)

Processing Method Company

KaptonH PAA Solution [PMDA+4,4-ODA] Film Casting DuPont

Vespal PAA Powder [PMDA+4,4-ODA] Powder metallurgy DuPont PyralinML PAA solution [PMDA + MDA] Thin film enamel DuPont NR-150 Solution [6FDA+ m-PDA] Lamination DuPont ULTEM 1000 Pellet [BPADA + m-PDA] Molding GE Plastics

ULTEM 1010 Pellet Phthalic anhydride end

capped [BPADA + m-PDA]

Extrusion Molding GE Plastics

ULTEM 1000 Solution [BPADA + m-PDA] Fiber spinning GE Plastics

PMR-15 PAA Nadic anhydride end capped

oligomer of [PDA + MDA]

Lamination NASA

LARC-TPI PAA Solution BTDA + 3,3-DAB] Lamination NASA

Polyimide2080 Powder [BTDA+20%MDI +80%TDI] Molding Upjohn Co.

UPILEXR PAA Solution [BPDA + 4,4-ODA] Film Casting Ube Industries

UPILEXS PAA Solution [BPDA + p-PDA] Film Casting Ube Industries

Thermid7000 Solid Acetylene terminated

oligomer of [6FDA+APB]

Molding National Starch

SIXEF-33 Solid [6FDA + 3,3-6F-Diamine] Compression molding Hoechst Celanese

SIXEF-44 Solid [6FDA + 4,4-6F-Diamine] Compression molding

Solution Casting

Hoechst Celanese

SIXEF-Durene Formulation [6FDA+1,4-Durene Diamine] Hollow Fiber spinning Hoechst Celanese

1.1.6.2. Mechanical, thermal, and thermal oxidation stability properties

1.1.6.2.2. Mechanical properties

Owing to the very rigid main-chain structure, aromatic polyimides possess very high

strength and modulus (Table 17). These unique properties render their uses as high

strength films and fibers, and lightweight high-performance composite parts for

aerospace and microelectronics. Table 18 gives a comparison of thermal and mechanical

properties of fluoro-polyimides and conventional polyimides [11, 40, 46, 208-215, 226].

55

Table-17: Typical mechanical properties of polyimides [14, 16]

POLYMER COMPOSITION

(Dianhydride + Diamine)

Tensile Strength @ Break (Kpsi))

Elongation at Break @ RT

(%)

Modulus

(GPa)

5% weight loss in air (K)

[PMDA + BPDia] 200 2 7.0 773

[PMDA + ODA] 160 40-100 3.5 743

[PMDA + BZPDia] 125 20 2.3 768

[PMDA + MDA] 120 65 2.9 793

1.1.6.2.3. Thermal properties

The service temperature and durability are essential for modern high performance

materials. The thermal stability of many aromatic polyimides can exceed 600 oC in

nitrogen and 500oC in air and can be used at high temperatures for a longer period of

time [160]. Their irradiation and cryogenic resistant properties render them to be

successfully used in aerospace and nuclear devices.

Figure-24: Thermal stability by TGA of fluoro-polyimides from Hoechst Celanese [238]. Recently, it has been reported that the long-period service temperature of some

polyimides approaches 371oC in air [2, 11, 14, 16, 177]. The outstanding thermal

stability of polyimide is associated with the very rigid main-chain backbone, which

contains both aromatic rings and heterocyclic structures (imide ring). Thermal stability

56

decreases, while processebility increases upon the incorporation of aliphatic or ether

chains in the main-chain backbone of polyimides.

Thermal stability as determined by TGA for fluoro-polyimides from Hoechst Celanese

is given in Figure 24 above and also reported in Table 18. [225].

Table-18: Thermal and mechanical properties of SIXEF-PI films (fluoro-polyimides and copolyimides) from Hoechst Celanese Corp. and compared with Kapton H (from Dupont) and ULTEM 1000 (from GE Plastics) films [11, 38, 40, 46, 208-215, 225]

POLYMER COMPOSITION

F.T

(µm)

DSC Tg (°C)

TGA 5%

Wt. Loss @

20°C/mi Air (°C)

TOS Wt. Loss

@ 343°C for 300 hr in

Air (%)

Elongation @

Break (%)

Stress @

Break (ksi)

Young’s Modulus

(ksi)

POLYIMIDES [6FDA + 3,3-6F DAM] 75.00 255 527 4.10 4 14 470 [6FDA + 4,4-6F DAM] 75.00 320 542 4.10 8 15 400 [6FDA + 3,4-6F DAM] 31.25 285 520 4.16 NA NA NA [PMDA + 4,4-6F DAM] 37.50 405 510 NA Brittle film [BPDA + 4,4-6F DAM] 75.00 355 540 6.14 22 18 390 [BTDA + 4,4-6F DAM] 50.00 307 535 6.37 10 15 380 [ODAP + 4,4-6F DAM] 75.00 311 536 4.82 10 14 294

COPOLYIMIDES

[Dianhydride Composition in 0.5:05 mole ratio]

[(BPDA + PMDA) + 4,4-6F DAM] 50.00 386 530 4.54 20 14 290 [(BTDA + PMDA) + 4,4-6F DAM 50.00 364 530 5.49 21 14 271

[(ODAP + PMDA) + 4,4-6F DAM] 75.75 350 525 4.73 12 13 252 [(ODPA + BPDA) + 4,4-6F DAM] 75.00 328 525 4.44 9 15 321 [(ODPA + BTDA) + 4,4-6F DAM] 57.50 310 540 5.14 8 13 297 [(ODPA + 6FDA) + 4,4-6F DAM] 82.50 311 562 4.30 9 13 270

[(6FDA + PMDA) + 4,4-6F DAM] 62.50 362 515 4.59.. 5 10 324

[6FDA + BTDA + 4,4-DDSO2] 50.00 333 530 NA 2 9 499

[6FDA + BTDA + 4,4-DDSO2+m-PDA] 50.00 321 540 NA 4 13 450

[PMDA + 6FDA + 4,4’-ODA+4,4-6FDAM] 31.25 367 538 NA NA NA NA

COMPARATIVE COMMERCIAL POLYIMIDE

Kapton-H 25.00 407* 605 22.0 72 25 430 ULTEM 1000 25.00 220 522 10.0 60 15.2 430

F.T: Film thickness, DSC: Differential Scanning Calorimetry, TGA: Thermogravimetric Analysis TOS: Thermo-oxidative stability; * measured by TMA: Thermo mechanical Analysis. It is very clear from Table 18, that the observed glass transition temperature (Tg)

varied, based on the dianhydride structure incorporated in the polymer. The trend of Tg

in the polyimide decreased in the following order:

57

PMDA > BPDA > 6FDA > BTDA > ODPA.

The thermal decomposition temperature (5% weight loss) ranges from 510 to 540°C

for SIXEF -PI, 522°C for ULTEM1000 and 605°C for KaptonH films.

1.1.6.2.4. Thermo-oxidative stability (TOS) of polyimides

Figures 25 to 27 as well as Table 18 illustrate a comparison of thermo-oxidative

stability (TOS) for conventional polyimides, fluoro-polyimides and Kapton H and their

chemical structures. Clearly, fluoro-polyimides out-performed conventional polyimides

[10-11, 38, 40, 208-215, 225].

Figure-25: Effect of dianhydride structures on the thermo-oxidative stability (TOS) of polyimides films (composition having different dianhydrides) isothermally heated at 316 °C (600°F) [10].

Figure-26 shows the thermo-oxidative stability (TOS) of Kapton and some fluoro-

polyimides, and copolyimides when isothermally heated at 315°C (~600°F) in air [38].

Whereas, Figure 27 shows the chemical structure and Thermo-oxidative stability (TOS)

of Hoechst Celanese Corp.’s fluoro-polyimide (SIXEF-44) [10] and DuPont’s

polyimide Kapton H at 343°C (~650°F) for 300 hours in air [11, 40, 208-215, 225]

58

Figure-26: Thermo-oxidative stability (TOS) of some fluoro-polyimides and copolyimides when isothermally heated at 315°C (~600°F) in air [38]

Figure-27: The chemical structure and thermo-oxidative stability (TOS) of fluoro-polyimide (SIXEF-44) [10] and Kapton H at 343°C (~650°F) for 300 hours in air [11, 40, 208-215, 225] 1.1.6.3. Electrical and optical properties, dimensional stability and coefficient of

thermal expansion (CTE) 1.1.6.3.1. Electrical properties

Most polyimides inherently have low (< 4.5) dielectric constant (ε’). The search for

new polyimides having lower dielectric constant, good electrical properties, higher

continuous-use temperature with good hydrolytic stability and ease of processability are

the constant focus of research both in academia and in industry [2, 14-16].

Tables 19 lists the electrical properties of commercial polyimides, DuPont’s

KaptonH, GE Plastics’ ULTEM1000, and Hoechst Celanese’s SIXEF-PIs fluoro–

polyimides and fluoro-copolyimides.

0

5

10

15

20

25

0 24 72 140 200 300

Aging Time at 343oC [650oF] (hours)

Wei

ght L

oss

(%)

SIXEF-44 ( 50 micron thickness)

Kapton H ( 50 micron thickness)C C

C

C

CF3

O CF3 O

O

N

CF3 n

[6FDA + 4,4-6F Diamnie] Fluoro-polyimide (SIXEFTM-44) Film

C

C

C

O O

O

N

C n

[PMDA + ODA] Polyimide (KAPTONR H) Film

C

CF3

C

O

N

O

N O0

5

10

15

20

25

0 24 72 140 200 300

Aging Time at 343oC [650oF] (hours)

Wei

ght L

oss

(%)

SIXEF-44 ( 50 micron thickness)

Kapton H ( 50 micron thickness)C C

C

C

CF3

O CF3 O

O

N

CF3 n

[6FDA + 4,4-6F Diamnie] Fluoro-polyimide (SIXEFTM-44) Film

C

C

C

O O

O

N

C n

[PMDA + ODA] Polyimide (KAPTONR H) Film

C

CF3

C

O

N

O

N O

59

KaptonH and ULTEM1000 films have dielectric constants (ε’). of 3.5 and 3.15

respectively, whereas for SIXEF-PI, the dielectric constant value is 2.58.

Table-19: Electrical properties of SIXEF-PI films (polyimides and copolyimides based on fluoro-diamines and non-fluoro diamines) from Hoechst Celanese Corp. and compared with Kapton H and ULTEM 1000 films [11, 38, 40, 46, 208-215, 225,241]

POLYMER

COMPOSITION

Film Thickness

(µm)

Dielectric Constant

ε’ @ 10 MHz

Dielectric Strength

(Volt/25µm)

Dissipation Factor

@ 10 MHz

Volume Resistivity

(Ohm-cm)

Surface Resistivity

(Ohm)

POLYIMIDES [6FDA + 3,3-6F Diamine] 75.00 2.55 1933 1.5 x 10-3 1.97 x 1016 3.14 x 1014 [6FDA + 4,4-6F Diamine] 75.00 2.58 1500 1.8 x 10-3 1.92 x 1016 3.14 x 1014 [6FDA + 3,4-6F Diamine] 31.25 2.59 3280 4.3 x 10-3 [BPDA + 4,4-6F Diamine] 75.00 2.56 1900 1.7 x 10-3 2.12 x 1016 2.99 x 1014 [BTDA + 4,4-6F Diamine] 50.00 3.17 3110 1.6 x 10-3 2.93 x 1016 [ODAP + 4,4-6F Diamine] 75.00 2.36 1660 3.1 x 10-3 1.46 x 1016

COPOLYIMIDES with 4,4-6F Diamines

[Dianhydride composition in 0.5:05 mole ratio]

(6FDA + PMDA) 62.50 2.40 1960 1.7 x 10-3 2.12 x 1016 2.99 x 1014 (BPDA + PMDA) 50.00 2.33 2000 1.6 x 10-3 2.93 x 1016 3.26 x 1014 (BTDA + PMDA) 50.00 2.40 2300 2.2 x 10-3 2.76 x 1016 3.14 x 1014

(ODAP + PMDA) 82.50 2.72 1660 3.1 x 10-3 1.46 x 1016 (ODPA + BPDA) 75.00 2.54 1410 2.0 x 10-3 1.17 x 1016 (ODPA + BTDA) 57.50 2.52 1640 2.8 x 10-3 2.05 x 1016 (ODPA + 6FDA) 82.50 2.46 1290 1.8 x 10-3 1.30 x 1016

[(6FDA + BTDA)

+ 4,4 DDSO2]

50.00 2.56 2050 2.7 x 10-3

[(PMDA + 6FDA)

+ (ODA + 4,4-6F Diamine)]

31.25 2.44 4080 3.9 x 10-3

COMPARATIVE COMMERCIAL POLYIMIDES

Kapton-H 25.00 3.20 3900 1.6 x 10-3 1.66 x 1016 3.22 x 1014 ULTEM 1000 25.00 3.15 710 1.3 x 10-3 6.7 x 1017

Table 19 also illustrates that polyimide polymers possess very good electrical

properties and fluoro-polyimides have the lowest dielectric constants for use as superior

insulators and for IC packaging. [11, 38, 40, 46, 151-152, 208-215, 225]

60

1.1.6.4. Optical properties

Polyimides can be looked at as polymeric chains with alternating electron donor and

acceptor elements which can interact with each other to form interchain charge transfer

complexes (CTC) [2, 10, 14, 16, 193-198, 227, 243].

Most conventional polyimides have dark amber to brown coloration due to the above

charge transfer complex phenomenon which, in turn, is associated with the electronic

characteristic of the monomer used in the synthesis. Koton et al. [14] explained that the

transparency of visible light by many non-fluorinated polyimides films decreased as film

thickness increased and known to have yellow to dark amber colors whereas fluorinated

polyimides films are almost colorless. Also optical transparency to visible light is

affected by the intra- and inter-molecular interactions of π electrons between the

monomer moieties in the polymer chain inducing a charge transfer complex (CTC). The

π electron transfers from the electron donating diamine to the electron accepting

dianhydride moiety.

Polyimides made with PMDA have higher strength of CTC. The anhydride groups are

closer to each other, thus providing a greater interchain interference with free rotation,

making closer chain packing and stronger CTC. These polyimides have darker color.

However, when a flexibilizing group is introduced between these anhydride groups, the

increase in the distance between them would reduce the CTC. These polyimides have

lighter coloration. However, the flexibilizing group of diamine can either increase or

decrease the CTC, depending on whether it is electron donating or withdrawing. But

most certainly, a flexibilizing group in dianhydride, on the other hand, will always

reduce the CTC relative to PMDA, irrespective of its electronic characteristics, because it

reduces the electron affinity of the dianhydride by isolating the powerful electron

withdrawing anhydride groups from each other. [2, 14, 16, 198, 226]

61

It is possible to reduce the CTC further by incorporating highly electronegative

fluorine groups or incorporating bulky electron withdrawing substituent groups on the

polymer backbone, as they restrict the inter-chain conformational mobility and thus

lower the CTC. Such polyimide films will have lighter coloration to totally colorless.

[13, 15, 198, 226-227]

Figure-28: UV-Visible spectra of 12.5 µm fluorinated and conventional polyimide films [193-198]

The fluoro-polyimides made from 6FDA are known for their excellent transparency in

the range of 80 to 90 % at 500 nm solar wavelength as compared to 72 and 27 % for light

amber to amber colored ULTEM 1000, and KaptonH films as shown in Figure 28 [16,

193-199, 243].

1.1.6.5. Dimensional stability and CTE

The dimensional stability and CTE matching with the wafer or metal for IC packages

are very important in the microelectronics industry. Unfortunately, many polymers

possess unacceptable shrinkage during the curing or cooling process, and consequently

have high CTE. A large shrinkage may induce extra stress within the multi-layer

coatings on a substrate (in a molded part or device). It may then cause local cracking or

Wavelength (nm)

Tran

smis

sion

(%)

Wavelength (nm)

Tran

smis

sion

(%)

62

delamination among the layers or between the multi-layer and the substrate. Mismatch of

polyimide CTE with the wafer or metal also causes stress, and possible delamination,

thus reducing the product quality. Therefore, polymers used for electronics packaging

must possess dimensional stability and a well-matched CTE with the wafer and metals

(e.g. Cu, Al) [298]. Tables 20 illustrate the CTE, mechanical properties and moisture

uptake of some polymers and metals or inorganic materials. Generally, the CTE of wafer

is low, only a handful of polymers meet such low CTE for such packaging application,

and polyimide is one of them.

Table-20: CTE of some electronic materials [2, 14, 16, 151-152]

Materials

Silicon

(Wafer)

Cu Al Al2O3 Glass PMDA-ODA BPDA-PDI PI(3FCDA-PPD)

CTE,

(ppm/K)

2.3-2.8 17 23 6.3-6.7 1-3 30-40 0.5-40 3.0

1.1.6.6. Other properties

Table 21 summarizes the intrinsic viscosity, solubility and moisture uptake properties

of fluoro- polyimides, copolyimides based on various fluorinated diamines and aromatic

dianhydrides, ULTEM 1000 and KaptonH in various solvents, such as NMP, DMF.

THF, DMAc, BLO, etc.

Some of these fluoro-polymers have high inherent viscosities and high molecular

weights. They have improved solubility in the organic solvents tested due to the fact that

the polymer chain backbone contained the perfluoroisopropylidene groups e.g.

1,1,1,3,3,3-hexafluoroisopropyl (HFIP), in their dianhydride and diamine structures as

compared to non-fluorinated polyimides. The observed solubility was in the following

order: Non-fluorinated > Partially fluorinated > Fully fluorinated polyimides.

The knowledge of moisture up-take properties of polyimide materials is important

with regards to their practical use in aerospace composites applications, encapsulation

63

application in microelectronics, and separation membranes applications. The absorbed

water in polyimide structure affects their performance and long term stability and

reliability. It is noted here that fully fluoro-polyimides have very significantly lower

moisture uptakes at 100 RH at 50°C as compared to partially fluorinated and

conventional non-fluorinated polyimides ULTEM 1000 and KaptonH (Table 21). This

is due to the fact that most fluoro-polyimides have hydrophobic –C(CF3)2– groups either

in the dianhydride or in the diamine or in both dianhydride and diamine structures [11,

38, 40, 46, 208-215, 225].

Table -21: Viscosity, molecular weights, solubility and moisture uptake properties of fluoro-polyimides

Inherent Viscosity

(dL/g) @ 25°C in NMP

Molecular weights by GPC 1 (Polystyrene standard)

POLYMER COMPOSITION

PA PI Mw Mn PD

Solubility2

Moisture uptake3

(%)

[6FDA + 3,3-6F DAM] 0.73 0.53 131,000 52,100 2.5 Sol 1.10 [6FDA + 4,4-6F DAM] 1.14 1.00 243,000 135.000 1.8 Sol 1.10 [6FDA + 3,4-6F DAM] 0.42 0.31 42,000 18,900 2.2 Sol 1.10 [PMDA + 4,4-6F DAM] 0.50 Ins NA NA NA Ins NA [BPDA+ 4,4-6F DAM] 1.07 0.97 140,000 80,000 1.7 Sol NA [BTDA + 4,4-6F DAM] 1.15 0.73 95,000 32,700 1.7 Sol NA [ODDA + 4,4-6F DAM] 1.35 1.10 117,000 47,000 2.4 Sol

[ODDA + PMDA + 4,4-6F DAM] 0.81 0.70 113,900 39,300 2.9 .Sol NA [ODDA + BPDA + 4,4-6F DAM] 1.03 0.95 159,000 67,500 2.4. .Sol NA [ODDA + BTDA + 4,4-6F DAM] 0.99 0.82 149,200 78,200 1.9 Sol NA [ODDA + 6FDA + 4,4-6F DAM] 0.92 0.80 129,400 50,100 2.6 Sol NA

[6FDA+BTDA + 4,4-DDSO2] 0.78 0.50 42,500 14,600 3.0 Sol 2.95 [6FDA+BTDA + 4,4-DDSO2+ m-PDA] 0.50 0.43 39,800 18,000 2.5 Sol 3.05

[PMDA + 4,4-ODA] 1.50 Ins NA NA NA Ins 3.15 [PMDA+6FDA+4,4’-ODA+4,4 6FDAM] 0.96 0.69 47,300 24,900 1.9 Sol 1.2

ULTEM 1000 NA 0.78 121,000 48,400 2.5 Sol 1.52 KaptonH * NA Ins NA NA NA Ins 3.0

1 : Using Polystyrene standard 2 : Organic solvents – NMP, THF, DMAc, DMF, BLO, DMSO and dilute sulfuric acid between 20-50°C 3 : Moisture up-take measured on polymer Films at 100% RH at 50°C for 100 hr * : As received film sample

1.1.7. Applications of polyimides

In order to achieve higher reliability and better quality of electronic and other high

value-added products, it is necessary that the polymers used in these applications possess

good dielectric properties, outstanding thermal stability, high strength, low CTE and

64

good adhesion to metals (e.g., Cu, Al), wafer and substrate. Polyimides typically possess

most of the above properties in addition to good planarity with less pin-hole density. As

a result, polyimides are especially suitable for applications in electronics and

microelectronics. The main applications of polyimides in this area are as follows:

1.1.7.1. Films

The first commercial polyimide was Kapton film, which was developed by DuPont

using the casting method in 1960 [2-4, 14, 16, 20, 151-152]. Since then, the applications

of the Kapton film, because of its outstanding thermal stability, and mechanical and

reasonable dielectric properties has been rapidly extended into the aerospace, defense

and electronics industry.

The main applications of polyimide films are as electrical insulators in military

hardware, aerospace, wire, cable and as insulator slot in electric motors and generators

[2-7, 9, 14-16, 20, 235-241]. The benefits of using polyimide films for insulation slot are

multiple. It permits better packing with a lighter weight and a 1.5-2.0-fold enhancement

in the efficiency of electric motor and improvement in their dissipation property because

of a 2-3-fold decrease in insulator thickness. In addition, the service temperature is

increased to 300oC for a longer period and at 480oC for a shorter period because of the

high strength and thermal stability of polyimide films. The non-flammable property of

polyimides makes the film insulators widely applicable in aerospace, airplanes,

automobiles, and in building industries. Recent research shows that the fluorine-

containing polyimides possess superior insulation properties, than the conventional

polyimides. And therefore have aroused a great deal of interest in both academics and

industry [2-7, 9, 14-16, 20, 160-164].

1.1.7.2. Molded plastics

It has been reported that DuPont’s Vespel brand of polyimide can be directly molded,

65

not by conventional molding processes, but by a process similar to a powder metallurgy

method [2, 14, 16, 20, 151-152]. In this case, it requires higher temperatures and special

equipment. Other thermoplastic polyimides, such as ULTEM (polyetherimide), and

LARC-TPI (thermoplastic polyimide) may be processed by conventional extrusion and

molding equipment. Polyimide is also a good matrix for carbon or glass fiber reinforced

composites which are widely used in aerospace applications. Thermosets polyimides,

e.g. PMR-15 series and those with photosensitive groups have been developed by

NASA are excellent successful examples [2-5, 14, 16, 20,151-152, 244-245]. These

materials not only possess good mechanical properties (toughness), but also have good

interfacial properties (surface energy and adhesion). Due to their outstanding thermal

stability, non-flammability and high strength, polyimide foams are suitable lightweight

materials for high temperature insulation applications, and for sound barriers in aircraft

and rocket construction [2-7, 9-10, 14, 16, 20, 245].

1.1.7.3. Fibers

The preparation and performance properties of polyimide fibers were first reported in

the 1960's by Dupont [2]. These fibers were derived from PMDA and aromatic diamines

ethylene bridge group[2-5, 14, 16, 20]. The synthesis process was involved two steps. In

the first step, the fibers are spun from a solution of polyamic acid by traditional “wet” or

“dry” spinning, which in the second step undergoes a thermal imidization at elevated

temperatures along with mechanical treatment to yield the final polyimide fibers. The

mechanicals and thermal properties of some heat resistant organic polymers are tabulated

in Table 22.

A few types of polyimide fibers are manufactured on a pilot plant scale in the USA

and Russia [2-5, 14, 16, 20, 146]. The main advantages of polyimide fibers are their high

thermal stability and strength, good electronic properties, non-flammability and radiation

66

resistance.

Table-22: Properties of some heat resistant organic fibers [2-5, 14].

Fiber Thermal

stability

(K)

Tensile

strength

(kPsi)

Tensile

elongation

(%)

Modulus

(GPa)

573 K*

(250 hr)

673 K*

(100 hr)

773 K*

(10 hr)

Aromatic polyamide 633 350 3-20 150 60 40 10

Polyarylimides 673 200 8-10 130 60 45 30

Ladder polymers >673 40 3-5 50 95 70 50

*: The strength retention of fiber at different temperature for given time, in %.

It can be used in the temperature range between 275 to 500oC. All these characteristics

indicate that polyimide fibers belong to a class of high performance fibers. They are

primarily being used in the weaving of high temperature insulating and non-combustible

fabrics for fire fighters and astronaut’s space suits. However, owing to the problems of

high cost, toxicity of monomers and processing difficulty, polyimide fiber is difficult to

compete with other high temperature organic fibers such as Kevlar (Dupont) which can

be used to a temperature up to 300 oC, without losing their superior strength and

modulus.

1.1.7.4. Adhesives and Varnishes

Polyimide varnishes have been used as binders for glass, plastics and laminates,

thermally stable adhesive compositions, and as high temperature coating materials [2-7,

9-10, 14, 16, 20, 48, 245-246]. In 1961, DuPont introduced varnishes under the trade

name Pyre-Ml whose composition is 14-17.5 % polyimide obtained from PMDA and

aromatic diamines [2,16]. Other high temperature thermoplastic polyimide adhesives are

LARC-TPIs [10], developed by NASA, and have been widely used for aerospace

applications.

1.1.7.5. Printed circuit board and packaging materials

In microelectronics, polyimides are used as the substrate for the printed circuit board,

67

photosensitive dielectric insulation layer, packaging encapsulant materials. The major

competitor of polyimides is epoxy. Approximately 50-60% of the electronics

applications use epoxy resins. Nearly 70% of the printed circuit boards manufactured are

made from epoxy resin. This is due to the fact that epoxy resins are cheap and easy to

process. However, IC boards made from epoxy resin can be used at maximum

temperature in the range between.120-150oC only. Therefore, polyimides with good

thermal stability are more suitably used such application. The flexible printed circuit

boards made of polyimides are functional up to 300oC without loosing it flexible

characteristics. Beside that polyimides have been widely used in microelectronics as

essential materials for the fabrication of semiconductor devices. They are used as a

protective overcoat, an interlayer dielectric for multilevel device, an alpha-particle

barrier, and an ion-implant mask. Polyimides provide the following advantages:

1. Polyamic acid and a few polyimides can be solution spun-coated upon a silicon wafer

to create a relatively planar surface that is suitable for the next level metallization for

multilevel IC packaging.

2. The thin film layer of photosensitive polyimide and/or polyamic acid formulation

spun coated can be further exposed, and etched with current processing equipment to

yield different patterns and micro texture images and circuitry.

3. The cured polyimide coatings are tough, resilient, and provides an excellent dielectric

properties.

Therefore, even though epoxy resin may still be the predominant packaging material

[240], the future prospect of specialized polyimides, for example, polyimides modified

by silicone, or fluorine containing groups, and fluoro-polyetherimides is very promising.

These polymers show exciting properties for packaging applications. These modified

polyimides possess good dielectric properties, lower moisture absorption, low CTE,

68

excellent thermal stability, high strength, and flexibility, etc. However, it is unlikely that

polyimides in general can displace epoxy resins in all microelectronics applications in

the near future owing to the problems of their high cost and processing difficulties.

1.1.7.6. Photo-sensitive polyimides [2, 16, 239-240, 243, 247-248,]

In the microelectronics industry, photo-sensitive resins are widely used in preparing

intricate patterns of IC and for multi-chip module fabrication. These materials contain

photo-crosslinkable groups which can be cross-linked under irradiation of energy of

certain wavelengths, thereby provides the capability of yielding patterns or image of IC

on the wafer. However, current photo-sensitive formulations have some disadvantages,

such as, low thermal stability, low strength, and some limitations in withstanding harsh

processing conditions during microelectronics wafer-fab operation.

Table-23: Major players in photopolyimides R&D and business world-wide [2, 16, 247].

(G- and I- lines corresponds respectively to the 436 & 365 nm lines of the photo stepper Mercury lamp)

Most polyimides tend to have superior thermal stability, excellent strength, good

dielectric properties, and good planarity with less pin-hole density, thus making them to

SUPPLIER Market Share (%)

TRADE MARK

FORMULATION REFERENCE

TYPE REMARKS

OCG (12%)

Selectilux Probimide Probimide

HTR3

Covalent Covalent Intrinsic

HITACHI-Du PONT MICROSYSTEMS

(44-50%)

Pyralin-PD

PL 2700 D PL2720 PL2730 PL2740 PL2750 PL1045 (NEG) PL1708 (NEG) PL2135 PL3708 (NEG) PL4235 PL5035 (NEG) PL6008 (NEG) PL8009 (POS) PL9009 (NEG)

Covalent Covalent Covalent Ionic Ionic Ionic Ionic Ionic Ionic Ionic Ionic Ionic Ionic Ionic

G-line Low Stress Low Stress I-line G-line, Low CTE I-line, Low CTE Low CTE I-line, Low CTE Low CTE G-line, High Resol. I-line, High Resol. G & I line (Aqu.Alk) G & I line (Aqu.Alk)

TORAY INDUSTRIES

(10%)

Photoneece

UR 3100 UR 3600 UR 3800 UR 4100 UR 5100

Ionic Ionic Ionic Ionic Ionic

Standard High Resolution G-line Low Modulus Low stress

ASHAI CHEMICALS (14%)

Pimel G Covalent Standard

SUMITOMO (5%) Sumiresin CRC - 6081 Ionic Standard

69

be most suitable material for such application R&D..

Since 1990s, the main applications of photosensitive polyimides (PSPI) are as stress

buffer or protective coatings for IC devices and as interlevel dielectrics for multichip

modules. The use of PSPI's is an emerging trend for microelectronics. Table 23 gives the

list of worldwide major business players as of December 1997 and their various types of

photosensitive polyimide products for microelectronics applications.

1.1.7.7. Membrane separation [2, 16, 133, 138, 140, 182, 249-256]

Membrane separation is one aspect of modern technology to separate and purify liquid

chemicals and gases. The polymer membranes made of polysulfone, cellulose acetate,

and polyamide are among the most prospective and widely used owing to their low cost,

ease of processability and high efficiency. However, since the last decade, the polyimide

based membrane has been considered to be a new generation membranes, because

polyimides not only offered outstanding thermal and mechanical properties, but also

provided an excellent gas separation performance.

In general, polyimides possess high selectivity, but low permeability. Obviously, the

permeability can be adjusted by a judicious combination of dianhydride and diamine in

the polyimide composition. Tables 24 and 25 shows the effect of the diamine and

dianhydride structures present in the polyimide on the gas transport and separation

properties of membranes.

Table-24: Effect of diamine structure on permeability of polyimides (in Barrers) [2, 15, 182]

Diamine H2 CO2 CO CH4 O2 N2 Temperature (oC) p-PDA* 9.4 2.75 0.064 0.60 0.105 35

p-ODA* 10.7 3.31 0.170 0.69 0.15 35

DATPA** 11.6 2.88 0.221 0.085 0.76 0.117 35 * Silicone-bridged dianhydride. ** ODPA is as dianhydride

Additionally, high selectivity and permeability of polyimide membranes could be

70

achieved by blending polyimide with other compatible polymers or by multi-layer

composite techniques. Chung, Vora and their coworkers have developed various fluoro-

polyimides based separation membrane technology [2, 16, 133, 138, 140, 182, 249-256].

Today, fluoro-polyimide membranes have been employed to separate and purify

hydrogen with high degree purity up to 99.99 % from syngas, enrichment of natural gas

and synthesis of ammonia. These membranes are also find use in the separation of

helium, carbon dioxide and acid gas, petroleum refinery and hydrocarbon vapors.

Table-25: Effect of dianhydride structure on permeability (in Barrers) and selectivity of polyimide membranes produced from ODA (diamine) and dianhydrides [2, 15, 182]

Dianhydride O2 N2 CO2 CH4 O2/N2 CO2/CH4 CO2/N2

PMDA 0.22 0.049 1.14 0.0265 4.5 43 23.23

BPDA 0.19 0.026 0.64 0.01 7.3 64 24.62

BTDA 0.19 0.024 0.63 0.01 7.9 63 26.25

SiDA 0.69 0.15 3.31 0.170 4.6 19 22.10

6FDA 3.9 0.73 16.7 0.341 5.3 49 22.88

Due to strong hydrogen bonding interaction between carbonyls in the imide structure

and proton in the water, polyimide membranes tend to possess high permeability for

water and a high separation factor for water/organic compounds. Thus, they are good

candidates for the removal of water from organic solvents. Table 26 lists the separation

properties of polyimide membranes for alcohol-water systems.

Table-26: Separation properties of membrane for alcohol-water system [182]

Membrane (µ) Q(kg m-2 h-1) α (H2O/EtOH)

Polyetherimide- ULTEM1000 0.03 507

Asymmetric poly(ether imide) 1.29 57

Chitosan 0.29 36

Perfluorinated ion-exchange membrane 2.45 2

1.2. FUTURE OF POLYIMIDES R&D

During the past five decades, numerous polyimide products with a variety of industrial

71

applications have been successfully introduced, such as, Kapton, ULTEM, XU-218,

PMR-49, NR-150, TORLON, Polyimide-2080, Vespel, and Pyralin 3002,

SIXEF-PI, DURAMID, etc. to name a few. Today such polyimides plays very

important roles in the fabrication of devices for aerospace, defense, consumer sports,

electronics, electrical, automotives, locomotives, life science/medical industry, etc.[1-7,

257]. High-temperature polyimides represented an attractive segment of business in the

plastics industry with an approximate sale of US $ 1080-millions in business by the year

2000 with an average 38 % of market share represented by the ‘value-added’ products

for the microelectronic industry [258].

Since the last decade, the high-temperature high performance specialty plastics

industry has been viewed as relatively mature and newer technologies are developing at a

slower pace. But this scenario is subject to significant change in the near future.

It must be noted here that for the future generation of polyimide-based materials, the

synthesis of appropriate aromatic dianhydrides and diamines with suitable functional

structures would be required. However, this would involve a major effort in part by the

specialty chemical industries. It is expected that new monomers and hence novel

polyimides, having improved performance, ease of processebility at lower cost will be

synthesized. Improvement in the ease of multi-steps complex processing technologies

will be another area where further R&D efforts are expected to be put forward.

Development of polyimide blends and its hybridization with other high performance

polymer will help to achieve materials with synergistic properties. Also, employment of

nano-scale materials technology and development of new polyimide nanocomposites

using inorganic materials will effectively lead to further improvement in materials

processing at reduce cost, without compromising the mechanical performance and

thermal stability. It is also expected that the efficient design of polyimides resin and its

72

alloy (blend), hybrids and nanocomposite and/or its formulations will be highly critical

for the delivery of an excellent performance at reasonable cost [165-166, 257].

Processing of some of the high performance polyimides is still a challenge for most

polymer engineers. Some of the fully imidized polyimides are often insoluble and

infusible, rendering them difficult to be processed. Current processing techniques for

polyimide are inadequate for future new generation of high-temperature polymers

requiring ultra high temperature processing [3, 5-7, 258].

Future commercial development of newer polyimides would also require to pay closer

attention to the applications of these polyimides for catering to the newer stringent

market demands. This new material requirement for next generation microelectronic and

aerospace applications may stimulate the synthesis of novel polyimides with special

functionality and material characteristics. For the niche high ‘value-added’ applications,

expensive polyimides may be considered acceptable, whereas for the consumer

applications, the solution lies in lowering the polyimide cost through polymer blends

without compromising the desired performance. The R&D in this direction would

enhance the technology competition for low cost monomers development or new

synthetic routes for polyimides [3, 5-7, 257].

For the niche industrial, micro electronics and electrical applications, it is expected

that the fluoro-polyimides would not only continue to provide key advantages over

conventional polyimides and polyetherimides, such as low dielectric constant, good

mechanical strength, thermal stability, lower flammability, lower moisture pick-up,

corrosion resistance and dimensional stability at elevated temperature, but also provide

an ability to fabricate with conventional equipment. New research advances in low

dielectric, high moisture barrier, high temperature stable polyimide based materials and

photoresists will play a major role in the improvement of device’s performance, and have

73

positive impact on furthering the trend of importance of polyimides for other high-tech

area from consumer lap top computers to critical medical devices. [3, 5-7, 257]

The electronic film represents a growing functional materials market opportunity for

flex circuit substrates. This market segment would offer the better potential to

synergistically leverage the existing and the future high performance fluoro-polyimide

materials into its films manufacturing activities, thus provide a ‘value-added’niche for

the functional microelectronics applications. Also there will be greater opportunities to

provide several laminated and coated products based on these fluoro-polyimide films

together with the high temperature adhesives. Without doubt, the most dynamic new

business opportunities will be in technologies associated with product-forms and parts

fabrication. Therefore, molded composites and or nano-composites parts for the high

temperature engineering automotive and rocket engines, etc. applications are another

significant areas where growing use of fluoro-polyimide is expected [3, 5-7, 258].

Effective selection and use of fluoro-polyimide compositions in fabrication of gas

separation membrane will lead to a state-of-the-art natural gas purification technology.

An eventual development of industry based on this membrane technology will

successfully provide concentrated natural gas feed stock with higher % of organics at

lower cost per cubic meter of gas to petrochemical industries. It will also be able to

provide methane enriched natural gas as higher BTU fuel to thermal power plant

worldwide economically and bringing down the energy cost for the consumers [256].

Speciality applications of high-temperature polyimides will be confined mostly to

aerospace, military and commercial airlines industries wherein a due consideration will

be given to performance of materials at pricing. The pricing of these materials will be as

usual in higher price range [2-7].

Worldwide increased terrorist activities, national and personal security, etc. problems

74

at home have fueled new high performance materials R&D activities by the defense

industries in USA with billions of dollars of new funding. Current U.S. president, George

W. Bush signed a ‘2003 Defense Spending (US$ 355-billions) Bill’ in October 2002,

which was approved and ratified by the U.S. Congress and the Senate in light of

increased worldwide acts of terrorism, and September 11th 2001 attacks at home. Out of

U.S. $ 355-billions, about U.S. $ 58-billions would be devoted only for research and

development of materials for the new generation of weapons and military hardware,

navel ships and air force fighter planes and star war weapons. It is the sharpest increase

in military spending for next fiscal year, and such spending will continue to increase

further for next decade. It is estimated that worldwide funding for military and civilian

R&D for such advanced high performance materials high-tech space station components,

highly sophisticated, radar evading military fighter planes, such as, shown in the Figure

29 [259], and hypersonic civil aviation aircraft development (Figures 5 & 6), etc. will

continue to grow for next 15 to 20 years, etc.

Figure-29: Under the DARPA funded project, the ‘Bird of Pray’, a highly sophisticated bat-winged highly classified stealth jet developed by US aerospace giant Boeing Co.’s ‘Phantom Works’[259], a military aircraft research and development division, under top secrecy, at a cost of about US 1-billion dollars. Each single-seat, single engine plane, which suppresses infra-red, radar, acoustic and visual signatures for revolutionary day light aerial warfare, if went in to production, it would cost about US 100 million dollars.

75

For electrical/electronics industries, new applications of fluoro-polyimides will

continued to be developed for the increasing miniaturization of microelectronic circuitry

and need of low dielectric inter-layers. It represents growing higher ‘value-added’

market. However, performance will dictate price [242, 258].

The cost-effective high-performance polyimides will continue to penetrate industrial

and automotive / transportation applications, but the price will be a deciding factor [258].

The R&D efforts will also continue through global joint venture, technology

collaboration requiring cooperative research through industry-government–academic

consortia, and cross licensing However, how the dominant economic events in the world

will influence the future R&D in high performance polymers including polyimides 15

years from now is remains to be seen. But, at least for the immediate next decade, it has a

solid growth potential.

1.3 SCOPE OF RESEARCH ON FLUORO-POLY(ETHER IMIDE)S (6F-PEI) PROJECT

As we have seen in the sections 1.1.2 through 1.1.5., and 1.1.7 that polyimides and

fluoro-polyimides are versatile engineering plastics having many desired properties to

classify them as high performance, high temperature stable polymers. Since the last 50

years these polymers has been used in various industrial applications. Today, the

chemistry of polyimides continues to be in the forefront of polymer science and

industrial R&D worldwide.

In retrospect, I have worked in US industries since 1980 in specialty polyimide-

siloxane and fluoro-polyimides R&D. I have invented, synthesized, developed

manufacturing process for several Poly(siloxane-imide) (PSI) and SIXEF-PI, and help

commercialize a number of such polyimide polymers for aerospace, electronic and gas

separation membrane applications prior to joining the Institute of Materials Research &

Engineering (IMRE) in 1997. At the institute, I continued to work on the synthesis and

76

study of novel fluoro-polyimide (6F-PI) for electronics and gas separation applications

until June 30th 2002, when I left the institute to join the National University of Singapore.

As of 1998 November, while working at IMRE, one of the objectives of my extensive

applied research activities was to carry out a parallel research on fluoro-polyetherimide

(6F-PEI) and fluoro-copolyetherimide (6F-CoPEI) polymers for my PhD thesis

requirements. These (6F-PEI)s and (6F-CoPEIs) that I have proposed to synthesize were

based on the polymer monomer composition approach scheme given in Figure 30.

X

Y OO


, etc.

CO

CCO

CCCF3

CF3

O

O

O

OC

OCC

OC

O O

O O

Where A = OR X

Aromatic Diamine

AND / OR


AND / OR Where X = Single bond, -CH2-,-O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

, etc.-Si(CH3)2-O-Si(CH3)2-,

Where Y= X

6F DianhydrideAromatic Dianhydride

Y OONH2NH2

Where Y = -SO2- , -C(CH3)2-, - C(CF3)2-

A

Aromatic Diether Linked Diamine

OR

Figure 30: Approach to monomer scheme for fluoro-polyetherimides compositions.

While working on my PhD research, it became obvious to me to simultaneously

develop a viable and comparatively better and cheaper fluoro-polyimides and its

technology. Thus I paid a very close attention to synthesize and develop (6F-PEI) and

(6F-CoPEI) materials having desired or better thermal [viz. higher glass transition

temperature (Tg), higher thermo-oxidative stability (TOS), etc.], and electrical [viz. lower

dielectric constant, etc.] performance for the electronic and aerospace application. My

objective was also to have these cheaper 6F-PEI and 6F-CoPEI’s properties equivalent or

77

better than the EYMYD, a [6FDA + BDAF] fluoro-polyetherimide which was

commercially available as poly (amic acid) [PEAA] solution until 1996 from Ethyl Corp.

Baton rouge, LA [142-144]; current commercially available conventional polyimide

KaptonH [40] from E. I. Dupont & Co., Wilmington, DE, and non-fluorinated

polyetherimide ULTEM1000 [46, 47], from General Electric Corp. Schenectady, N.Y,

USA. Therefore, keeping the properties of these three polyimides products in mind, I set

a target properties requirement as listed in Table 27 for the cheaper 6F-PEI and 6F-

CoPEI to be synthesized using commercially available monomers.

Table-27: Target properties of proposed fluoro-polyetherimide (6F-PEI) and fluoro- copolyetherimide (6F-CoPEI) polymer films.

PROPERTIES EYMYD

(Ethyl) PEAA

ULTEM1000 (GE ) PEI

Kapton H (Dupont)

PI

6F-PEI and

6F-CoPEI Target

Properties (Rohit Vora)

Tg (°C ).

267 220 407 250-300

TOS @ 315°C./300 Hrs. (% Wt. Loss)

< 8 % < 10 % 10 % < 5 %

Continuous Use Temp. (°C )

200 170 240 > 200

Dielectric Constant @ 10 MHz.

2.99 3.15 3.5 < 2.90

Moisture Uptake @ RT/24 Hrs. (%)

0.55 1.5 % 2.8 % < 0.7 %

Chemical Resistance to Acid & Base

Yes Yes Yes Yes

Tensile Strength (psi )

13,300 15,200 33,500 > 12,000

Elongation @ Break (%)

<10 % 60 72 > 10-100

Modulus (Kpsi)

353 430 430 > 400

CTE (ppm)

62 59.5 31.5 < 62

Process: Not Possible (N) Melt (M), Solution Cast (S)

(S) (M) (N) (M), (S)

The research for low-K polymers having higher continuous-use temperature with a

good hydrolytic stability and better processebility than above mentioned commercial

polymers has received significant attention from both academia and industry, therefore

78

another objective of my continuing PhD research was to develop a clear understanding of

chemical and physical, properties as well as thermal degradation kinetic of 6F-PEI and

6F-CoPEI films.

It is also known in the literature [260], that the molar group contribution method is

useful in calculating the estimated dielectric constant values of polymer, yet another PhD

research objective was:

o to use these empirical equations based on mathematical equations defined by

Lorentz and Lorenz and Vogel theories [260] for the estimation of dielectric

constants (electrical properties) of these 6F-PEI.

o to derive and expand these equations further to accommodate copolymers.

o to design new 6F-CoPEI compositions and estimate their dielectric constant

values well before they are actually synthesized in lab.

o to identify and synthesize only those polymers whose dielectric constant are

within my proposed target range for further study.

These objectives were successfully met through the synthesis of various 6F-PEIs and

designing of 6F-CoPEIs, their film fabrication, and characterization of various

properties. Chapters 2 and 3 report and discuss the finding of this research work.

Since the last 15 years, the ‘nano-scale’ technology has also become the focus of an

intense research. Well funded R&D activities are taking place at various research

institutes worldwide to develop various polymer/inorganic nanocomposites or hybrids

[166].

The polyimide polymers due to their high temperature stability, and high glass

transition (Tg) are ideal materials for such hybrid matrix/nanocomposites. Also due to the

reasonably good solubility of fluoro-poly(amic acid)s, the precursor of 6F-PI, in many

dipolar aprotic organic solvents, the fluoro-polyimides, and their esters or ionic salt

79

formulations are ideal candidates to be incorporated with inorganic materials, such as

organo-treated clay (i.e., organo-soluble clay) or minerals, inorganic salt, inorganic

oxides, organo-metallic compounds, etc. in the formation of nanocomposites.

For the fluoro-poly(ether imide)/inorganic nanocomposites materials, because of the

high Tg of polymer, it is expected that the agglomeration of nano-scale particles to large

particles and/or its phase separation would be prevented due to increased stabilization

(immobilization) of nano-scale particle in the polymer matrix. Hence, since February

2001, a third objective of my PhD research was to synthesize and characterize fluoro-

polyimide polymer and inorganic clay compound based nanocomposites materials.

Thus a series of fluoro-poly(ether imide) polymer [6FDA + p-SED]/Montmorillonite

(MMT) clay nanocomposites formulations having a varying percent of p-SED treated

MMT clay (Organo-soluble Clay) were synthesized, their films were prepared and

thermally cured, and characterized for their solution, thermal, mechanical and surface

properties. The result of this research is reported and discussed in Chapter 4.

The knowledge on the properties of (6F-PEI)s, (6F-CoPEI)s and nanocomposites

materials thus gained would be very valuable, and on the basis of which there exists a

scope for its further industrial applications development. In the future, the following

electronics and microelectronics applications of these fluoro-polyimides materials could

be developed by a commercial company under joint R&D collaboration project:

o Package encapsulant

o Base resin for photosensitive resist formulation

o Under-fill adhesives

o Interlayer protective (dielectric) coating

o Substrate for flexible circuit

It is hoped that once the current worldwide recession and economic downturn in

80

electronic and microelectronic sector is over, there will be an excellent potential for

establishing such a collaboration project with industries.

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94

CHAPTER - 2

SYNTHESIS AND PROPERTIES OF FLUORO-POLY(ETHER IMIDE)S

95

2.1. INTRODUCTION

2.1.1. Research background

Aromatic polyimides possess outstanding thermal, mechanical and electrical

properties as well as excellent chemical resistance [1]. The search for new polyimides

with improved processability and higher glass transition temperatures (Tg) than the

commercially available polyetherimide ULTEM1000 from GE Plastics, Schenectady,

New York, has received significant attention from both academia and industries since

high Tg polyimide KaptonH is only available as film from E. I. DuPont & Co.,

Wilmington, Delaware. It is also known that the structural rigidity of dianhydrides

contributes to the increase in the glass transition temperatures of those polyimides in the

range of 300 to 450 °C. Fully thermo-imidized polyimides are usually highly chemical

resistant, and do not dissolve in common organic solvents. Therefore, because of their

poor solubility in common solvents and high softening temperatures, the uses of some of

these polyimides in industrial applications, especially in microelectronics applications

are limited. Due to these limitations, and also due to the high Tg, many researchers

focused their research on the modification of the backbone structures of polyimides.

Their approach, such as an incorporation of a flexible ether linkage and meta oriented

phenylene rings into polymer backbone led to an increase in polymer chain flexibility

and solubility, but lowered the effective upper use temperature of these polymers [2-7].

For some niche electronic applications, the higher cost of polymer may not be the

determining factor. In fact, the premium performance would dictate premium price. The

continuous performance of a given polyimide at higher temperature processing

conditions and specific electrical and thermomechanical properties it imparts may justify

its higher price.

96

In the past it was shown that the incorporation of fluorine-containing moieties lowers

the dielectric constant and moisture absorption in the polyimide polymers [8-11]. Some

of these fluoro-polyimides were either patented or reported in the literature [12-32]. For

example, the fluorine-containing polyimide, SIXEF-33, i.e. [6FDA + 3,3-6F diamine]

and SIXEF-44, i.e. [6FDA + 4,4-6F diamine] of Hoechst Celanese Corp. Coventry,

Rhode Island, prepared from 2,2-bis(dicarboxyphenyl) hexafluoropropane dianhydride,

(6FDA), and 2,2-bis(3-aminophenyl) hexafluoropropane, (3,3'-6F diamine), and 2,2-bis

(4-aminophenyl) hexafluoropropane, (4,4-6F diamine) respectively, exhibited the high Tg

of 255 and 323°C respectively and excellent thermo-oxidative stability (>95% weight

retention) at 343°C (650°F) over 300 hours in air. Both these polyimides have low

dielectric constants of 2.55 and 2.58, respectively [12-25]. However, both SIXEF-33 &

SIXEF-44 were prohibitively expensive. Similarly, other fluoro-polyimide, i.e., fluoro-

poly(ether imide) [6FDA + BDAF] or [6F-BDAF] based on 2,2-bis(3,4-

dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and 2,2-bis[4-(4-

aminophenoxy)diphenyl] hexafluoropropane (BDAF) was developed and reported as

LARC-CP1 by NASA [9-10, 26-29]. It was commercialized in its precursor form, i.e.,

poly(ether amic acid) (6F-PEAA) through cross-licensing by Ethyl Corp. Baton Rouge,

Louisiana, USA [30-32] under the trade name of EYMYD. However, it too was very

expensive. Currently, all the three fluoro-polyimides are not available commercially.

2.1.2. Research objectives

The main objective of the present study was to develop high-performance

polyetherimides from commercially available monomers and study their structure-

property relationships. Keeping the properties of commercial polyimides products,

EYMYD, ULTEM1000 and Kapton H in mind, a research objective (target) of

97

desired properties requirement for the fluoro-polyether imide, i.e., (6F-PEI) for my PhD

research was set and listed in Table 1.

Table-1 : Target properties of proposed fluoro-poly(ether imide) (6F-PEI) and fluoro- Copoly(ether imide) (6F-CoPEI) polymer films.

PROPERTIES

EYMYD (Ethyl) PEAA

*

ULTEM1000 (GE ) PEI **

Kapton H (Dupont)

PI ***

6F-PEI and

CoPEI Target

Properties (Rohit Vora)

Tg (°C ). 267 220 407 250-300 TOS @ 315°C./300 Hrs. (% Wt. Loss) < 8 % < 10 % 10 % < 5% Continuous Use Temp. (°C ) 200 170 240 > 200 Dielectric Constant @ 10 MHz. 2.99 3.15 3.5 < 2.9 Moisture Uptake @ RT/24 Hrs. (%) 0.55 1.5 % 2.8 % < 0.7 % Chemical Resistance to Acid & Base Yes Yes Yes Yes Tensile Strength (psi ) 13,300 15,200 33,500 > 12,000 Elongation @ Break (%) < 10 % 60 72 > 10-100 Modulus (Kpsi) 353 430 430 > 400 CTE (ppm) 62 59.5 31.5 < 62 Process: Not Possible (N) Melt (M), Solution Cast (S)

(S) (M) (N) (M), (S)

* : [Reference # 30 to 32] ** : [Reference # 33] ***: [Reference #34]

To meet the research objectives, a series of poly(ether imide)s (PEI) based on aromatic

dianhydrides, including a fluorinated dianhydride and di-ether linkage containing

diamines having bis-trifluoromethyl group, sulfone and isopropyl groups were

successfully synthesized by a simplified one-pot, two-steps solution polymerization

process. The inherent viscosities of these poly(ether amic acid)s (PEAA) and poly(ether

imide), (PEI) polymers were determined. The thermal, electrical, mechanical properties

and crystallographic nature, thermo-oxidative and processing stability of the selected

fluoro-polyetherimide i.e. (6F-PEI) polymers were studied, and the results are discussed

in this chapter.

2.2 EXPERIMENTAL

2.2.1 Materials

Electronic grade powdered 1,2,4,5-benzenetetracarboxylic anhydride, i.e., pyromellitic

98

Dianhydride (PMDA), 2,2’-bis(3,4-dicarboxyphenyl)hexafluropropane dianhydride

(6FDA), 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA), 3,3,4,4-

benzophenonetetracarboxylic dianhydride (BTDA), 3,3,4,4-oxydiphthalic anhydride

(ODPA), 2,2-bis[4-(4-aminophenoxy)diphenyl] hexafluoropropane (BDAF), were all

received from Chriskev & Co., KS, USA; 4,4-bis(3-aminophenoxy)diphenyl sulfone (m-

SED) 4,4-bis(4-aminophenoxy)diphenyl sulfone (p-SED), and 2,2-bis[4-(4-

aminophenoxy) phenyl] propane (BPADE) were received from Wakayama Seika Kogyo

Co. Ltd., Japan;. N-methyl pyrrolidone (NMP), tetrahydrofuran (THF), N,N-

dimethylacetamide (DMAc), N,N-dimethyformamide (DMF), methylene chloride, β-

picoline, acetic anhydride, methanol, con. sulfuric acid and phosphorous pentoxide

(P2O5), were all received from Sigma–Aldrich, USA. All solvents except NMP were

used as received. The melting points of dianhydrides were checked by differential

scanning calorimetry (DSC) and were found to have sharp melting points (Table 1).

ULTEM1000 pellets were obtained from General Electric, Corp. NY, USA and its

films were prepared by solution casting. KaptonH Film of 25µm thickness was obtained

from E. I. DuPont & Co. DE, USA. The chemical structures of all commercially

available dianhydride monomers and diether diamine monomers used for the synthesis of

polyetherimide polymers are given in Table 2 and Figure 1 respectively. NMP was

always freshly distilled over P2O5 under reduced pressure and stored over pre-dried

molecular sieves and used when needed.

2.2.2 Polymerization

2.2.2.1 Synthesis of poly(ether imide) (PEI)

Several methods for the preparation of polyimides have been reported in the literature

[1-32, 35-50]. The most common procedure used in this investigation is a very simplified

99

Table-2 : Melting point (M. Pt.) of commercially available dianhydride monomers measured by DSC MONOMER

STRUCTURE NAME SOURCE

Lot #

Observed M. Pt. (°C)

Reported M. Pt. (°C)

COMMENTS

PMDA C

C

O

O

O

C

C

O

O

O

1,2,4,5-Benzenetetracarboxylic

anhydride (Pyromellitic dianhydride)

CHRISKEV, KANSAS, USA

# C9K003

287

290

Sharp M. Pt.

BPDA C

C

C

O O

O

OC

O

O

3,3,4,4-

Biphenyltetracarboxylic dianhydride


# S0748

300

302

Sharp M. Pt.

6FDA C C

C

C

CF3

O O

O

OC

O

CF3

O

2,2-Bis (3,4-dicarboxyphenyl)hexafluro

propane dianhydride


# 45177

243

247

Sharp M. Pt.

BTDA C

OC C

OCC

O

O O

OO

3,3,4,4-

Benzophenonetetracarboxylic dianhydride


# N/A

224

226

Sharp M. Pt.

ODPA C

OC C

OCO

O

O O

O

3,3,4,4-Oxydiphthalic

anhydride


# 42268

228

229

Sharp M. Pt.

99

100

one-pot, two-steps condensation polymerization synthesis process developed by the

author, which was also briefly discussed in Chapter 1, section 1.1.4 [24, 51-52]. The

reaction scheme is shown in the in Figure 2.

Figure-1 : Commercially available diether diamines For this study, 4 fluoro-poly(ether imide)s (6F-PEI) and 16 non-fluorinated poly(ether

imide)s (PEI) were synthesized, and their synthesis procedures are described as follows:

2.2.2.1.A Synthesis of fluoro-poly(ether imide) polymers

2.2.2.1.A.1 Synthesis of [6FDA + m-SED] fluoro-poly(ether imide) polymer

For example, in the case of synthesis of [6FDA + m-SED], which is a fluoro-

poly(ether imide) based on 2,2-bis (3,4-dicarboxyphenyl) hexafluropropane dianhydride

(6FDA) and 4,4-bis (3-aminophenoxy) diphenyl sulfone (m-SED).

2.2.2.1.A.1.a. Synthesis procedure

2.2.2.1.A.1.a.1. Step-1: Condensation polymerization procedure

As per the reaction scheme shown in Figure 2, accurately weighed 8.884g (0.02mole)

of solid 6FDA was added to an equimolar amount of m-SED diamine. (8.65g) pre-

dissolved in freshly distilled NMP to make 20% solid concentrations in a 250mL 3-neck

round bottom glass reactor set-up fitted with a variable speed mechanical stirrer and inert

S

NH2NH2

S

O

OONH2NH2

C

CH3

OO NH2NH2

CH3

C

CF3

OONH2 NH2

CF3

4,4-Bis (3-aminophenoxy) diphenyl sulfone [m-SED]

4,4-Bis (4-aminophenoxy) diphenyl sulfone [p-SED]

4,4-Bis (4-aminophenoxy) diphenyl propane [BPADE]

4,4-Bis (4-aminophenoxy) diphenyl hexafluoropropane [BDAF]

O

O

O O

O

101

gas environment (Figure 3). The reaction mixture was stirred under nitrogen at room

temperature for over 8-10 hours to make fluoro-poly(ether amic acid) (6F-PEAA)

solution, which was then imidized to form fluoro-poly(ether imide) (6F-PEI).

C C

CCF3

O

O

O

C C

CCF3

O

O

OH

C C

CCF3

O

O

N

+

n

n

[6FDA + m-SED] Fluoro-poly(ether amic acid) (6F-PEAA)

5 to 30% solid(NV) in NMPRT, 5 to 20 hr.

POLYMERIZATION

6FDA m-SED (Di-ether linked diamine)

Base CataystAcetic AnhydrideRT, 5 to 20 hr.( - 2H2O )


[6FDA + m-SED] Fluoro-poly(ether imide) polymer (6F-PEI)

CF3

CF3

CF3

C

C

O

O

N

C

C

O

O

O

C

C

O

O

HO

HN

HN

S O

O

O

NH3H2N O

S O

O

O

O

S O

O

O

O

Figure-2 : Synthesis reaction scheme for fluoro-poly(ether imide) [6FDA + m-SED]

2.2.2.1.A.1.a. 2. Step-2: Chemical imidization procedure

The phthalimide ring formation via cyclization can be achieved by either thermal or

chemical means. The thermal imidization process step is not feasible to convert bulk of

the poly(ether amic acid) in a reactor flask. Furthermore, the process is only good for

converting poly(amic acid) film (wet film) in to a solid polyimide film. The heating cycle

involves gradual heating of wet film to a very high temperature ( >300°C ) over a period

of time in flowing air or nitrogen atmosphere. Therefore, in these experimental studies,

102

Figure-3 : Laboratory scale glass reactor unit system for synthesis of polyimides

the chemical imidization was employed in which the amic acid was chemically

dehydrated in a condensation reaction with the removal of water (a by-product of

condensation reaction) by the addition of stoichiometric amounts of base and about 10 %

excess of dehydrating agent [24, 51-52]. The excess dehydrating agent facilitates the

maintenance of an anhydrous condition throughout the reaction. The base acts as a

catalyst. It also acts as an acid acceptor to accept organic acid formed due to the reaction

with water which was formed as a condensation bi-product as per the chemical

imidization reaction mechanism scheme shown in Figure 4.

The imidization reaction was carried out as follows: under nitrogen environment at

room temperature, 3.725g (0.04mole) of β-picoline (pKa 5.6) was charged to the

poly(amic acid) and stirred for 15 minutes to allow uniform mixing. Then 2.45g

103

(0.024mole) of acetic anhydride (~ 20% extra) was added drop-wise to the reaction

mixture over a period of 10 minutes.

CO

CCO

C

CCF3

CF3

O

O

O

O

CN

CCN

C

C

CF3

CF3

O

O

O

O

C OH

CC

C

CCF3

CF3

O

O

O

OHO

CH3COO

CO

H3C CO

CC

C

CCF3

CF3

O

O

O

OO C

OCH3C

OH3C

n

CO

CC

C

CCF3

CF3

O O

O

N

CO

CH3CO

H3C OO

N

Y OONH2NH2+

6FDADi-ether Linked Diamine

Y OOHNN

H

+ NR3

+ 2 [CH3COO HNR3]

n

H.

H.

(6F-PEAA) Fluoro-poly(ether amic acid)

Tertiary Amine base and an Organic Acid anhydride


(6F-PEI) Fluoro-poly(ether imide)

C OH

CC

C

CCF3

CF3

O

O

O

OHO n

Y OOHNN

Hn

Y OO

HN

HN

C O

CC

C

C

CF3

CF3

O

O

O

OO C

OCH3C

OH3C

nY OO

HN

HN

Y OO n

Tertiary Amine -Acetic acid Salt

CO

CC

C

CCF3

CF3

O O

O

N

CO

CH3CO

H3C OO

NH.

H.


Y OO n Y OO

+ 2 [CH3COO HNR3]Tertiary Amine -Acetic acid Salt

Where Y = -SO2- , -C(CH3)2-, - C(CF3)2-

Figure-4: Mechanism for chemical imidization of fluoro-poly(ether amic acid) to fluoro-poly(ether imide) The reaction mixture was stirred under nitrogen at room temperature for another 8-10

hours to get (6F-PEI) polymer solution mixture. This (6F-PEI) polymer and a small

sample of the (6F-PEAA) were then precipitated with 2000mL of methanol and copious

amount of de-ionized water respectively and dried at 100oC overnight in an air

circulating oven.

SO

O

OO

CC

C

C

CF3

O O

O

N

CF3

n

[6FDA + m-SED] Fluoro-poly(ether imide) (6F-PEI)

C

O

N

Similarly, the other fluoro-poly(ether imide)s (6F-PEI) were synthesized as given in

104

Appendix-A. In all the cases, both (6F-PEAA) and (6F-PEI) polymers were

characterized by FT-IR.

2.2.2.1.B. Synthesis of non-fluorinated poly(ether imide) polymers

Several non-fluorinated poly(ether-imide)s (PEI) were synthesized using non-fluorine

containing dianhydrides as per the reaction scheme shown in Figure 5.

Figure-5 : Synthesis scheme of non-fluorinated poly(ether imide)s

2.2.2.1.B.1. Synthesis of [PMDA + p-SED] poly(ether imide) polymer

In the case of synthesis of [PMDA + p-SED], which is a non-fluorinated PEI based on

1,2,4,5-benzenetetracarboxylic dianhydride [i.e. pyromellitic dianhydride (PMDA)] and

4,4-bis (4-aminophenoxy) diphenyl sulfone (p-SED), the above procedure was repeated

with the following materials and quantities (Table 3) employed.

Similarly, the other non-fluorinated poly(ether imide)s (PEI) were synthesized as

given in Appendix-A.

C

O

CC

O

C

O O

O O

Y OONH2NH2

C

NH

CC

HN

C

O O

O O

Y OOOH

C

N

CC

N

C

O O

O O

Y OO

A +

Where Y = -SO2- , -C(CH3)2-, - C(CF3)2-

AHO

n

An

Poly(ether amic acid) (PEAA)

5 to 30% solid (NV) in NMPRT, 5 to 20 hr.POLYMERIZATION

DianhydrideDiether Linked Diamine

Base Catayst/ Acetic AnhydrideRT, 5 to 20 hr.

IMIDIZATION

Poly(ether imide) Polymer (PEI)

105

Table-3 : Monomers and chemicals used for the synthesis of [PMDA + p-SED]

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) PMDA 218.12 100 0.04 8.7248 p-SED 432.50 100 0.04 17.300 NMP (@ 20 % solid NV) 104.10 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.900 Methanol 3000 ml

S

O

OO

C C

C

O

O

N

n

O

O

NC

O

[PMDA + p-SED] Poly(ether imide) (PEI)

2.3. FABRICATION

2.3.1. Polymer film preparation

There are a number of commercial film products produced by solvent casting with a

fairly wide variety of applications ranging from electrical, electronics, solar films, and

adhesive coated tapes for automobile trim etc. [53]. For many polymeric materials which

are not melt processable, but soluble in organic solvents, as in the case of many

polyimides, solvent casting is the only way to prepare polymer film. The author

developed a special film casting technique [24], which was used in this study. Solutions

of selected fluoro-poly(ether imide)s and ULTEM1000 were made at 15% solid

concentration level in NMP and pressure filtered through a 0.5µm filter under a nitrogen

atmosphere. Filtered solutions were then coated on glass plates using a doctor blade

(Gardner Film Casting Knife, Model AG-4300, Pacific Scientific, USA) with an

adjustable gate clearance, controlled with a precision micrometer, from 0 to 6250µm gap.

The films were dried in a nitrogen environment, and then heated gradually as per the

stepwise thermal heating cycle as shown in Figure 6, in a programmable oven up to

250oC at a heating rate of 1oC /min and held at 300oC for 1 hour. After heating, the films

were allowed to cool down gradually to room temperature. The self-supporting flexible

106

films were lifted up from the glass plate by soaking in water and dried with a lint free

paper (Kim wipe) towel and further dried in an oven at 150oC for 30 minutes to obtain 20

to 35µm thick films. The films of KaptonH (as received 25µm thick) and

ULTEM1000 were used as 'the control'.

Figure-6 : Thermal curing program for (PEI), and (6F-PEI) films [24] 2.3.2. Poly(amic acid) films fabrication for FT-IR analysis: Using the above procedure, filtered 20% non-volatile (NV) poly(ether amic acid)

(PEAA) solution in NMP was coated on the glass plate using doctors blade to get a

uniform thin wet film. Then the glass plate was carefully and gently dipped into a Pyrex

(Dow Corning) glass rectangular baking tray containing de-ionized water. The color of

the wet PEAA film changed from colorless (transparent) or pale yellow to opaque white

due to precipitation of polymer in water since poly(amic acid)s are hydrophobic in

nature. Thin white color solid PEAA film was then gently lifted off the glass plate and

washed with copious amount of de-ionized water for about 30 minutes. Film was gently

wiped dry by lint-free tissue paper (Kim wipe). Then it was further dried in an air

circulation oven at 80°C for 15 minutes to get rid of adsorbed water on the surface of the

film. This film was then stored in a desiccator over dry-rite until used for FT-IR

Film Curing Cycle80°C

80°C

110°C150°C

150°C

110°C

200°C

200°C

250°C

250°C

1 HR

1 HR

1 HR

Circulating air environment in programmable oven

Gradual cooling to RT

1 HR1 HR

1 HR1 HR

RT55°C

55°C

300°C

300°C


80°C

110°C150°C

150°C

110°C

200°C

200°C

250°C

250°C

1 HR

1 HR

1 HR



1 HR1 HR

1 HR1 HR

RT55°C

55°C

300°C

300°C

107

spectroscopy study. A small amount of PEAA film was grounded and mixed with KBr

and compressed to a 1 cm round disc which was used for FT-IR analysis.

2.3.3. Thin polymer plates by compression molding The thermoplastic fluoro-poly(ether imide)s based on 6FDA and 4,4-bis(4-amino

phenoxyphenyl) sulfone (p-SED), i.e., [6FDA + p-SED], 4,4-bis(3-

aminophenoxyphenyl) sulfone (m-SED), i.e., [6FDA + m-SED], 2,2-bis[4-(4-amino

phenoxy)phenyl] propane (BPADE), i.e., [6FDA + BPADE] and 2,2-bis[4-(4-

aminophenoxy)diphenyl] hexafluoropropane (BDAF), i.e., [6FDA + BDAF] were

compression molded in a 10x10cm square special steel alloy mold between heated

platens of a Karver hydraulic press [the press was fitted with 30x30cm square platen

having internal heating elements (Karver & Co, USA)] at 320°C at 500psi for 7 minutes.

Light yellowish to yellow color transparent rectangle plate of 1.0 to 1.5mm thickness

were obtained.

2.4. CHARACTERIZATION

2.4.1. Solubility of solid polymer

Solubility of solid poly(ether imide) was determined by preparing a 2% wt. solution in

a small capped vials. The solutions were stirred vigorously with magnetic stirrer bars at

room temperature and at slightly warm (~35°C) temperature. The solutions were visually

checked for the un dissolved residue for 24 hours and the observation on level of

solubility such as full, partial, insoluble, etc. was recorded.

2.4.2. Viscosity of polymer

The solution viscosity is a measure of the size or extension of polymer molecules in

space. The principle of viscometry is based on the determining the efflux time t required

for a specified volume of polymer solution to flow through a precision capillary tube of a

viscometer [Figure-7] which has been calibrated using liquid compound of known

108

viscosity and density, and compared with the corresponding efflux time t0 for the solvent.

However, the precision of measurement varies with sample type, solvent and

experimental conditions used. Typically precision varies from 1-5% [54].

Figurer-7 : Capillary viscometers commonly used for measurement of polymer solution viscosities Molecular weight is related to the viscosity of polymer solution. The molecular

weights of polymers have been correlated to the viscosity at specific solvent and

temperature condition at specific sample concentration. Therefore, by knowing the

intrinsic viscosity [ηint], one could easily determine the molecular weight of polymer by

using Mark-Houwink-Sakurda equation:

(ηint)= K. vMa (1)

where vM is the viscosity-average molecular weights

Both K and a are empirical (Mark-Houwink) constants that are specific for a given

polymer, solvent and temperature.

For this research work, no attempt was made to determine the molecular weights of

polymer by using above equation as GPC results were sufficient for the correlation.

Inherent viscosity [(ηinh), a logarithmic viscosity number] was calculated using the

following equation: (ηinh) = ln (t/t0 ) (2)

C

Where t0 is flow time of solvent

t is flow time of solution and

C is the concentration of the sample in g/ dL.

109

0.25g of solid polymer was dissolved in 50mL of solvent (NMP) in a volumetric flask

to get a concentration of 0.5g/dL. The solution was filtered (Whatman filter paper)

before being filled into the viscometer.

The inherent viscosities (IV) (ηinh) of the PEAA, (6F-PEAA), (PEI) and (6F-PEI)

polymers were measured according to ASTM 2515 / D446 in NMP at a concentration of

0.5g/dL at 20°C using a modified Cannon Fenske viscometer and using the above

equation. The average of three readings was taken for calculation.

2.4.3. Fourier transform-IR (FT-IR) spectroscopy

Fourier transform infrared spectroscopy (FT-IR) is used for the identification of

organic, inorganic compounds, and polymers. For organic polymers, the groups of atoms

such as –CN, -NO2, -SO2, -OH, -CO2, -CH3, –COOH, -C6H5, etc. would absorb the

energy in the infrared region at specific and predictable frequencies, thus allowing the

identification of the specific functional groups within molecules relatively easy. The

typical spectral analysis of the unknown spectrum is made by correlating group’s

absorbing frequencies, relative intensities, and comparing with the reference spectra of

known compounds. In most cases this is far superior in speed and accuracy than the

classical chemical methods. The FT-IR is a very powerful tool for characterization of

polyimides. It can be used for both solid and solution samples. FT-IR uses an

interferometer to observe the spectral resolution elements simultaneously, rather than

scanning through gratings and prism to disperse the infrared radiation. The advantage,

resulting from such changes were increased light throughput, speed, and detection

sensitivity [55]. The group absorption changes for chemical compounds are very easy to

determine using FTIR. Some useful group absorptions for polyimide, poly(amic acid)

and anhydrides are listed in literature [56-59].

The FT-IR spectra of the (PEAA), (6F-PEAA) films, and (PEI) and (6F-PEI) solids

110

were obtained using Perkin Elmer FTIR model with Spectrum 2000 software, and a film

holder and/or NaCl disk. The scanning range was from 4000 to 400cm-1.

2.4.4. Gel permeation chromatography (GPC) [a.k.a. Size exclusion chromatography (SEC)] To improve physical and thermomechanical properties of a polymer, it is important to

control its molecular weight and the molecular weight distribution during

polymerization. Gel permeation chromatography (GPC) [a.k.a. size exclusion

chromatography (SEC)] is one of the quickest methods to obtain relative molecular

weights, and its distribution. GPC is also used to detect the number of components as

well as branching in polymer sample, and to get information about polymer

conformation and co-monomer distribution as a function of molecular weight. The main

use of GPC is to obtain quantitative information about oligomers and polymers having

molecular weights relative to a polystyrene standard (an internal reference) within the

range of a few hundred to a few hundred thousands. GPC is a method which separates

molecules on the basis of their hydrodynamic volume or size (it is true only when there

is no interaction between the column packing resin and the polymer sample). This is

achieved by passing the polymer sample through a set of columns packed with porous

resinous particles (referred to as the stationary phase) of controlled pore size. Molecules

having smaller sizes will diffuse deeper in to pores of stationary phase, whereas, the

larger molecules will have a lesser tendency to diffuse. As a result of this diffusion

phenomenon, the order of elution is based on the hydrodynamic sizes (or molecular

weights of polymer species) of the molecules. Hence, the larger molecule elutes faster.

Since columns packed with different pore size resin are available, GPC is capable to

investigate a wide range the molecular sizes from a very wide to narrow, depending on

the appropriate selection of column. Typically, GPC is equipped with a detectors (e.g.,

UV/Visible, refractive index (RI), etc.), which when interfaced to a differential

111

viscometer. A universal calibration curve correlating the product of the intrinsic viscosity

and molecular weights with retention time can be obtained for a set of pre-selected

polystyrene standard [60-61].

Fully thermo-imidized polyimides usually do not dissolve in common organic solvent

as they are solvent resistant. Besides, the GPC measurement of polyimides were further

complicated by strong interaction between polar polymer, solvent and also with

stationary phase due to presence of polyelectroclyte effect [62-64]. However, such effect

can be minimized or suppressed by adding electrolytes salt such as LiBr or H3PO4 into

mobile phase and polymer sample dissolved in such eluent mixture [63-64].

The molecular weights of (PEI) and (6F-PEI) were determined using a Waters GPC

system containing Waters 2690 separation module and Waters 2487 UV detector. The

system was calibrated using 10 narrow molecular weight distribution polystyrene

(Polysciences Corporation, USA and Polymer Laboratories USA) standards having wide

molecular weights range as given in Table 4.

Table-4 : Molecular weights of polystyrene standards used for GPC calibration

GPC CALIBRATION

Calibration Standards

(POLYSTYRE)

Mol. Wt.

1 2000,000 2 900,000 3 488,000 4 400,000 5 320,000 6 200,000 7 80,000 8 30,000 9 12,900

10 4000

Three Gelpack GL-S300MDT-5 (Hitachi) columns of size 8x300mm, packed with

polystyrene gel having an exclusion limit of 2x108, were connected in series, and housed

112

in an oven maintained at 40°C. Mixture of THF: DMF (1:1) containing 0.06M LiBr and

0.06M H3PO4 was used as mobile phase to suppressed a polyelectrolyte effect typically

observed for poly(amic acid)/polyimides type of polymers. The mobile phase was

filtered through 0.2µm PTFE filter (Millipore). The UV detector was used over IR

detector, simply because, for the above mobile phase mixture UV detector is very

sensitive and provides high resolution, and also a stable base line. Conditions used were

wavelength 270nm, flow rate 1mL/min, injection volume 200µL and sample

concentration 1mg/mL. The polymer samples were pre-dissolved in above eluent mixture

and filtered through 0.45µm PTFE-PP 13mm filter (Lida Manufacturing) just prior to

injection. Data were acquired from the Waters 2487 UV detector using Millennium 32

software. The all the relative molecular weights [ nM , wM and Polydispersity (d)] were

calculated against the above polystyrene standards.

2.4.5. Density of polymer film

The densities of dry polymer thin plates were measured by AG204 Delta-Range

Mettler Toledo with a density determination kit using the displacement technique [65].

The samples were cut into 30×20mm. Before the measurement, the samples were dried

in a vacuum oven overnight at 120oC to remove absorbed water. At the room

temperature of 20oC, the weight of dry sample was W1, whereas the weight of the dry

sample immersed in ethanol solvent was W2, and ethanol solvent density at 20oC was

0.78934. The polyimide sample density was obtained from the equation:

( ) 78934.021

1

WWW

−=ρ (3)

The densities ρ (g/cm3) of polymer samples were determined and reported in Table 5.

2.4.6. Hydrolytic stability

Moisture absorption measurements of thin films samples of (PEI) and (6F-PEI) were

113

calculated from the difference in weight of pre-dried and wet film with an ultra

microbalance from Sartorius (model YDP-03-OCE) with weight reading range of

0.001mg to 5.1g. The film samples were pre-dried at 150°C for 1 hour before weighing

accurately and dipped completely in de-ionised water in a vial. The vials were sealed

immediately and maintained at 50°C for 100 hours. After which the samples were taken

out of vials and dried by lint free tissue paper (Kim wipe) and re-weighed immediately.

2.4.7. UV-VIS spectroscopy

The absorbance or transmission of UV-Visible light frequency is affected by the

specific functional group in polymer. Thus % transparency of unknown film sample may

be determined by comparing its transmittance with that of standard (air) under same

experimental conditions, wavelength, temperature, etc.

The % transparency of visible light at 500nm of the (6F-PEI), ULTEM1000 and

KaptonH films was determined by a Shimadzu UV-VIS Spectrophotometer model UV-

2501 (PC)S with RS658 photomultiplier tube. The films were scanned from 200nm to

550nm at ambient condition against ‘blank’ (air) used as reference medium. The spectral

data were recorded automatically by a programmed computer, and % transparency of

(6F-PEI) films was compared against the % transparency of ‘control’ ULTEM1000 and

KaptonH films.

2.4.8. Differential scanning calorimetry (DSC)

DSC is a technique for studying the thermal behaviour of materials as a function of

temperature. They undergo physical or chemical transformation with absorption or

evolution of heat or with a change in heat capacity. A glass transition (Tg) will be

recorded as a more or less sudden increase in heat capacity. Melting and crystallization

are recorded as endothermic and exothermic peak, respectively. Integration of these

peaks permits quantification of the transition. Glass transition is the property of only the

114

amorphous portion of a semi-crystalline polymer in which the polymer undergoes

transformation from rubbery to glassy phase [66].

Glass transition temperatures (Tg) of (PEI) and (6F-PEI) films were determined from

the second heating cycle using a differential scanning calorimeter model DSC-2920 from

TA Instruments with Pyris software. Scans were run at a heating rate of 10oC/min in

flowing nitrogen (10cc/min) condition. Temperature scanned was in the range of 50 to

425°C in the heating cycle and from 425 to 50°C in the cooling cycle. Temperature and

heat flow were calibrated using pure indium as a standard.

2.4.9. Thermogravimetric analysis (TGA)

TGA technique determines the change in polymer sample weight as a function of

temperature (Dynamic TGA) at a constant heating rate. It can also be used to study the

change in sample weight as a function of time at a constant temperature (Isothermal

TGA). The analysis can be performed in nitrogen, air, etc. [66].

Thermal decomposition temperatures (5% wt. loss) of (PEI) and (6F-PEI) films were

examined using dynamic TGA [model Perkin Elmer TGA-7 with Pyris software]. Scans

were run at a heating rate of 10oC/min in flowing air atmosphere (10 cc/min). The %

char yield was determined in flowing nitrogen atmosphere (10 cc/min) at a heating rate

of 10oC/min from 100 to 1000oC.

2.4.10. Thermo-oxidative stability (TOS)

Long-term isothermal, thermo-oxidative stability (TOS) studies of (6F-PEI) and

commercially available ULTEM1000 and KaptonH film samples were performed in

air for 300 hours at 315oC (600oF) in a Lenton programmable forced air oven with

Eurotherm 2408 Temperature controller/programmer from Lenton Thermal Design, UK.

The details of procedure used is reported in discussion section.

115

2.4.11. Dynamic mechanical analysis (DMA)

DMA is used to measure the dynamic modulus and damping of polymer material

under oscillatory load as function of temperature. The DMA uses the principle of forced

amplitude for measuring the viscoelastic properties of sample as a function of

temperature. Most polymers show viscoelastic behaviour in which a portion of the

deformation energy is dissipated in other form of energy such as heat. The DMA

compensates for this energy loss by a in-phase drive signal which keeps the sample in a

continuous natural frequency oscillation, and maintain a constant amplitude. The size of

the force needed for constant amplitude is a measure of sample’s energy dissipation

(damping). The other measured parameter is the resonant frequency. From these data, the

storage modulus G', Tan δ and loss modulus E" of polymer film samples can be

determined [66]. Dynamic Mechanical Analyzer (DMA) [model TA-DMA-2980 from

TA Instruments] was used. Polymer film samples of size 10mm in length and 2mm in

width were subjected to temperature scan mode at a heating rate of 3°C/min. in air at a

frequency of 1Hz, and an amplitude of 0.2mm were used in current measurement of (6F-

PEI) films.

2.4.12. Thermal mechanical analysis (TMA)

TMA is a technique in which the deformation (dimensional change) of a polymer film

sample is measured under non-oscillatory (static) load as a function of controlled

temperature change rate. Stress can be applied to the sample during analysis. The TMA

can be run with penetration (or compression) or an expansion probe. In compression

mode under controlled temperature change rate, due to its high sensitivity to dimensional

change, the glass transition temperature (Tg) is more accurately determined for film

sample as compared to Tg measured by DSC for the identical sample [66].

116

2.4.13. Coefficient of thermal expansion (CTE)

The coefficient of thermal expansion (CTE) values (m/m°C) were determined by

Thermal Mechanical Analyzer (TMA) [model TMA-2940 from TA instruments] at

heating rate of 5°C/min in air (ASTM method D 696).

2.4.14. X-ray diffraction (XRD)

The X-ray diffraction can qualitatively provide information on the crystallographic

nature (structure), molecular packing and orientation of polymer chains in bulk samples,

fibers and films. It is one of the best techniques to determine the crystalline-amorphous

nature of polymer sample. The degree of crystallinity of polymer sample is measured as

the ratio of the crystalline component to total scattering from both the crystalline and

amorphous components. A beam of monochromatic X-rays with wavelength λ is incident

on to the polymer sample, and by virtue of the crystallographic atomic arrangement in

the polymer, the X-rays are diffracted at various discrete angles (2θ) when the Bragg

condition is satisfied. The crystallographic interlayer spacing (d-spacing) solely depends

on the lattice structure and the unit cell size. The intensity of the peak depends on the

atomic arrangements within the cell [67].

The X-ray diffraction measurements of compressed disks of solid (6F-PEI), and

ULTEM1000 of average thickness 1mm, and KaptonH films were carried out at room

temperature in reflection mode in order to better understand the structure (i.e. chain

orientation and order) effect on the solubility and glass transition property. An X-ray

diffraction unit (Phillips model PW 1729-10) fitted with Cu - Kα radiation (30kV,

20mA) with wavelength λ of 1.54Å was used. The scanning rate was 0.5°/min at ambient

temperature. The spectral window ranged from 2θ = 5° to 2θ = 40°. The diffraction

patterns of intensity versus two theta (2θ) were automatically recorded with computer

117

software. Corresponding interlayer d-spacing value was calculated from the diffraction

peak maximum, using the Bragg equation:

d = λ/2 sinθ. (4)

2.4.15. Mechanical properties

The physical properties of a solid polymer are determined under a variety of loading

and test environmental conditions. Continum mechanics provides mechanical testing

with an analytical tool for understanding polymer’s behaviour and performance which

are interpreted in terms of stress-strain states. The polymer film or bar specimens are

loaded at a constant rate of deformation and stress-strain data are collected continuously.

Most polymers exhibit viscoelastic behaviour. Thus, the stress-strain data are time and

temperature dependent and therefore, also dependent on rate of loading. From the

analysis of these data mechanical properties such as Young’s modulus, (which is a

measure of rigidity), ultimate stress at break (a measure of strength), ultimate

deformation (elongation) at break and other properties can be calculated [68].

The mechanical property of compression molded plates of (6F-PEI), and films of

ULTEM1000 and KaptonH were determined by Instron Mechanical Analyser Model

5542. using a 0.25cm wide and 8.0cm long sample with the clamp distance of 4.0cm.

2.4.16. Dielectric analysis (DEA)

Most unmodified polyimides are excellent insulator of electric current due to high

resistivity and practically no conductance as shown in Figure 8 [69].

Various factors influence such resistive behaviour of polymer. These factors are

chemical structure, polarization of groups in polymer chain, polymer morphology and

porosity, hydrophilicity or hydrophobicity, temperature, impurity or contaminant within

and on its surface. The electrical properties that have to be considered when selecting a

118

polymeric material for electrical or electronics insulation coating applications are

dielectric constant, dielectric strength, volume resistivity, surface resistivity, dissipation

Figure-8 : Typical ranges of electrical conductivity of polyimide and other inorganic metal and semiconductors [70] factor, and arc resistance [69]. It is also understood that these properties are affected by

the external factors such as temperature, operating frequency and voltage electric field,

and other environmental variables.

First let us understand the importance of response of polymeric materials under an

applied electric field. When a polymer film is placed between the parallel plates of the

dielectric analysis (DEA) instrument and the electric filed is applied, the net result of

which causes polarization of polymeric materials through displacing the positive and

negative charges within the atoms in the molecules of the polymer in the opposite

direction, and thus the whole materials consequently become electrically polarized [71].]

The electric polarization of polymeric materials is in fact an electric dipole moment

per unit volume, and is defined as

P = Np (5)

where

P is dipole moment per unit volume of polymer (measured as coulombs per

square meter)

Resistivity

10 8 10-18 10 410 210 - 610 - 810-10 10-14 10-16 10 610 - 210 - 4 1

1018 10- 410- 210 81010101210 1410 16 10- 610 210 4 10- 81

PolyimideFused Quartz

SulfurDiamond

CopperGlass

Silver

Aluminum

Platinum

Bismuth

10 6

Germanium (Ge)Silicon (Si)

Gallium Arsenide (GaAs)

Gallium Phosphide (GaP)

Cadmium Sulfide (CdS)

10 -12

Conductivity σ ( Ω cm ) -1 -1

ρ ( Ω - cm )

ConductorSemiconductorInsulator

119

N number of atom per unit volume

p is the dipole moments of individual atoms per unit volume

The dielectric constant (ε′) can be expressed as

ε′ = P / ξ (6)

where

ξ is the applied electric filed, and is defined as the voltage applied per unit meter

[71].

For practical purpose, the dielectric constant of a polymeric material is also defined as

the ratio of capacitance Cp of a capacitor having given polymeric material to the

capacitance Cv of the same capacitor in vacuum.

ε’ or K = Cp / Cv (7)

where

ε’ or K is dielectric constant or also known as permittivity.

The dielectric constants of polymers are due to their electronic polarizability and the

presence or absence of polar groups in polymer’s molecular structure. Polymer with

polar groups have larger dipole moments and large dielectric constant since their dipole

are able to orient in the applied electric field. The dielectric analysis of polymer is

therefore based on the interaction of polar groups on the polymer when subjected to a

high and/or low electric filed. For insulation applications, polymers without polar groups

are preferred. As mentioned above, the good insulator exhibits very high resistivity, i.e.,

the current passing through them is extremely low.

The volume resistivity is calculated from the voltage, current and geometric

configuration of the polymer film sample, and the electrodes used [69]. The dielectric

120

constant of polymers varies with the applied frequency and would increase or decrease

depending upon the molecular structure, and the presence of any additives or fillers.

The dissipation factor of a polymeric material is defined as the ratio of the current of

the resistive component to the current of the capacitive component and it is equal to the

tangent of the dielectric loss (tan δ) [72].

The dielectric strength of a polymer is its ability to withstand high voltage current field

without breakdown. It is defined as the maximum voltage below which no breakdown

occurs. Whereas, the breakdown voltage is defined as the maximum voltage above which

actual failure occurs [73].

For the dielectric property measurements of (6F-PEI), ULTEM1000 and Upilex-S,

their films were sputter coated with ultra thin gold layer via vacuum evaporation

deposition for 40 seconds using JFC-1200 Fine Coater model fitted with FC-TM10

Thickness Monitor [from JEOL] on the both sides. The gold-coated film was then placed

between upper and lower thin film sensors parallel plates in the furnace of DEA unit

model DEA-2970 from TA instruments]. To ensure proper electrical contacts, 450N

(Newton) force was applied on the sample. In order to avoid the moisture effect on the

dielectric property, a new approach was used to evaporate off any moisture condensed on

the sample by heating it in the DEA furnace to a higher temperature around 150oC in

flowing nitrogen. After which it was cooled down to 25oC and then measurement was

taken at a frequency from 1 Hz to10 MHz at and at 50% relative humidity at temperature

of 25°C in a flowing nitrogen atmosphere condition. The dielectric constant (ε’) was

automatically calculated and recorded by the machine as a function of frequencies..

2.4.17. Rheology

Dynamic mechanical spectroscopy of solid polymer sample is very useful for the

prediction and correlation of the time and temperature dependent stiffness, as well as for

121

polymer melts, the viscoelastic properties under steady shear melt flow condition.

Figure-9 : Chemical structure of repeat unit of fluoro-poly(ether imide) (6F-PEI), ULTEM1000, and KaptonH polymers The steady shear melt viscosity and normal stress difference are measured by torsional

flow between parallel plate of the Rheometric mechanical spectrometer. The data at low

shear rates (or frequencies) are more sensitive to difference in molecular structure than

are the high shear rate data obtained by capillary viscometry [74].

Rheometric mechanical spectrometer (model ARES-605) with two parallel plates

having geometry of 2.54cm, and operating frequency in the range 0.001 to 100 radian per

C

CH3

C

CH3

OO

CH3

CC

C

C

CF3

O O

O

NC

O

S

O

O

OC

C

C

C

CF3

O O

O

NC

O

CN

C

O

O

CN

C

O

O

O O

CH3

CF3

CF3

C

C

C

O O

O

NC

N

O

C

CF3

OOCF3

CC

C

C

CF3

O O

O

NC

O

CF3

S

O

OC

C

C

C

O O

O

NC

O

CF3

n

N

n

ON

n

n

N

n

N

KaptonR-H Polyimide : [ PMDA + ODA]

ULTEMR-1000 Poly(ether imide) : [BPADA + m-PDA]

(6F-BDAF) Fluoro-poly(ether imide) : [ 6FDA + BDAF]

(6F-BPADE) Fluoro-poly(ether imide) : [ 6FDA + BPADE]

(6F-m-SED) Fluoro-poly(ether imide) : [ 6FDA + m-SED]

(6F-p-SED) Fluoro-poly(ether imide) : [ 6FDA + p-SED]

OCF3

n

O

O

122

second (rad/s) was used to determine melt rheology and processing stability at 50°C

above Tg. The system was connected to an IBM PC through interface for data acquisition

(6F-PEI). Polymer solid samples were first molded into disk and melted between the

parallel plate test fixtures of the Rheometer with the minimum exposure to air. The

polymer’s complex viscosity was measured as a function of time for 30 minutes at a

frequency of 1 rad/s.

2.5. RESULTS AND DISCUSSION

2.5.1. Properties

The properties of a series of poly(ether imide) (PEI) prepared from the listed

monomers by one pot, two-step method (Figure 2 & 5) are given in Tables 6 through 12.

The chemical structures of the repeat units of the (6F-PEI) of interest, ULTEM1000

and KaptonH are shown in Figure 9.

2.5.1.1. Poly(ether imide)’s chemical structural characteristics

The FT-IR spectra in Figure 10 clearly indicated the imide ring formation and the

disappearance of the amide peaks during the chemical cyclization step. For example in

the case of (6F-PEI), based on 6FDA and m-SED, (i.e. [6FDA + m-SED], the FT-IR

spectra of fluoro-poly(ether amic acid) (6F-PEAA) and corresponding fluoro-poly(ether

imide) (6F-PEI) showed their distinct features.

The characteristic absorption bands of amides and carboxyl groups in the spectra at

3240 to 3320cm-1 and 1500 to 1730cm-1 region disappeared and those of imide ring

appeared near 1784cm-1 (asym. C=O stretching), 1728cm-1 (sym. C=O stretching),

1376cm-1 (C-N stretching) 1063cm-1 and 744cm-1 imide (ring deformation). Also the

aryl-ether absorption band around 1250cm-1 for both amic-acid and imide was very

strong indicating stability of the structure and successful conversion of polyether-amic

acid to poly(ether imide).

123

Figure-10 : FT-IR Spectra of [6FDA + m-SED] fluoro-poly(ether amic acid) (6F-PEAA) and corresponding fluoro-poly(ether imide) (6F-PEI) solid polymer 2.5.1.2. Solubility

The solubilities of ULTEM1000 pellet, KaptonH film and precipitated solid

polymers were tested in NMP, THF, DMAc, DMF, methylene chloride and conc. H2SO4.

The visual observations on solubilities of polymers are recorded in Table 6.

The poly(ether imide) polymers based on PMDA and BPDA were insoluble at room

temperature or partially soluble upon heating in the solvent used. Others were soluble in

NMP, THF, DMAc, and DMF, at room temperature and somewhat partially soluble on

heating in methylene chloride. However, all of these polymers were soluble in conc.

H2SO4 except KaptonH, which showed disintegration. All of the solid fluoro-poly(ether

PEA

%T 744.31

1061.07

1250.33

1376.08

1728.1

1784.4

725.29

1258.01

1545.721664.22

1724

Imide RingDeformation

Aryl-EtherStretchingImide

C-NStretchingimide

Sym C=O Stretching Imide

Asym C=O StretchingImide

C-N Bending

Aryl-EtherStretchingPEA

Amide II

Amide

C=O stretching Amide I

[6FDA + m-SED] (6F-PEI)

Wavenumber (cm-1)

C-N Bending

PEI

1500 500 10002000

[6FDA + m-SED] (6F-PEAA)

Fluoro-Poly(ether-imide): [6FDA + m-SED]

124

imide) (6F-PEI) polymers based on 6FDA were soluble in almost all the solvents tested

at room temperature.

Table-6 : Solubilities and solution properties of polyetherimide solids, ULTEM1000 (solid) and KaptonH (film)

POLYMER COMPOSITION

(Diamine) (Dianhydride)

NMP

THF

DMAc

DMF

MeCl2

Conc. H2SO4

(m-SED) PMDA + - - + - + - - + BPDA + - - + + - + 6FDA + + + + + + BTDA + + - + + + - + ODPA + + + + + +

(p-SED) PMDA + - - + - + - - + BPDA + - - + - + - - + 6FDA + + + + + + BTDA - + - - - + ODPA + - + + - +

(BPADE) PMDA + - + - + - - + BPDA + + - + - + - - + 6FDA + + + + + + BTDA + - + - + - - + ODPA + + + + + +

(BDAF) PMDA - - - - - + BPDA + - - + - + - - + 6FDA + + + + - + BTDA +- - + - + - - + ODPA + + + + + +

ULTEM 1000 + + - + - + - - + KaptonH * - - - - - + - **

*: as received KaptonH Film. Solubility tested at 2% solid concentration; + : Soluble at room temperature (25°C); + - : Soluble upon heating (~35°C) - : Insoluble at room temperature (25°C); ** : Polymer disintegrates

2.5.1.3. Viscosity and molecular weights

The inherent viscosities of poly(ether amic acid) and poly(ether imide) were

determined. The molecular weight of poly(ether imide) solid was determined by the gel

permeation chromatography (GPC). These values are reported in Table 7.

The poly(ether-imide)s based on PMDA and BTDA with BDAF were insoluble in

eluent solvent mixture at room temperature, hence their molecular weights could not be

125

Table-7 : Molecular weights determination by gel permeation chromatography (GPC)

Molecular Weights by GPC POLYMER

COMPOSITION (Diamine) (Dianhydride)

PA

Inh.[η] dL/g

PEI

Inh.[η] dL/g Mw Mn d

(Mw/Mn)

(m-SED) PMDA 0.89 0.52 61500 24700 2.49 BPDA 0.59 0.36 40050 17050 2.35 6FDA 0.66 0.49 45480 26750 1.70 BTDA 0.36 0.29 35655 15850 2.25 ODPA 0.62 0.42 94450 52470 1.80

(p-SED) PMDA 0.95 0.68 56000 13000 4.5 BPDA 1.51 0.88 54000 2100 2.60 6FDA 1.40 1.07 140000 79000 1.70 BTDA 1.13 0.81 89000 30000 2.90 ODPA 1.20 0.62 62000 24000 2.70

(BPADE) PMDA 0.75 0.60 86000 11000 7.40 BPDA 1.12 0.80 91900 35350 2.60 6FDA 1.19 0.73 92000 46000 2.00 BTDA 0.88 0.49 56000 22400 2.5 ODPA 0.83 0.66 66000 27000 2.45

(BDAF) PMDA 1.19 INS ND ND ND BPDA 0.74 0.62 72245 30100 2.40 6FDA 0.74 0.64 124500 68611 1.80 BTDA 0.69 INS ND ND ND ODPA 0.81 0.73

ULTEM 1000 NA 0.78 82190 46175 1.78 KaptonH * NA INS ND ND ND

*: as received KaptonH Film. INS : Insoluble at room temperature (25°C) in eluent mixture [THF / DMF (1:1) mixture containing 0.06M LiBr and 0.06M H3P04; NA : Not available; ND : Not determined

determined. Most fluoro-poly(ether imide) (6F-PEI) had high inherent viscosities and

reasonable molecular weights with narrow molecular weight distributions, indicating that

a high degree of polymerization was achieved, which is necessary for achieving a

sufficient level of desired properties of polymer for electronics, and aerospace

applications.

2.5.1.4. Glass transition temperature (Tg)

The Glass transition temperature (Tg) values, and thermal decomposition data are

tabulated in Table 8. The Tg values for solid polymer were on an average 2% lower than

their films. This can be attributed to the fact that chemical imidization method typically

126

reaches 98% conversion rate as compared to thermal imidization. However, this method

is commonly used when solid polymer is needed for polymer transformation by

conventional polymer processing method. Wherein heating is carried out at a slower rate

in controlled condition close to the melt temperature at which 100% conversion to imide

structure is achieved.

Table-8 : Glass transition temperature and 5% thermal stability of poly(ether imide) solids

POLYMER COMPOSITION (Diamine) (Dianhydride)

DSC 1 Tg [°C]

TGA2 5% Wt Loss [°C] in Air

(m-SED) PMDA 267 578 BPDA 240 592 6FDA 241 544 BTDA 222 585 ODPA 215 539

(p-SED) PMDA 363 540 BPDA 284 535 6FDA 289 546 BTDA 274 530 ODPA 265 520

(BPADE) PMDA 312 522 BPDA 249 536 6FDA 248 532 BTDA 239 514 ODPA 224 521

(BDAF) PMDA 322 530 BPDA 256 520 6FDA 266 530 BTDA 257 512 ODPA 245 535

1: (a) 1st heating from 100°C to 425°C @ a rate of 20°C/min.; (b) Cooling from 425°C to 100°C @ a rate of 20°C/min.; (c) 2nd heating from 100°C to 425°C @ a rate of 20°C/min. 2: Heating from 100 to 1000°C @ a rate of 20°C/min

The DSC curves of only (6F-PEI) films is shown in Figure 11. The Tg values, and

other thermal properties including 5% weight decomposition, thermo-oxidative stability

and thermo-mechanical properties of fluoro-poly(ether imide) (6F-PEI) polymer film

samples and ULTEM1000 (solid) and KaptonH (film) are reported in Table 9.

127

Figure-11 : Glass transition temperature (Tg) of fluoro-poly(ether imide) films

127

128

Table-9 : Thermal and thermo-mechanical properties of fluoro-poly(ether imide) polymer films

POLYMER

DSC Tg

[°C]

TGA

5% Wt Loss

[°C] (Air) (N2)

TGA Char Yield [%]

TOS

Weight. Loss [%]

TMA CTE

(mm/°C)

DMA

Storage Modulus

100°C 200°C (MPa)

DMA Tan δ (Max) [°C]

DMA Loss

Modulus E" (Max)

[°C] 6FDA + p-SED

293

544 561

51.6

2.3

6.06 x 10-5

187.4 139.1

294.1

293.3

6FDA+ m-SED

244

540 550

55.0

5.5

9.07 x 10-5

297.1 232.1

244.0

242.0

6FDA+ BPADE

259

527 559

55.9

16.0

8.93 x 10-5

199.4 158.1

260.0

256.3

6FDA + BDAF

266

525 552

52.6

7.0

6.20 x 10-5

147.6 123.1

274.0

265.2

ULTEM1000

218

522 526

48.0

3.0

5.95 x 10-5

179.3 116.5

225.8

223.3

KaptonH

407*

601 603

53.4

4.4

3.15 x 10-5

269.7 214.8

403.0

419.0

* : Measured by TMA of as received Film

The glass transition temperatures (Tg) of all 20 solid polymers were plotted against

dianhydride structure as shown in Figure 12. The wide range in Tg values reflects the

large variation in molecular structures. The plot clearly reflects that the Tg of a polymer

increased with increasing rigidity of the dianhydride structure. Rigidity of the

dianhydride structure can be controlled via the incorporation of various “separator or

spacer” groups, such as -CO-, -O-, -SO2-, -C(CF3)2- [9-10, 75-78]

From the Figure 12 it is important to note that the observed Tg increases based on the

dianhydride structures present in the polymer in the following order in this study (32).

PMDA > BPDA ≥ 6FDA > BTDA > ODPA

There was a significant reduction in Tg of the poly(ether imide) polymers prepared

from meta-oriented 4,4(3-amino phenoxyphenyl) sulfone (m-SED) as compared to 4,4(4-

amino phenoxyphenyl) sulfone (p-SED) isomers. This is due to the distortion of the

linearity of the polyimide chain by meta linked bond angle, thereby reducing rotational

energy [9-10, 75-78].

129

Figure-12 : Glass transition temperature of poly(ether imide)s : Effect of diamine isomers and rigidity of dianhydrides on Tg of polymer

SO

OO NH2NH2

O

SO

OO

NH2NH2

O


C

CH3

OO NH2NH2

CH3


C

CF3

OO NH2NH2

CF3



C

C

O

O

O

C

C

O

O

O

C

C

C

O

O

O

C

O

O

C

O

C C

O

CC

O

O O

OO

C C

C

C

CF3

O O

O

CF3

O

C

O

O

C

O

C C

O

CO

O

O O

O

PMDA BPDA BTDA ODPA6FDA> ≥ > >

200

220

240

260

280

300

320

340

360

380

PMDA BPDA 6FDA BTDA ODPA

DIANHYDRIDES

Tg (o C

)

PEI based on p-SEDPEI based on BDAFPEI based on BPADEPEI based on m-SED

Effect of Diamine Isomers and Rigidity of Dianhydrides on Tg of polymers

SO

OO NH2NH2

O

SO

OO

NH2NH2

O


C

CH3

OO NH2NH2

CH3


C

CF3

OO NH2NH2

CF3



C

C

O

O

O

C

C

O

O

O

C

C

C

O

O

O

C

O

O

C

O

C C

O

CC

O

O O

OO

C C

C

C

CF3

O O

O

CF3

O

C

O

O

C

O

C C

O

CO

O

O O

O


200

220

240

260

280

300

320

340

360

380


DIANHYDRIDES

Tg (o C

)


SO

OO NH2NH2

O

SO

OO

NH2NH2

O


C

CH3

OO NH2NH2

CH3


C

CF3

OO NH2NH2

CF3



C

C

O

O

O

C

C

O

O

O

C

C

C

O

O

O

C

O

O

C

O

C C

O

CC

O

O O

OO

C C

C

C

CF3

O O

O

CF3

O

C

O

O

C

O

C C

O

CO

O

O O

O


C

C

O

O

O

C

C

O

O

O

C

C

C

O

O

O

C

O

O

C

O

C C

O

CC

O

O O

OO

C C

C

C

CF3

O O

O

CF3

O

C

O

O

C

O

C C

O

CO

O

O O

O


200

220

240

260

280

300

320

340

360

380


DIANHYDRIDES

Tg (o C

)


Effect of Diamine Isomers and Rigidity of Dianhydrides on Tg of polymers

129

130

2.5.1.5. Thermal stability and degradation

Evaluating the thermal stability of polymers is important for determining the thermal

performance of polymer at a given upper use temperature limit. Isothermal

thermogravimetric analysis (I-TGA), dynamic thermogravimetric analysis (TGA) and

thermo-oxidative stability (TOS) test are commonly used. Of these three techniques,

dynamic TGA is widely used because it requires small sample and the entire study is

over in few hours.

The 5% weight loss values for solid fluoro-poly(ether imide) polymers by TGA were

on an average 5°C higher than their films. This could be explained by the fact: (1) the

weight of solid sample was higher than film sample; (2) the solid polymers may contain

some residual solvent which would degrade leading to an early carbonization, which in

turn would act as a thermal barrier, and hence a slight increase in 5% wt loss

temperature. However, the 5% weight loss in nitrogen was observed at a temperature on

an average about 21°C higher than in air, which could be explained by the absence of an

oxidizing environment. All polymers showed good thermal stability in such non-

oxidizing atmosphere. The % char yield (residue) in nitrogen was also higher, and in the

range of 52% to 55% at 800°C (Figure 13 through 16).

However, it should be noted here that the 5% weight decomposition (loss) temperature

by TGA does not fully indicate the actual thermal performance of polymer at a given

upper temperature limit.

In plastics industries, a long term service temperature capabilities is one of the

important criteria for a materials to be considered as high performance polymer.

Polyimides are typically known to have such properties. The service temperature is based

upon the ‘Thermal Index’ rating assigned by the Underwriter Laboratories (UL) USA. A

higher UL ‘Thermal Index’ rating for a particular polymer would means that it would

131

Figure-13 : TGA thermogram showing thermal stability (decomposition) air atmosphere

[BTDA + BPADE]

[PMDA + BPADE] [ODPA + BPADE]

[6FDA + BPADE]

[DSPA + BPADE]

[BPDA + BPADE][BTDA + BPADE]

[PMDA + BPADE] [ODPA + BPADE]

[6FDA + BPADE]

[DSPA + BPADE]

[BPDA + BPADE]

131

132

Figure-14 : TGA thermogram showing thermal stability (decomposition) in nitrogen atmosphere

Kapton H

[6FDA + BDAF]

ULTEM1000

[6FDA + p-SED]

[6FDA + m-SED]

[6FDA + BPADE]

Kapton H

[6FDA + BDAF]

ULTEM1000

[6FDA + p-SED]

[6FDA + m-SED]

[6FDA + BPADE]

132

133

Figure-15 : TGA thermogram showing thermal stability (decomposition) in air atmosphere

[6FDA + p-SED]

ULTEM1000

Kapton H

[6FDA + BDAF]

[6FDA + BPADE]

[6FDA + m-SED]

[6FDA + p-SED]

ULTEM1000

Kapton H

[6FDA + BDAF]

[6FDA + BPADE]

[6FDA + m-SED]

133

134

Figure-16 : Thermal degradation of (6F-PEI), ULTEM1000 and KaptonH films by thermogravimetric analysis

100 200 300 400 500 600 700 800 900 10000

10

20

30

40

50

60

70

80

90

100W

eigh

t (%

)

Temperature (°C)

[6FDA+p-SED]

[6FDA+BPADE]

[6FDA+BDAF]

[6FDA+BDAF]

[6FDA+m-SED]

[6FDA+BPADE]

ULTEM1000

KaptonH

ULTEM1000

[6FDA+ p-SED]

[6FDA+m-SED]

KaptonH

AIR

NITROGEN

100 200 300 400 500 600 700 800 900 10000

10

20

30

40

50

60

70

80

90

100

100 200 300 400 500 600 700 800 900 10000

10

20

30

40

50

60

70

80

90

100W

eigh

t (%

)

Temperature (°C)

[6FDA+p-SED]

[6FDA+BPADE]

[6FDA+BDAF]

[6FDA+BDAF]

[6FDA+m-SED]

[6FDA+BPADE]

ULTEM1000

KaptonH

ULTEM1000

[6FDA+ p-SED]

[6FDA+m-SED]

KaptonH

AIR

NITROGEN

134

135

provide a long term thermal performance in terms of good mechanical and dimensional

durability, electrical insulative properties, solvent resistivity, etc at higher temperature.

2.5.1.6. Thermo-oxidative stability (TOS)

To determine the actual thermal performance of any given polymeric materials

according to the ASTM and the Underwriters Laboratories [79], the polymer has to be

tested above its intended continuous use temperature for certain minimum number of

hours. Since, dynamic TGA analysis is over in less than couple of hours, and the 5%

weight loss (decomposition) temperature obtained by TGA analysis does not fully

indicate the long term thermal performance of polymer at a given upper temperature

limits. Therefore, isothermal thermo-oxidative stability (TOS) measurements of only

6FDA based (6F-PEI), such as [6FDA + p-SED], [6FDA + m-SED], [6FDA + BPADE]

Figure-17 : Isothermal heating of (6F-PEI), ULTEM1000 and KaptonH films in air at 315°C (600°F) for 300 Hours

80

85

90

95

100

0 25 100 150 200 250 300

Time (Hours)

% W

eigh

t Ret

aine

d

KAPTON-H[6FDA+p-SED][6FDA+BPADE]ULTEM 1000[6FD+BDAF][6FDA+m-SED]

2.3 3.0 4.4 5.5

7.0 16.0

% Wt. Loss

136

and [6FDA + BDAF] from the series and ULTEM1000 and KaptonH films were

carried out in a programmable oven at 315°C (600°F) for 300 hours in air environment.

The film samples were preheated at 150°C for one hour and their weights at this point

were taken as the reference or 100% weight value. During the test, the crucibles with the

samples were removed from the oven simultaneously at appropriate times, and

immediately sealed for cooling. They were weighed and then returned to the oven

immediately for further aging. Neglecting the initial weight loss of all the samples tested,

which is thought to be associated with the removal of solvent and absorbed moisture, an

approximate weight loss was calculated.

Only 2 to 3% weight loss occurred for [6FDA + p-SED] and ULTEM1000, whereas

4.4% weight loss for KaptonH, 5.5% weight loss for [6FDA + m-SED], and 7% weight

loss for [6FDA + BDAF] and 16% weight loss for [6FDA + BPADE] polymer occurred

over 300 hours. The 97.7% weight retention of [6FDA + p-SED] over 300 hours is the

best observed among the materials tested (Figure 17).

2.5.1.7. Thermo-mechanical properties

The thermo-mechanical properties of (6F-PEI) films, such as storage modulus G', tan

δMax, and loss modulus E" values are also tabulated in Table 9. The peak of tan δMax

was identified as the glass transition temperature, because a large decrease of the storage

modulus G' occurred at that temperature.

While comparing the (6F-PEI) film Tg of 266°C to 293°C measured by DSC with

those of tan δ value of 274°C to 294°C measured by DMA, it was noted that the Tg

values obtained from DMA were slightly higher. The thermo-mechanical properties of

polyimides are directly related to the inter- and intra-molecular chain conformation

rotation flexibility beside the chemical structure [2, 78]. They also depend on the

previous heat history of the polymer samples. The results could be compared with

137

decreasing order of rigidity and stiffness of polymer backbone as indicated by the

varying value of glass transition temperature.

2.5.1.8. Coefficient of thermal expansion (CTE)

The coefficient of thermal expansion (CTE) values of fluoro-polyetherimides were

higher (5.95x10-5 to 9.07x10-5m/m°C) than KaptonH (3.15x10-5m/m°C), but were

consistent with those of flexible polyimides. The rigid rod type polyimides possess very

low CTE value similar to metals. On the other hand, polyetherimides containing flexible

'spacer' links, such as -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -SO2-, and meta substituted

aromatic ring tend to have higher CTE values. In addition, the polyimide film prepared

from its solution generally has a higher CTE value than that from the corresponding

polyamic acid due to its high temperature curing (imidization)/heating history [50, 57].

2.5.1.9. Transparency and color

The fluoro-polyimides are known for their excellent transparency, low moisture

absorption, and low dielectric properties and high thermal stability, which are highly

desirable properties.

The flexible films of such high temperature stable fluoro-polyimides that have high

optical transparency in the 300-600 nm range of the electromagnetic spectrum are

specially useful in aerospace applications, such as antennae, solar cells and thermal

control coating systems.

The films thickness of fluoro-poly(ether imide)s [6FDA + p-SED], [6FDA + m-SED]

and [6FDA + BDAF] were measured by a scientific film thickness measurement

instrument from Starret Precision Instruments, USA, model ST-1-25 having a measuring

range of 1-125mm /or 0.0-12500µm with a resolution of 0.001mm /or 1.25µm and a

measuring accuracy of ± 0.002mm /or ± 2.5µm. The film thickness was determined as

138

the average of 5 readings on each film sample. They were almost identical as reported in

Table 10.

The films of these three fluoro-poly(ether imide)s were colorless with transparency in

the range of 80 to 90% at 500 nm solar wavelength as compared to 72 and 27% for light

amber to amber colored ULTEM1000, and KaptonH films respectively (Figure 18).

Koton et al. [57] explained that the transparency of visible light by polyimide films is

closely associated with the electronic characteristic of the monomer used in the

synthesis.

Figure-18 : % Transparency of fluoro-poly(ether imide) films

200 300 400 5000

20

40

60

80

100

ULTEM1000

[6FDA+BDAF]

KaptonH

[6FDA+BPADE][6FDA+m-SED]

[6FDA+p-SED]

%T

Wavelength (nm)

200 300 400 5000

20

40

60

80

100

200 300 400 5000

20

40

60

80

100

ULTEM1000

[6FDA+BDAF]

KaptonH

[6FDA+BPADE][6FDA+m-SED]

[6FDA+p-SED]

%T

Wavelength (nm)

139

Table -10 : Fluoro-poly(ether imide) polymer film properties

Polyetherimide Film Thickness

[µml]

Film Characteristic*

Transparency [%]

Moisture absorption

[%]

d-Spacing [Å]

6FDA + p-SED* 27.50 Very light brown to colorless flexible film

86.4 0.5 4.72

6FDA+ m-SED* 24.25 Very light brown to colorless flexible film

82.3 0.3 4.56

6FDA+ BPADE* 35.00 Pale yellowish color flexible film

79.1 1.05 5.08

6FDA + BDAF* 27.50 Very light yellow to colorless flexible film

85.5 0.55 5.48

ULTEM1000* 25.00 Light amber color flexible film

72.3 1.52 5.24

KaptonH** 25.00 Amber color flexible film **

27.1 3.0 NA

* : Film prepared from solution of 15% polymer solid concentration in NMP; ** : Film used as received, NA : Not determined Many non-fluorinated polyimides films are known to have yellow to dark amber

colors whereas the fluorinated polyimides films are almost colorless. The optical

transparency to visible light is also affected by the intra- and inter-molecular interaction

of π electrons between the monomer moieties in the polymer chain inducing a charge

transfer complex (CTC). The π electron transfers from the electron donating diamine to

the electron acceptor dianhydride moiety. The polyimide chain is basically composed of

an alternating donor and acceptor moieties, which can interact with each other inducing

inter-chain CTC. It is possible to reduce CTC by incorporating electronegative fluorine

groups on the polymer backbone or incorporating bulky electron withdrawing substituent

groups, as they restrict the inter-chain conformational mobility and thus lower the CTC

[9-10, 57, 80-81].

2.5.1.10. Hydrolytic stability

Moisture absorption and diffusion properties are important with regards to their

practical use in microelectronics and separation membranes. The absorbed water in

polymer structures affects their performance and long term stability [82]. Very

significant lower moisture absorption values were noted for fluoro-poly(ether imide)

140

films at 100 RH at 50°C (Table 10). The values were in the range of 0.3% to 1.05% for

the (6F-PEI) containing hydrophobic -C(CF3)2- groups. These values were lower than

those of non-fluorinated poly(ether imide)s, such as ULTEM1000 (1.52%) and

KaptonH (3.0%) films, which were used as 'controls' in this study. The % absorption

values measured in our study for ULTEM1000 and KaptonH films were found to be

similar to those reported in the product brochures (1.25% at 23°C for 50% RH and 2.9%

at 23°C for 100% RH) respectively [83-85]. The highly transparent polyimides with low

moisture absorption are suitable for wave-guide applications in optoelectronics.

2.5.1.11. Morphology

The X-ray diffraction spectra of the (6F-PEI) solids as shown in Figure-19 were broad

and without any significant or obvious peaks indicating that the polyetherimides were

amorphous. Polymers showed an amorphous pattern in the XRD spectral window range

from 2θ = 5° to 2θ = 35°. The result was consistent with that of the solubility behavior of

polymers and also with the glass transition temperature (DSC) result. This could be

explained in terms of the presence of 'spacer' link such as ether, isopropylidene, and

sulfonyl group. This 'spacer' link reduces the rigidity of the polymer chain which inhibits

its packing [86].

In our study, however, the XRD spectrum of KaptonH film showed no peak in the

scanning region. It is likely that the film sample was not thick enough to get some

meaningful reading. An increase in d-spacing was observed when bulkier group -

C(CF3)2- was substituted for -C(CH3)2- in the structure of the diamine moiety of polymer

chain segment, as shown in the case of fluoro-poly(ether imide) [6FDA + BPADE], the d

spacing was 5.08Å whereas for the fluoro-poly(ether imide) [6FDA + BDAF], the d

spacing was 5.48Å (Table 10).

141

Figure-19 : X-ray diffraction patterns of (6F-PEI) solids, ULTEM1000 and KaptonH films

The increased inhibition of the conformational rotation is also reflected in a slight

increase in Tg values of 6F-PEIs [6FDA + BDAF] with Tg =266°C as compared to

[6FDA + BPADE] with Tg =259°C. The meta oriented monomer also greatly reduces

polymer chain segmental mobility and thus lowers d spacing and Tgs [87-89]. In the case

of [6FDA + p-SED] and [6FDA + m-SED], which are made from para and meta isomers

of 'ether' containing diamine monomer with sulfonyl (-SO2-) spacer group, the d-spacing

and Tg values lowered from 4.72Å to 4.56Å and 293°C to 244°C respectively. The

ULTEM® 1000 (d spacing = 5.24Å and Tg = 218°C) was completely amorphous.

2.5.1.12. Mechanical properties

The mechanical properties of (6F-PEI) films are summarized in Table 11. The films

possessed a tensile strength in the range of 11.5 to 14.0 Kpsi and elongation at break of

6.65 to 14.0% and modulus of 339 to 424 Kpsi. These polymers have comparable tensile

5 10 15 20 25 30 35

100

200

300

400

500

600

700

DIFFRACTION ANGLE (2θ)

[6FDA + p-SED]

Kapton H Film

ULTEM 1000 Film

[6FDA + BDAF]

[6FDA + BPADE]

[6FDA + m-SED]

INTENSITY

142

properties, even when the diamine structures are different. The only exception was that

the % elongation at break values for 'control' samples of ULTEM1000 and KaptonH

films were higher (60% and 72% respectively) than the (6F-PEI) in our study.

Table-11 : Mechanical properties of fluoro-poly(ether imide)s polymers

POLYMER Density1 ρ

(g/cc)

Elongation @ Break (%)

Tensile Strength (Kpsi)

Modulus (Kpsi)

6FDA + p-SED 1.41 14.0 14.00 424 6FDA + m-SED 1.33 13.1 12.70 413 6FDA + BPAD 1.39 10.8 11.50 339 6FDA + BDAF 1.40 6.65 13.30 353 ULTEM10002 1.29 60.0 15.20 430 Kapton H3 1.42 72.0 25.00 430

1: Measured of compression molded plates of 1.5mm thickness; 2 : [Reference # 33], 3: [Reference # 34] 2.5.1.13. Electrical properties

The electrical properties, measured on the dried film samples of two fluoro-poly(ether

imide)s [6FDA + p-SED] and [6FDA + BPADE], and 'control' samples of KaptonH and

ULTEM1000 of thickness ranging from 25 to 35 µm are reported in Table 12. The

dielectric constants at 10 MHz ranged from 2.65 for fluoro-poly(ether imide) [6FDA +

BPADE] of the series to 3.2 for the commercial Dupont’s polyimide KaptonH film.

Overall, the incorporation of fluorine atoms into polymer backbone via trifluoromethyl

group attachment has produced low dielectric properties [11, 23, 29, 41, 58, 76] as

compared to ULTEM1000 and KaptonH, which do not have trifluoromethyl groups in

the polymer backbone.

Table - 12 : Electrical properties of fluoro-poly(ether imide) polymer films

POLYMER

Film Thickness

[µm]

Dielectric Constant

@ 10 MHz 1

Dissipation Factor

@ 10 MHz 2

Volume Resistivity

(Ohm.cm) 3 6FDA + p-SED 27.50 2.74 3.5 x 10-3 1.91 x 1016 6FDA + BPADE 35.00 2.65 3.7 x 10-3 2.09 x 1016 ULTEM1000 25.00 3.10 3.9 x 10-3 6.70 x 1016 KaptonH * 25.00 3.20 1.6 x 10-3 1.66 x 1016

1 : Measured as per ASTM D-150-81 method; 2 : measured as per ASTM D-150-81 method; 3: Measured as per ASTM D-257-78 method; * : Reference 34

143

2.5.1.14. Polymer melt flow viscosity stability

The melt rheology/processing stability of the fluoro-poly(ether imide) solid samples

[6FDA + m-SED], [6FDA + p-SED], [6FDA + BPDAE] and [6FDa + BDAF] were

compared against ULTEM1000 by measuring the complex viscosity as a function of

time [74, 90].

Figure 20 : Complex melt viscosity of poly(ether imide) (6F-PEI)s as a function of time The complex viscosity of the sample plotted as a function of time as shown in Figure-

20, indicates that 6FDA containing fluoro-poly(ether imide) [6FDA + m-SED], [6FDA +

p-SED] and [6FDA + BPDAE] behaved similarly to poly(ether imide) ULTEM1000,

and had stable melt viscosity at 50°C above Tg for 30 minutes. Whereas the melt

viscosity of [6FDA + BDAF] increased by 30% in the given time scale, which may be

due to the onset of molecular weight increase or crosslinking in the melt processing

condition used. However, these values are within manageable processing parameters.

Hence, the poly(ether imide)s (6F-PEI) synthesized for this study could be easily melt

Complex Melt Viscosity as a Function of Time

@ T = Tg + 50 oC

1

10

0 3 6 9 12 15 18 21 24 27 30

Time (min)

Com

plex

Vis

cosi

ty

(Poi

se)

[6FDA + m -SED] ULTEM 1000[6FDA + BPADE] [6FDA + p-SED][6FDA + BDAF]

ω = 1 rad /sec

10

107

Complex Melt Viscosity as a Function of Time@ T = Tg + 50 oC

1

10

0 3 6 9 12 15 18 21 24 27 30

Time (min)

Com

plex

Vis

cosi

ty

(Poi

se)

[6FDA + m -SED] ULTEM 1000[6FDA + BPADE] [6FDA + p-SED][6FDA + BDAF]

ω = 1 rad /sec

10

107

144

processed by any conventional compression molding methods.

2.6. CONCLUSION

A series of high temperature stable poly(ether imide)s have been synthesized by

solution condensation polymerization. The FT-IR study confirmed that polyether-amic

acid was successfully converted to poly(ether imide) by chemical immidization method.

Of these poly(ether imide)s, all of the fluoro-poly(ether imide)s based on 6FDA were

soluble in almost all the organic solvents tested in this study at room temperature. The

films of fluoro-poly(ether imide)s (6F-PEI), such as [6FDa + p-SED], [6FDA + m-SED]

and [6FDA + BDAF] were almost colorless and had transparency in the range of 80 to

90% at 500 nm solar wavelength. Very significant lower moisture absorptions (in the

range of 0.3 to 1.05%) were noted for these films at 100 RH at 50°C. These fluoro-

poly(ether imide) are amorphous as determined from XRD measurements. The fluoro-

poly(ether imide) polymer, [6FDA + p-SED] (d spacing = 4.72Å, and Tg 293°C) had

higher thermo-oxidative stability (TOS) and an exceptionally low dielectric constant

value of 2.74. Its dielectric constant value was significantly lower than those of

ULTEM1000 and KaptonH. The glass transition temperatures (Tg) of all fluoro-

poly(ether imide) synthesized were in excess of 240oC and well above the Tg of

ULTEM1000. However, they could be processed readily into thin film and/or molded

articles via conventional processing technique. It was demonstrated that the glass

transition temperature (Tg) and dielectric constants (ε') of poly(ether imide)s could also

be tailored by controlling the rigidity of the chain through the introduction of rigid or

flexible “separator" groups [81-82, 91]. These fluoro-poly(ether imide)s (6F-PEI) are

ideal candidates for the applications such as high temperature insulators and dielectrics

for micro-electronic packaging, coating and adhesive as well as substrates for electronic

145

flex circuit and matrices for high performance composites for aerospace and advanced

aircraft and materials for gas separation membranes.

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152

CHAPTER - 3

SYNTHESIS AND PROPERTIES OF DESIGNED LOW-K FLUORO-

COPOLY(ETHER IMIDE)S

153

3.1. INTRODUCTION

3.1.1. Research background

Some aromatic polyimides have very important applications in microelectronics since

they possess outstanding thermal, mechanical and electrical properties as well as

excellent chemical resistance [1]. The wide range of applications of these polymers

includes substrate films for flex circuits, interlayer dielectric in integrated circuits,

junction protective coatings, conductive coatings, adhesives, and base materials for

photosensitive formulation for electronics applications, etc. as well as materials for gas

separation membranes. The good dielectric and adhesion properties, mechanical strength

and the increased operating reliability in integrated circuits make their usage very

significant [2-3]. Some polyimides show low relative permittivity, i.e., dielectric

constant, (ε’), low dielectric loss over a wide frequency range and high breakdown

voltage, and therefore are particularly attractive as interlevel dielectrics in integrated

circuits fabrication [4-10]

There are limitations as to which polymers can be used in microchip fabrication. There

are considerable number of critical requirements that new materials must meet.The most

important among them besides low dielectric constant, is to have high thermal stability.

The formation of interconnect line in microchips involves processing temperature well

above the glass transition temperature of many known conventional polyimides. Thus the

multilevel metallization step during the microchip device fabrication requires high

thermal stability of polymeric materials that might be used as interlayer dielectrics.

Besides, thermal stability and dielectric constant, there are other important

requirements to be met before a new polymeric materials could be used as an interlayer

dielectric [11-13], such as, moisture uptake, purity, adhesion to wafer substrate, and low

coefficient of thermal expansion (CTE), since the high temperature processing

154

requirement has already narrowed down to only a few number of polyimide structures,

which can meet the above mentioned criteria for current generation of microchips. As the

pitch size continues to decrease, the microelectronic industry would experience a surge

in further miniaturization of microchip circuitry. Hence, there is a considerable interest in

polymer research to develop new polyimides which would meet the dielectric

requirements. These interlayer dielectric requirements are defined by the SEMATECH

Roadmap prediction [14] for the next 10 years developed by Semiconductor Industry

Association, USA in 1998 as given in Table 1 below.

Tabl-1: 1998 SEMATECH Roadmap prediction for interlayer dielectric for next 10 years [14]

Year Interlayer Pitch Size (nm)

Dielectric Constant Required (ε′)

1995 350 4.1 1998 250 3.0-4.1 2001 180 2.5-4.1 2004 130 2.0-2.5 2007 100 1.5-2.0

Since the compatibility of several polyimides with the semiconductor manufacturing

processes and the reliability of the resulting devices has been proven, to a greater extent,

currently, multilevel chip fabrication industry uses such polyimide material with a

dielectric constant of less than 4 but greater than 3.1 for the fabrication of chips with

interconnect line distance narrowed down to 180 nm [15]. As the minimum device

features shrink below 180 nm, the increase in propagation delay, as well as the crosstalk

and power dissipation of interconnect would become the limiting factors in the ultra-

large scale high speed integration microelectronic device’s performance [16-20].

In microelectronic device circuitry, the propagation velocity of signal is inversely

proportional to the square of the dielectric constant (ε’) of the propagation medium [12].

Therefore, a low dielectric constant is necessary for faster signal propagation in

microelectronics devices without cross talk for newer multilevel high-density and high-

155

speed electronics circuits. A desirable value should be below 3.1 at 1 kHz. Dielectric

constant of commercially available polyimides are typically 3.15 to 3.5. Kapton-H,

[PMDA + 4,4-ODA] has a dielectric constant of 3.5 [21], and Upilex-S [BPDA + p-

PDA] [22] and the poly(ether imide) ULTEM-1000, [BPADA + m-PDA] [23], has

dielectric constant of 3.5 and 3.15 respectively . All the three polyimides showed their

usefulness up to a point when the requirement for further lower dielectric polymeric

material becomes apparent. Besides KaptonH, both UpilexS and UpilexR not only

have higher Tgs (> 400°C), but available only in non-thermoplastic film form. Whereas,

ULTEM1000 is a melt processable poly(ether imide) engineering resin with Tg of

218°C. Also, Kapton, and Upilex are known to have higher moisture absorption (>

3.0), while ULTEM, not only has a lower moisture absorption (> 1.5), but also a lower

continuous use temperature (170°C). Hence these polyimides are now unattractive for

the newer high continuous use temperature advanced microelectronics

fabrication/processing applications.

As we have seen in Chapter 2, fluorination is the most effective means to increase

thermal and hydrolytic stability. Amongst them, bis-trifluoromethyl groups containing

aromatic polyimides are expected to provide critically superior thermal stability for

electronic packaging and an aerospace composite matrix system [24-28]. St Clair et al.

[29-30] have also shown that the incorporation of fluorine-containing monomers

increases the optical transparency in the polyimide polymers. In addition, Haider et al.

[31] have also shown that wholly fluorinated polyimides have lower dielectric constants.

The highest fluorine-containing polyimides from Hoechst Celanese Corp. USA,

SIXEF-33 [6FDA+3,3-6F diamine] and SIXEF-44 [6FDA+4,4-6F diamine] prepared

from 2,2-bis(dicarboxyphenyl) hexafluoropropane dianhydride, (6FDA), and 2,2-bis(4-

aminophenyl) hexafluoropropane, (3,3-6F diamine), 2,2-bis(4-aminophenyl)

156

hexafluoropropane, (4,4-6F diamine), exhibited the lowest dielectric constant (ε′) of 2.58

[32]. However, these hexafluoroisopropylidene group (i.e., -6F groups) containing

wholly fluorinated fully imidized polymers have sufficiently disrupt chain packing,

which enhance their solubility in common organic solvents, but at the same time have

also reduced the moisture absorption due to the non polar character of these

hexafluoroisopropylidene groups. Also, since these (-6F) groups introduce a kind of kink

(twist) into the polymer backbone, and thus providing conformational freedom, these

polymers do not behave like rigid rod-like polymers, but rather exhibit a high

coefficients of thermal expansion (CTE) [15, 31]. Similarly, other wholly fluorinated

poly(ether imide) [6FDA + BDAF] or [6F-BDAF] reported as LARC-CP1 by NASA

was based on 6FDA and 2,2-bis[4-(4-aminophenoxy)diphenyl] hexafluoropropane

(BDAF) [24-28,-32]. This polymer technology was licensed by Ethyl Corp. Baton

Rouge, Louisiana, USA, which later commercialized it in the precursor form, i.e.,

poly(ether amic acid) (PEAA) under trade name of EYMYD, which had a dielectric

constant (ε′) of 2.99 in its fully imidized form [35-37]. For the interlevel dielectrics

application in integrated circuit fabrication, wholly fluorinated polyimides were looked

upon as attractive candidates [4-10, 15]. However, besides, wholly fluorinated

polyimides are either patented or reported in the literature, all the three fully imidized

polyimides were prohibitively expensive. This is because of their extremely high cost of

production due to prohibitively expensive fluorinated diamines as discussed in Chapter

1, section 1.1.3.1. Currently, none of these fluoro-polyimides are available commercially.

It is obvious that to meet the challenges of the microelectronic industry for providing a

suitable polymeric material for fabricating new generation of microchips with

interconnect line distance of 130nm and less, the search for newer polyimides with a

dielectric constant less than 3.1 will continue.

157

3.1.2. Research Objectives

The objective of the present study was to achieve the target polymer properties as

shown in Table 27 in the Chapter 1. Therefore it is the intention of this research work to

synthesize several copolyimides from fluorinated and non-fluorinated monomers and

evaluate their structure property relationship in order to find a good compromise between

low dielectric constant and other desirable properties. Hence the additional objective of

the continuing research work was to synthesize and develop high-performance low-K

fluoro-copoly(ether imide) polymers (6F-CoPEI) based on the previously discussed

commercially available aromatic fluorinated dianhydride and di-ether linkage containing

diamines having sulfone, isopropyl groups, and bis-trifluoromethyl group, to fabricate

their films and characterize their properties, and to study the thermal stability kinetic of

the selected low-K fluoro-copoly(ether imide) polymer films, and to understand the

structure-property relationships with regards to the effect of chemical structure of co-

monomer (diamine) on their thermal stability and electrical properties.

For the dielectric properties, it is surprising to note that only a few papers [38-45] have

been published on the estimation/prediction of dielectric properties for polyimides.

Literature suggests that typically there are two types of polymer behaviors under

electrical field which are of interest [38]. They are:

The polymer behavior at low electric field strengths:

• Dielectric constant [a.k.a Permittivity constant (ε′)]

• Dissipation factor;

These are directly related to the chemical structure of the polymer.

Whereas

The polymer behavior at high electric field strengths:

• Electric discharge

158

• Dielectric breakdown

These may be regarded as the ultimate electrical properties [38]. However, these are

greatly complicated by the additional influences due to the analytical methods, and

experimental condition used for their determination. Only the ‘dielectric constant’ (ε′)

can be estimated by means of the “additive group contribution” method [36]. Therefore

the other objective of this research work was to use “additive group contribution”

method, and to design several new low-k poly(ether imide) polymers and

estimate/predict their dielectric properties. In fact, such exercise of estimation of

dielectric properties would help to:

o design on paper a new and better polymer composition with low dielectric

constant well before actual laboratory synthesis.

o reduce the number of experiments, and carry out actual laboratory synthesis of

only those new polymers (as designed above) whose dielectric constant values

fall within the desired set range.

o predict and understand the relationship between structure and dielectric.

properties of polymers under consideration.

The additional aim of this research was to carry out systematic calculations to derive

and establish the ‘Molar Polarization’ values of conjugated groups such as

‘Phthalimide’ and ‘Pyromellitimide’ groups typically present in non-fluorinated

polyimides, as well as the "Hexafluoroisopropylidene" group present in fluoro-

polyimides structures by additive group contribution method well in advance prior to

polymer design, as these values are very important but not available in literature. The

other aim was to incorporate these values in the empirical mathematical equations

defined by the Lorentz - Lorenz’s theory [46] and the Vogel’s theory [47], and/or if

necessary, develop a new mathematical model (equation) specifically for the estimation

159

of dielectric constant (ε′) of the copolymers, before any attempt is made to design and

synthesize a series of fluoro-copoly(ether imide) polymers in the laboratory. The

dielectric constant (ε′) estimated by such calculation would then be compared and

verified against actual experimentally measured values at 1 kHz at 25°C and the

literature reported values.

After careful consideration, several series of fluoro-copoly(ether imide) compositions

based on di-ether containing diamines, such as 4,4-oxydianiline, 4,4-bis(4-

aminophenoxy) benzene, 4,4-bis(4-aminophenoxy) phenyl sulfone (p-SED), 4,4-bis(4-

aminophenoxy) phenyl propane (BPADE), 2,2-bis[4-(4-aminophenoxy phenyl)]

hexafluoropropane (BDAF), etc., and 2,2-bis(3-4-dicarboxyphenyl) hexafluoropropane

dianhydride (6FDA) were designed on paper, and their dielectric constant (ε′) values

were first estimated by means of mathematical equations defined by the Lorentz -

Lorenz’s theory [46], the Vogel’s theory [47] and Vora-Wang equations [48].

After an extensive exercise of dielectric constant estimation calculation on paper, only

two series of selected co-poly(ether imide) polymers having low dielectric constant

values (by estimation) were actually synthesized in the laboratory using a simplified

solution polymerization process described in Chapter 1 from the commercially available

monomers. Their films were fabricated and characterized for their thermal, electrical

properties. Their thermo-oxidative and hydrolytic stability were studied to understand

structure-property relationships. The effect of chemical structure of co-monomer

(diamine) on their thermal degradation kinetics was also studied through the use of Coats

and Redfern equation. The activation energies for their thermal degradation were

calculated, and the overall thermal stability was compared with thermo-oxidative

stability values. Their glass transition (Tg) was predicted from the Fox equation [49] and

160

compared with experimental results. The estimated dielectric constant (ε’) values for the

both series of fluoro-poly(ether imide)s were compared with experimentally determined

as well as literature values. The results are discussed here.

3.2. EXPERIMENTAL

3.2.1 Materials

Electronic grade 1,2,4,5-benzenetetracarboxylic anhydride, i.e., pyromellitic

dianhydride (PMDA), 2,2-bis(3,4-dicarboxyphenyl)hexafluropropane dianhydride

(6FDA), 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA), 3,3,4,4-

benzophenonetetracarboxylic dianhydride (BTDA), 3,3,4,4-oxydiphthalic anhydride

(ODPA), 2,2-bis[4-(4-aminophenoxy)diphenyl] hexafluoropropane (BDAF), 3,3-

oxydianiline (3,3-ODA), and 4,4-oxydianiline (4,4-ODA), were received from Chriskev

& Co., Leawood, KS, USA; 4,4’-bis(3-aminophenoxy)diphenyl sulfone (m-SED), 4,4’-

bis(4-aminophenoxy)diphenyl sulfone (p-SED), 2,2-bis[4-(4-aminophenoxy) phenyl]

propane (BPADE) were received from Wakayama Seika Kogyo Co. Ltd., Japan;.

2,3,5,6-tetramethyl-1-4-phenylenediamine (Durene diamine), 2,2-dimethyl-4,4’-

diaminobiphenyl (m-Tolidine), 1,3-phenylenediamine (m-PDA) and 1,4-

phenylenediamine (p-PDA), N-methyl pyrrolidone (NMP), tetrahydrofuran (THF), N,N-

dimethylacetamide (DMAc), N,N-dimethyformamide (DMF), methylene chloride, β-

picoline, acetic anhydride, methanol, con. sulfuric acid and phosphorous pentoxide

(P2O5), FT-IR grade KBr, were received from Sigma–Aldrich, USA. All solvents, except

NMP were used as received. The melting points of dianhydride were checked by

differential scanning calorimetry (DSC) and they were found to have sharp melting

points (Table 1). No attempt was made to purify them. ULTEM1000 pellets were

obtained from General Electric, Corp. NY, USA and its films were prepared by solution

casting in lab. KaptonH and UPILEX-S films (25µm thickness) were obtained from E.

161

I. DuPont & Co. DE, USA, and Ube Industries, Japan, respectively. NMP was always

freshly distilled over P2O5 under reduced pressure and stored over pre-dried molecular

sieves and used when needed. Chemical structures of monomers are given in Figure 1.

OO NH2NH2

C

CH3

OO NH2NH2

C

CF3

OO NH2NH2

OSO

CH3

2,2'-Bis[4-(4-aminophenoxy) diphenyl] propane [BPADE]

CF3

2,2'-Bis[4 (4-aminophenoxy) diphenyl] hexafluoropropane [BDAF]

4,4'-Bis (4-aminophenoxy) diphenyl sulfone [p-SED]

C C

C

C

CF3

O O

O

OC

O

CF3

O

6FDA

Figure-1: Structure of monomers

3.2.2 Polymerization

Several methods for the preparation of polyimides have been reported in the literature

[50-60]. The most common procedure used in this investigation was a simplified two-

step polymerization synthesis process [61], which was discussed at length in Chapter 2

(section 2.2.2.1.A). Three fluoro-poly(ether imide)s (6F-PEI), and two series of fluoro-

copoly(ether imide)s (6F-CoPEI) were synthesized as per the respective synthesis

schemes given in Figures 2 and 3.

There are quite a few polyimides and copolyimides cited in various books and

literature [62-79], but none were available commercially. Hence, two non-fluorinated

polyimides (PI), five fluoro-polyimides (6F-PI), and three fluoro-copolyimides (6F-

CoPI) of interest were selected and synthesized as per the respective synthesis schemes

given in Figures 4 and 5. Their dielectric properties, i.e. dielectric constants were

measured and compared with the experimentally determined values and with the

dielectric constants values of above mentioned fluoro-poly(ether imide)s (6F-PEI) and

162

fluoro-copoly(ether imide)s (6F-CoPEI) as well as their literature cited values (if

available).

3.2.2.1. Synthesis of fluorinated poly(ether imide)s

Three fluoro-poly(ether imide) polymers were synthesized from the monomer as

shown in Figure 1 above. The detail of synthesis procedure is discussed in Chapter 2.

3.2.2.1.1. Synthesis of fluoro-poly(ether imide) (6F-PEI) polymers:

Using the polymerization method described in Chapter 2, the following three fluoro-

poly(ether imide)s (6F-PEI) were synthesized at 0.02 mole size scale, as per the reaction

scheme in Figure 2:

3.2.2.1.1.A. Synthesis of [6FDA + p-SED] fluoro-poly(ether imide)s polymer

The fluoro-poly(ether imide)s [6FDA + p-SED], based on 2,2-bis (3,4-

dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and 4,4-bis (3-aminophenoxy)

diphenyl sulfone (p-SED) was synthesized using the reaction scheme given in Figure 2.

The monomer and chemical materials used and their quantities employed are given in

(Table 2).

OC C

CCF3

O

O

O

C C

CCF3

O

O

OH

C C

CCF3

O

O

N

+

n

n

[6FDA + p-SED] Fluoro-poly(ether amic acid) (6F-PEAA)


POLYMERIZATION

6FDA p-SED (Di-ether linked diamine)



[6FDA + p-SED] Fluoro-poly(ether imide) (6F-PEI) polymer

CF3

CF3

CF3

C

C

O

O

N

C

C

O

O

O

C

C

O

O

HO

HN

HN

S OH2N NH2

O S O

O S O

O

O

O

O

O

O

Figure-2 : Polymerization reaction scheme for [6FDA + p-SED] fluoro-poly(ether imide)

163

3.2.2.1.1.A.1 Synthesis procedure

In the case of synthesis of a fluoro-poly(ether imide) [6FDA + p-SED], based on 2,2-

bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 4,4-bis(4-amino-

phenoxy) diphenyl sulfone (p-SED), accurately weighed 8.884g (0.02mole) of solid

6FDA was added to an equimolar amount of diamine (8.65g) pre-dissolved in freshly

distilled NMP to make 20% solid concentration. The reaction mixture was stirred under a

nitrogen atmosphere at room temperature for over 8 hours to make viscous fluoro-

poly(ether amic acid) (6F-PEAA) solution. A 5mL sample of the poly(ether amic acid)

was retained for analysis purpose, and the balance of (6F-PEAA) was then imidized to

form fluoro-poly(ether imide) (6F-PEI).

Table-2 : Monomers and chemicals used for the synthesis of [6FDA + p-SED]

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.884 p-SED 432.50 100 0.02 8.65 NMP (@ 20 % solid NV) 70.14 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.024 2.45 Methanol 2000mL

3.2.2.1.A.2 Chemical imidization procedure

As discussed in Chapter 2, the cyclization can be achieved by either thermal or

chemical means. Thermal imidization process step is not feasible to convert bulk of the

poly(ether amic acid) in a reactor flask. Besides, the process is only good for converting

wet poly(amic acid) film in to a solid polyimide film, and which requires gradual heating

of wet film to a very high temperature (>300°C) in a pre-programmed stepwise heating

cycle over a period of time. Therefore in this experimental study, the chemical

imidization was employed, in which the amic acid was converted to polyimide by a

condensation reaction with the continuous removal of water (a bi-product of

condensation reaction). The reaction was carried out by addition of stoichiometric

amounts of base β-picoline (catalyst) base (pKa 5.6) and a slightly excess of acetic

164

anhydride (dehydrating agent) [80] given in Table 2. The excess acetic anhydride was to

facilitate maintenance of an anhydrous condition throughout the reaction as shown in

reaction mechanism scheme given in Figure 2, and also in Chapter 2. Under flowing

nitrogen environment at room temperature, 3.725g (0.04mole) of β-picoline (pKa 5.6)

was charged to the fluoro-poly(ether amic acid) and stirred for 15 minutes to allow

uniform mixing. Then 2.45g (0.024mole) of acetic anhydride (~20% extra) was added

drop-wise to the reaction mixture over a period of 10 minutes. Then the reaction mixture

was stirred under nitrogen at room temperature for another 8 hours to get fluoro-

poly(ether imide) polymer solution mixture. Small samples of the 6F-PEAA and

imidized polymer 6F-PEI were then precipitated with copious amount of de-ionized

water methanol respectively, and dried at 100oC overnight in an air circulating oven.

Polymer was stored in a desiccator for later analysis, film fabrication and

characterization.

SO

O

OOC

C

C

C

CF3

O O

O

N

C

O

CF3

N

n

[6FDA + p-SED] Fluoro-poly(ether imide) (6F-PEI)

Similarly, the other two fluoro-poly(ether imide)s (6F-PEI) were synthesized as given in Appendix-A. 3.2.2.2. Synthesis of fluorinated copoly(ether imide) polymers

Two series of random fluoro-copoly(ether imide) [6FDA + (n Mole) p-SED + (m

Mole) Di-ether diamine monomer] (6F-PEI) were synthesized by reacting equimolar

amount of 2,2-bis (3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) with a

mixture diether diamines, such as, a mixture of 4,4-bis(3-aminophenoxy) diphenyl

sulfone (p-SED) and 2,2-bis[4-(4-aminophenoxy) phenyl] propane (BPADE), or a

mixture of 4,4-bis(3-aminophenoxy) diphenyl sulfone (p-SED) and 2,2'bis[4-(4-

aminophenoxy) diphenyl] hexafluoropropane (BDAF). In all the cases, the total sum of

165

the number of mole of diamines in the mixture was maintained equal to the number of

mole 6FDA used.

3.2.2.2.1.Synthesis of fluoro-copoly(ether imide) (6F-CoPEI) polymers

The synthesis reaction scheme is given in Figure 3.

3.2.2.2.1.A. Series 1:Synthesis of [6FDA + (n Mole%) p-SED + (m Mole%) BPADE] fluoro-copoly(ether imide) polymer

In this series, three random copolymers were synthesized, by reacting a mixture of p-

SED and BPADE diamine with equimolar weight of 6FDA. The mole ratio of BPADE in

the diamine mixture was increased in an increment of 25% at the same time mole ratio of

p-SED was reduced equally by an increment of 25%. The diamine mixtures respectively

used were as follows: (75 mole% p-SED + 25 mole% BPADE), (50 mole% p-SED + 50

mole% BPADE) and (25 mole% p-SED + 75 mole % BPADE).

S OONH2NH2

Where Y = -C(CH3)2-, - C(CF3)2-

n

Fluoro-Copoly(ether amic acid)

5 to 30% NV, NMPRT

6FDA Di-ether Linked Diamine

Base Catalyst / Acetic AnhydrideRT (- 2H2O)IMIDIZATION

Fluoro-Copoly(ether imide) Polymer

C C

C

C

CF3

O O

O

O

CF3

+ Y OONH2NH2+

n Mole %

O

O

C C

C

C

CF3

O O

O

HNC

O

CF3

S OO

O

O

OHHN

C C

C

C

CF3

O O

O

HNC

O

CF3 OHHN

HO

Y OO m

CC

C

C

CF3

O O

O

NNC

O

CF3

Y OOSO

O

OCC

C

C

CF3

O O

O

N

CF3

n

O

m

pSEDm Mole %

( n + m =1)

HO

CO

N

COPOLYMERIZATION

CO

O

1 Mole

Figure-3 : Synthesis reaction scheme for [6FDA + (n Mole) p-SED + (m Mole) Di-ether diamine] fluoro-copoly(ether imide) 3.2.2.2.1.A.1. Synthesis of [6FDA + (75%) p-SED + (25%) BPADE] fluoro-

copoly(ether imide) polymer A random fluoro-copoly(ether imide) [6FDA + (75%) p-SED + (25%) BPADE], based

166

on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and a mixture of

4,4- bis(3-aminophenoxy) diphenyl sulfone (p-SED) and 2,2-bis[4-(4-aminophenoxy)

phenyl] propane (BPADE) was synthesized as per the above reaction scheme.

3.2.2.2.1.A.1.1. Synthesis procedure

3.2.2.2.1.A.1.1.a. Step-1: Polymerization

Accurately weighed 8.884g (0.02mole) of solid 6FDA was added to an equimolar

amount of diamines mixture [consisting of 6.4875g of p-SED (0.015M) and 2.0526g of

BPADE (0.005mole)] pre-dissolved in freshly distilled NMP to make 20% solid

concentrations. The reaction mixture was stirred under nitrogen atmosphere at room

temperature for over 8 hours to make a viscous random fluoro-copoly(ether amic acid)

(6F-CoPEAA) solution, which was then imidized to form fluoro-poly(ether imide) (6F-

CoPEI). A 5mL sample of the 6F-CoPEAA was retained for analysis purpose, and the

balance was then imidized to form 6F-CoPEI.

3.2.2.2.1 A.1.1.b. Step-2: Chemical imidization

The 6F-CoPEAA was converted to 6F-CoPEI by means of chemical imidization

procedure as discussed earlier. Under nitrogen environment at room temperature, 3.725g

(0.04mole) of β-Picoline (pKa 5.6) was charged to the poly(amic acid) and stirred for 15

minutes to allow uniform mixing. Then 2.45g (0.024M) of acetic anhydride (~20% extra)

was added drop-wise to the reaction mixture over a period of 10 minutes. Then the

reaction mixture was stirred under nitrogen at room temperature for another 8 hours to

get poly(ether imide) polymer solution mixture. Small samples of the 6F-PEAA and all

6F-PEI were then precipitated with 2000mL of methanol and copious amount of de-

ionized water respectively, and dried at 100oC overnight in an air circulating oven. The

6F-CoPEAA and 6F-CoPEI polymers were stored in desiccators prior to characterization

and film fabrication.

167

C C

C

C

CF3

O O

O

NNCO

CF3

Fluoro-copoly(ether imide): [ 6FDA + (75 %) p-SED + (25 %) BPADE] (6F-CoPEI)

0.75

C

CH3

OO

CH3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.25

O

Synthesis information of other two Co-PEIs of this series is given in Appendix A,

section A-3.2.1.

3.2.2.2.1.B. Series 2: Synthesis of [6FDA + (n Mole%) p-SED + (m Mole%) BDAF] fluoro-copoly(ether imide) polymer

Similar to copoly(ether imide)s mentioned in section 3.2.2.2.1.A, in this series three

random copolymers were synthesized, in which the mole ratio of BDAF was adjusted in

an increment of 25% in the diamine mixture. The diamine mixtures used were as

follows: (75 mole % p-SED + 25 mole% BDAF), (50 mole% p-SED + 50 mole%

BDAF) and (25 mole% p-SED + 75 mole% BDAF) respectively.

3.2.2.2.1.B.1. Synthesis of [6FDA + (75%) p-SED + (25%) BDAF] fluoro- copoly(ether imide) Polymer

In the case of synthesis of fluoro-poly(ether imide) [6FDA + (75%) p-SED + (25%)

BDAF] which is based on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride

(6FDA) and a mixture of 4,4-bis(3-aminophenoxy) diphenyl sulfone (p-SED) and 2,2-bis

[4-(4-aminophenoxy) diphenyl] hexafluoropropane (BDAF), the above procedure was

repeated with the following materials and quantities (Table 3) employed.

Table-3 : Monomers and chemicals used for the synthesis of [6FDA + (75%) p-SED + (25%) BDAF]

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.8840 p-SED 432.5 75 0.015 6.4875 BDAF 518.463 25 0.005 2.5923 NMP (@ 20 % solid NV) 71.8553 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000mL

168

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.75

C C

C

C

CF3

O O

O

NNCO

CF3

C

CF3

OO

CF30.25

Fluoro-copoly(ether imide): [ 6FDA + (75%) p-SED + (25%) BDAF] (6F-CoPEI)

O

Synthesis information of other two Co-PEIs of this series is given in Appendix A, section

A-3.2.2.

3.2.2.3. Synthesis of non-fluorinated polyimides (PI)

Two non-fluorinated polyimides were synthesized from the monomers shown in

Figure 4. The detailed synthesis procedure is discussed in Chapter 2. The polymerization

reaction scheme is given in Figure 5.

3.2.2.3.A. Synthesis procedure

3.2.2.3.A.1. Synthesis of poly(amic acid) (PAA)

It is the experience of this author [81-82] that there are several polyimide structures

which due to their insolubility in dipolar aprotic solvents, precipitate out as solid powder

during chemical imidization reaction. These powder polymers can not be transformed

into any useful form for electronics, aerospace, etc. applications. Hence, in such cases,

their precursors, i.e., poly(amic acid) solutions must be used in the fabrication of useful

forms. Thermal imidization poly(amic acid) is the only way to convert into polyimide

structures, such is the case of Kapton H film, which is commercially made from its

(PMDA + 4,4-ODA) poly(amic acid) solution by Dupont [81].

C

C C

C

O O

O

O

O

O

O

NH3

C

C C

CO

O

O

O

O

O

O

CH3

H3C

NH2

ODPA

H2N

m-Tolidine]

H3N

3,3'-ODA

PMDA

C

C C

C

O

O

O

O

O

O

BPDA

H3N NH2

m-PDA

Figure-4 : Chemical structure of monomer for non-fluorinated polyimides

169

3.2.2.3.1. Synthesis of [ODPA + m-Tolidine] poly(amic acid) (PAA)

For the synthesis of [ODPA + m-tolidine] poly(amic acid) based on 3,3,4,4-

oxydiphthalic anhydride (ODPA) and 2,2-dimethyl-4,4-diaminobiphenyl (m-tolidine), an

equimolar amount 17.768g (0.04mole) of ODPA was charged under nitrogen atmosphere

to a pre-dissolved 8.492g (0.04mole) of m-tolidine in freshly distilled NMP to make 20%

solid concentration [Table 4] in 250mL round bottom three-neck flask fitted with

electrical stirrer, addition flask and nitrogen blanket under continuing stirring.

Z OO


, etc.

AC

OCC

OC

O O

O O

Where A = OR X


Aromatic Dianhydride (1 Mol)

H2N A1 NH2+

AC

OHCCHO

C

O O

O O

HN A1

HN

AC

CC

C

O O

O O

N A1N

n

n

POLYMERIZATION20% NV,NMPRT

Aromatic Diamine (1 Mol)

Z OO

Where Y = Single bond, -CH2-, -O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

, etc.

Where A1 = OR Y

-Si(CH3)2-O-Si(CH3)2-,Where Z = X

Where Z = Y

POLYIMIDE

THERMAL IMIDIZATION

POLY (AMIC ACID)

CH3H3C

H3C CH3

CH3

H3C

OR

-2H2O & NMP

Figure-5 : Scheme of polyimide (PI) synthesis via thermal imidization step

The reaction mixture was further stirred under nitrogen atmosphere and its

temperature maintained in between 15 to 20°C for over 8 hours to make viscous

poly(amic acid). The poly(amic acid) was filtered and packaged in polypropylene bottle

under argon blanket and stored in a refrigerator at 5°C.

Table-4 : Monomers and chemicals used for the synthesis of [ODPA + m-Tolidine]

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) ODPA 310.20 100 0.04 17.768 m-Tolidine 212.30 100 0.04 8.492 NMP (@ 20 % solid NV) 105.04

170

C

C C

CO

O

O

N

O

O

N

CH3

H3Cn

[ODPA + m-Tolidine] Polyimide

Similarly, the other two non-fluorinated polyimides (PI) were synthesized as given in

Appendix-A, section A-3.3.1.

3.2.2.4. Synthesis of fluoro-polyimide (6F-PI)

Fluorinated polyimides were synthesized from the monomers shown in Figure 6. The

detailed synthesis procedure is discussed in Chapter 2. The polymerization scheme is

given in Figure 7.

NH2C

C C

C

O

O

O

C

CF3

CF3

O

O

O

NH2

6FDA

H2NH2N

H2N NH2

CH3

CH3H3C

H3C

H2N O NH2

4,4'-ODA

p-PDA m-PDA]

H2N C

CF3

CF3

NH2

4,4'-6F-Diamine 1,4-Diamino Durene

Figure-6 : Structure of monomer used for synthesis of fluorinated polyimides

NH2 R

5 to 30% NV, NMPRT

6FDA

-2H2O & NMPIMIDIZATION

Fluoro-polyimide Polymer [6F-PI]

CC

C

C

CF3

O O

O

OC

CF3

+

n Mole %

CC

C

C

CF3

O O

O

HN

C

O

CF3OH

RHN

CC

C

C

CF3

O O

O

NC

CF3

n

Aromatic Diamine

POLYMERIZATION

HO

n Mole %O

Y OO

X Where X = Single bond, -CH2-, -O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

etc.

Where R = OR


Where Z = Y

NH2

R

n

Fluoro-poly(amic acid) [6F-PAA]

O

N

O

CH3H3C

H3C CH3

OR

CH3

H3C

Figure-7 : Fluoro-polyimide [6F-PI] synthesis scheme

171

The following fluoro-polyimides were synthesized for the purpose of comparing their

dielectric properties. Their solution and thermal properties were also measured and

reported.

3.2.2.4.1. Synthesis of [6FDA + m-PDA] fluoro-polyimide polymer

Fluoro-polyimide [6FDA + m-PDA] based on 2,2-bis(3,4-dicarboxyphenyl)

hexafluropropane dianhydride (6FDA) and 1,3-phenylenediamine (m-PDA) was

synthesized using the above procedure and the following materials and quantities (Table

5) employed.

Table-5 : Monomers and chemicals used for the synthesis of [6FDA + m-PDA]

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FPA 444.20 100 0.12 53.304 m-PDA 108.143 100 0.12 12.98 NMP (@ 20 % solid NV) 265.136 β-Picoline 93.13 0.48 44.70 Acetic Anhydride (~10% extra) 102.09 0.264 26.952 Methanol 12,000

C

C C

CO

N

O

CCF3

CF3

O

N

O

n

[6FDA + m-PDA] Fluoro-polyimide

Similarly, the other four fluoro-polyimides (6F-PI) were synthesized as given in

Appendix-A. section A-3.3.2.

3.2.2.5. Synthesis of fluoro-copolyimide [6F-CoPI]

Three fluoro-copolyimide were also synthesized as per the synthesis scheme given in

Figure 8 for the purpose of dielectric properties comparison only.

3.2.2.5.1. Synthesis of [6FDA + (50%) m-PDA + (50%) p-PDA] fluoro- copolyimide polymer

Fluoro-copolyimide [6FDA + 50% m-PDA + 50% p-PDA] based on 2,2-bis (3,4-

dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and a mixture of 50 mole % of

1,3-phenylenediamine (m-PDA) and 50 mole % of 1,4-phenylenediamine (p-PDA) was

172

synthesized using the above procedure and the following materials and quantities (Table

6) employed.

NH2 A

5 to 30% NV, NMPRT

6FDA


Fluoro-copolyimide Polymer [6F-CoPI]

CC

C

C

CF3

O O

O

OC

CF3

+

(m1 Mole %)

CC

C

C

CF3

O O

O

HN

C

O

CF3OH

AHN

Aromatic Diamine

POLYMERIZATION

HO

(n Mole %)O

Y OO

X


, etc.

Where A = OR


Where Z = Y

NH2

m1

Fluoro-copoly(amic acid) [6F-CoPAA]

O NH2 B

(m2 Mole %)Aromatic Diamine

NH2+

[ m1 + m2 = n ]

CC

C

C

CF3

O O

O

HN

C

O

CF3OH

BHN

HO

m2

CC

C

C

CF3

O O

O

NC

O

CF3

AN CC

C

C

CF3

O O

O

NC

O

CF3

BN

m1m2

Y OO

X


, etc.

Where B = OR


Where Z = Y

CH3H3C

H3C CH3

OR

Figure-8 : Fluoro-copolyimide synthesis scheme

Table-6 : Monomers and chemicals used for the synthesis of [6FDA + 50% m-PDA + 50% p-PDA]

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.04 17.768 m-PDA 108.143 50 0.02 2.1629 p-PDA 108.143 50 0.02 2.1629 NMP (@ 20 % solid NV) 88.368 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.901 Methanol 4000mL

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

5050

Fluoro-copolyimide [6FDA + (50%) p-PDA + (50%) m-PDA] (6F-COPI)

173

Similarly, the other two fluoro-copolyimides (6F-CoPI) of this series were synthesized

as given in Appendix-A, section A-3.3.3.

3.3. FABRICATION

The film fabrication procedure given in Chapter 2 was used, and several polymer films

were prepared.

3.3.1. Polymer film preparation

Except for poly(amic-acid)s [PMDA + 3,3-ODA] and [ ODPA + m-Tolidine], selected

fluoro-poly(ether imide)s (6F-PEI), fluoro-copoly(ether imide)s (6F-CoPEI), fluoro-

polyimides (6F-PI), fluoro-copolyimides (6F-CoPI) and ULTEM1000 solid were

dissolved in NMP to get solutions at 15% solid concentration level. These solutions were

filtered through a 0.5µm filter under nitrogen pressure. The poly(amic-acid)s and filtered

clear solutions were then coated onto glass plates using a doctor blade (Gardner Film

Casting Knife, model AG-4300, Pacific Scientific, USA) with adjustable gate clearance

controlled with micrometer from 0 to 6250µm gap, to obtain uniform thin wet films.

Additionally one higher wet thickness film for [PMDA + 3,3-ODA] was also coated onto

a separate glass plate. The films were dried in a nitrogen environment, then heated

gradually using a stepwise regular intervals heating cycles as described in Chapter 2,

section 2.3.1, in a programmable oven from room temperature up to 250oC, and then

held at 300oC for 1 hour. The heating was shut down and the films were allowed to cool

down gradually to room temperature. Almost colorless to very light yellow to amber

color self-supporting flexible films free of bubbles and pinholes with homogeneous

general thickness ranging from 25 to 37.5µm and thicker (55µm) sample of [PMDA +

3,3,-ODA] films were lifted up from the glass plate by soaking in water for 5 to 10

minutes, and dried with a paper towel and further dried in an oven at 150oC for 30

minutes. Film thickness was measured by Electronic Digimatic Thickness Gage (model

174

547-400) from Mitutoya (Japan) having a measuring range of 1-125mm /or 0-12500µm

with a resolution of 0.001mm /or 1.25µm, and a measuring accuracy of ± 0.002mm /or ±

2.5µm. The film thickness was determined as the average of 5 readings on each film

sample. The as received films of KaptonH, and UPILEXS (25µm thick) and

ULTEM1000 (25µm) were used as 'the control'. Before the characterization was

performed, the films were re-dried in the vacuum oven overnight at 80oC to remove any

moisture absorbed in the film, and then put into the desiccator.


Most methodologies of characterization techniques used in this work were discussed

in the respective sections of Chapters 1 and 2.


Inherent viscosity of fluoro-poly(ether amic acid), (6F-PEAA), fluoro-copoly(ether

amic acid) (6F-CoPEAA), fluoro-poly(amic acid) (6F-PAA), fluoro-copoly(amic acid)s

(6F-CoPAA), poly(amic acid)s (PAA), fluoro-poly(ether imide)s (6F-PEI), fluoro-

copoly(ether imide)s (6F-CoPEI), fluoro-polyimides (6F-PI) and fluoro-copolyimides

(6F-CoPI) were measured using Scott-Gerate Viscometer..

3.4.2. Fourier transform-IR spectroscopy (FT-IR) FT-IR spectra of the fluoro poly(ether amic acid) (6F-PEAA), fluoro-copoly(ether

amic acid) (6F-CoPEAA), fluoro-poly(ether imide) (6F-PEI), and fluoro-copoly(ether

imide) (6F-CoPEI) solids were obtained using Perkin-Elmer FTIR..

3.4.3. Gel permeation chromatography (GPC) Molecular weights of (6F-PEI) and (6F-CoPEI) (6F-PI) and (6F-CoPI) solids and

ULTEM1000 pellet samples were determined. using a Waters GPC system.

3.3.4. Solubility of polymer solids Solubility of sample of (6F-PEI) and (6F-CoPEI) solids, ULTEM1000 pellets and

175

KaptonH film was determined by placing 0.2 g solid polymer or film sample in a small

capped vials containing 9.98 g solvent. The mixture was stirred vigorously with

magnetic stirrer bars at room temperature. The level of solubility was evaluated after 24

hrs. For those insoluble polymers, the mixture was further stirred at a slightly warm

(~35-40°C) temperature for 1 additional hour.

3.4.5. Hydrolytic stability The % moisture absorption measurements of thin films samples of 6F-PEI) and (6F-

CoPEI), and ULTEM1000 and KaptonH films were determined.

3.4.6. Differential scanning calorimetry (DSC) Glass transition temperatures (Tg) of 6F-PEI) and (6F-CoPEI), (6F-PI), (6F-CoPI),

(PI) and ULTEM1000 and KaptonH films were determined from the second heating

cycle using a differential scanning calorimeter (DSC).

3.4.7. Thermogravimetric analysis (TGA) Thermal decomposition temperatures (5% wt. loss) of (6F-PEI), (6F-CoPEI) (6F-PI),

(6F-CoPI), (PI) polymers films, and ULTEM1000 and KaptonH films were

determined using dynamic TGA.


Long-term isothermal, thermo-oxidative stability (TOS) studies of 6F-PEI) and (6F-

CoPEI) films and ULTEM1000 and KaptonH film samples were performed in air for

300 hours at 315oC (600oF) in a Lenton programmable forced air oven with Eurotherm

2408 Temperature controller/programmer from Lenton Thermal Design, UK.

3.4.9. Dynamic mechanical analysis (DMA) β-Relaxation, storage modulus G', and loss modulus E" of (6F-PEI) and (6F- CoPEI)

polymer film samples, and ULTEM1000 and KaptonH films were determined by

Dynamic Mechanical Analyzer (DMA).

176

3.4.10. X-ray diffraction (XRD) The wide-angle X-ray diffraction (WAXD) measurement of the compressed disks of

solid (6F-PEI) and (6F-CoPEI) polymers with an average thickness of 1mm were carried

out on an X-ray diffraction unit (Phillips model PW 1729-10) fitted with Cu - Kα

radiation (30 kV, 20 mA) with wavelength λ of 1.54Å. The scanning rate was 0.5°/min at

ambient temperature. The spectral window ranged from 2θ = 10° to 2θ = 50°. Using the

Bragg equation, (d = λ/2 sinθ), the corresponding d-spacing value was calculated from

the diffraction peak maxima.

3.4.11. Dielectric analysis (DEA) For dielectric constant (ε') measurement of the lab synthesized (6F-PEI), (6F-CoPEI),

(6F-PI). (6F-CoPI), (PI) polymer’s films, and ULTEM1000 and commercial UpilexS,

films were measured between the parallel plats of Dielectric Analyzer (DEA) at a

frequency of 1 and 1000Hz (1kHz) and at 50% relative humidity at temperature of 25°C

in a flowing nitrogen atmosphere condition.

3.5. RESULTS AND DISCUSSION 3.5.1. Properties The properties of polyimide (PI), fluoro-polyimide (6F-PI), fluoro-copolyimide (6F-CoPI),

fluoro-poly(ether imide) (6F-PEI), and fluoro-copoly(ether imide) (6F-CoPEI), and

UPILEXS, ULTEM1000 and KaptonH are listed in Tables 7 through 19.

3.5.2. Polymer’s chemical structural characteristics

The FT-IR spectra shown in Figure 9 clearly indicate the formation of peak associated

with imide ring and disappearance of the amide peak due to the chemical imidization.

For example in the case of fluoro-poly(ether imide), based on 6FDA and p-SED, (i.e.

[6FDA + p-SED]), the FT-IR spectra of poly(ether amic acid) and poly(ether imide)

177

showed distinct features. The characteristic absorption bands of amides and carboxyl

groups in the spectra at 3240 to 3320cm-1 and 1500 to 1730cm-1 region disappeared and

those of imide ring appeared near 1784cm-1 (asym. C=O stretching) and 1728cm-1 (sym.

C=O stretching), 1376cm-1 (C-N stretching) 1063cm-1 and 744cm-1 imide (ring

deformation). Also the aryl-ether absorption band around 1250cm-1 for both amic-acid

and imide was very strong, indicating stability of the structure and successful conversion

of poly(ether amic acid) to poly(ether imide). Similar observation was made for rest of

the polymers.

Figure-9: FT-IR spectra of [6FDA + p-SED] fluoro-poly(ether amic acid) and fluoro-poly(ether imide) The chemical structures of the repeat units of two series of fluoro-copoly(ether imide)s

prepared and ULTEM1000 and KaptonH are shown in Figure 10. Similarly, the chemical

structures of the repeat units of polyimides, fluoro-polyimides and fluoro-copolyimides

prepared for dielectric properties studies are shown in Figure 11.

4000 3500 3000 2500 2000 1500 1000 500

[6FDA + p-SED] (6F-PEI)

744.311061.07

1250.33

1376.08

1728.1

1784.4

725.29

1258.01

1545.721664.22

1724



C-N StretchingimideSym C=O

StretchingImide

Asym C=OStretchingImide

C-N Bending

Aryl-Ether Stretching PEA

Amide ll

Amide

C=O strechingAmide lN-H and O-H group

3240 - 3320

Polyetherimide

Polyether-amic Acid

[6FDA + p-SED] (6F-PEAA)

%T

Wavenumber (cm-1)

4000 3500 3000 2500 2000 1500 1000 500


744.311061.07

1250.33

1376.08

1728.1

1784.4

725.29

1258.01

1545.721664.22

1724




StretchingImide


C-N Bending


Amide ll

Amide


3240 - 3320

Polyetherimide

Polyether-amic Acid


4000 3500 3000 2500 2000 1500 1000 5004000 3500 3000 2500 2000 1500 1000 500


744.311061.07

1250.33

1376.08

1728.1

1784.4

725.29

1258.01

1545.721664.22

1724




StretchingImide


C-N Bending


Amide ll

Amide


3240 - 3320

Polyetherimide

Polyether-amic Acid


%T

Wavenumber (cm-1)

178

S

O

O

OC C

C

C

CF3

O O

O

N

C C

C

C

CF3

O O

O

NNC

O

CF3

CCH3

OOCH3

C C

C

C

CF3

O O

O

NNC

O

CF3

CCF3

OOCF3

C C

C

C

CF3

O O

O

NN

CF3

S

O

O

OCCC

CF3

O OCF3

C

CH3

OOCH3

C C

C

C

CF3

O O

O

NNCO

CF3

C

CF3

OOCF3

S

O

O

OC C

C

C

CF3

O O

O

CF3

n

O

n

n

Fluoro-poly(ether imide) : [6FDA + p-SED]

Fluoro-poly(ether imide) : [6FDA + BPADE]

Fluoro-poly(ether imide) : [6FDA + BDAF]

Fluoro-copoly(ether imide) : [6FDA + (n%) p-SED + (m%) BPADE]

n

n m

m

Fluoro-copoly(ether imide) : [6FDA + (n %) p-SED + (m%) BDAF]

CCH3

CN

C

O

O

C

C

O O

CH3

C

C

C

O O

O

NC

O

n

n

Kapton-H : [ PMDA + ODA]

ULtem-1000 poly(ether imide) : [ BPADA + m-PDA]

CF3

O

N

CO

N ONCO

CO

N N O

CO

N

CO

O

O

N

Figure-10 : Chemical structures of fluoro-poly(ether imide)s, fluoro-copoly(ether imide)s ULTEM1000 and KaptonH

179

C

C C

CO

O

O

N

O

O

N

CH3

H3C

[ODPA + m-Tolidine] Polyimide

[PMDA + 3,3'-ODA] polyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

[6FDA + m-PDA] Fluoro-polyimide

C

C C

CO

N

O

CCF3

CF3

O

N

O[6FDA + p-PDA] Fluoro-polyimide

C

C C

CO

N

O

CCF3

CF3

O

N

O CH3

CH3H3C

H3C

[6FDA + 1,4-Diamino Durene] Fluoro-polyimide

C

C C

CO

N

O

CCF3

CF3

O

N

O

O

[6FDA + 4,4'-ODA] Fluoro-polyimide

C

C C

CO

N

O

CCF3

CF3

O

N

O

CCF3

CF3

[6FDA + 4,4'-6F-Diamine] Fluor0-polyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

H3C CH3

H3C CH35050

[6FDA + 50% 1,4-Diamino durene + 50% p-PDA] Fluro-copolyimide

[6FDA+ 50 % 1,4 Diamino Dure + 50 % m-PDA] Fluoro-copolyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

5050

[6FDA + 50 % p-PDA + 50 % m-PDA] Fluor-copolyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

H3C CH3

H3C CH35050

n

n

POLYIMIDES (PI)

n

n

FLUORO POLYIMIDES (6F-PI)

n

n

FLUORO COPOLYIMIDES (6F-CoPI)

C

C C

CN N O

O

O

O

O

n

Figure-11 : Chemical structures of polyimides, fluoro-polyimides and fluoro-copolyimides.

180

3.5.3. Solubility

The solubility of all fluoro-poly(ether imide) and fluoro-copoly(ether imide) solid

polymers, ULTEM1000 pellets, KaptonH film were tested in acetone, NMP, THF,

DMAc, DMF, methylene chloride and conc. H2SO4. The observations are tabulated in

Table 7. It shows that all CoPEI and ULTEM1000 polymers were soluble at room

temperature in NMP, THF, DMAc, DMF and conc. H2SO4, and partially soluble on

heating in acetone. KaptonH was insoluble in all the solvents tested at room

temperature. However, all of these polymers were soluble in conc. H2SO4 except

KaptonH, which showed disintegration.

Table-7: Solubility of fluoro-copoly(ether imide)s, ULTEM1000 solids and KaptonH films

Polymer Composition Acetone THF DMF DMAc BLO NMP CH2Cl2 H2SO4 [6FDA + p-SED] ± + + + + + + +

[6FDA + (75%) p-SED + (25%) BPADE] ± + + + + + + + [6FDA + (50%) p-SED + (50%) BPADE] ± + + + + + + + [6FDA + (25%) p-SED + (75%) BPADE] ± + + + + + + +

[6FDA + BPADE] ± + + + + + + + [6FDA + (75%) p-SED + (25%) BDAF] ± + + + + + - + [6FDA + (50%) p-SED + (50%) BDAF] ± + + + + + - + [6FDA + (25%) p-SED + (75%) BDAF] ± + + + + + - +

[6FDA + BDAF] ± + + + + + - + ULTEM 1000 ± ± + ± + + - +

Kapton H * - - - - - - - ±**

+: Soluble at room temperature, ±: Partially soluble upon warming, -: Insoluble polymer; *: As received Kapton H film, **: Polymer disintegrate; 3.5.4. Viscosity and molecular weights

The inherent viscosities and molecular weight data for 6F-PEAA, 6F-CoPEAA, 6F-

PEI and 6F-CoPEI are reported in Table 8, and for PEAA, 6F-PAA, 6F-CoPAA, PI, 6F-

PI and 6F-CoPI are reported in Table 9 respectively. It is important to control molecular

weights and molecular weight distribution during polymerization to have desirable and

useful physical and thermo mechanical properties. The result suggests that polymers

have reasonably high viscosity supported by reasonably high molecular weights which is

indicative of a reasonably high degree of polymerization.

The illustrative chromatograms of selected few 6F-PEI and 6F-CoPEI are given in

181

Figure-12 : GPC of [6FDA + p-SED] fluoro-poly(ether imide) polymer

Figure-13 : GPC of [6FDA + (50%) p-SED + (50%) BPADE] fluoro-copoly(ether imide) polymer

Figure-14 : GPC of [6FDA + BPADE] fluoro-poly(ether imide) polymer

182

Figure-15 : GPC of [6FDA + (50%) p-SED + (50%) BDAF] fluoro-copoly(ether imide) polymer

Figure-16 : GPC of [6FDA + BDAF] Fluoro-poly(ether imide) polymer Figures 12 to 16. The raw data were processed automatically using polystyrene standard

calibration curve by the GPC system, and the molecular weights of polymer were

calculated. Tables 8 and 9 shows that polymers with reasonably high molecular weight

with narrow polydispersity between 1.5 and 1.8 were obtained. These polymers because

of their high molecular weights are expected to have desirable and useful physical and

thermo mechanical properties. The lower inherent viscosities for solid 6F-PEI and 6F-

CoPEI than the 6F-PEAA and 6F-CoPEAA were attributed to the reduction of the

hydrodynamic volume in polymer because of the imide ring formation due to amic acid

conversion in imidization reaction.

183

Table-8: Solution and film properties of fluoro-poly(ether imide) and fluoro-copoly(ether imide), ULTEM1000 and KaptonH

Inherent Viscosity ηinh[dL/g]

GPC Molecular Weights

Polymer Composition

PEAA PEI Mw Mn d

[6FDA + p-SED] 0.91 0.83 123300 75960 1.6

[6FDA + (75%) p-SED + (25%) BPADE] 0.87 0.83 119200 76.15 1.6

[6FDA + (50%) p-SED + (50%) BPADE] 0.79 0.71 117660 73150 1.6

[6FDA + (25%) p-SED + (75%) BPADE] 0.85 0.77 122300 74450 1.6

[6FDA + BPADE] 0.92 0.80 129700 72190 1.8

[6FDA + (75%) p-SED + (25%) BDAF] 0.77 0.70 115540 75420 1.5

[6FDA + (50%) p-SED + (50%) BDAF] 0.87 0.8 140100 90100 1.6

[6FDA + (25%) p-SED + (75%) BDAF] 0.75 0.72 124810 80600 1.5

[6FDA + BDAF] 0.80 0.72 132170 83100 1.6

ULTEM 1000 NA 0.78 56400 40400 1.4

Kapton H * NA INS NA NA NA

*: As received film, INS: Insoluble, NA: Not available

183

184

Table-9 : Solution, thermal and electrical properties of polyimides, fluoro-polyimides and fluoro-copolyimide solid and films

Inherent Viscosity

(dL/g)

Molecular weights by GPC

TGA 5%Wt loss

(°C)

Composition

PAA PI Mw Mn d

Density (g/cc)

DSC Tg

(°C) Air N2

DEA Dielectric Constant @ 1kHz

(ε′)

Film characteristics

Fluoro-polyimides [6FDA+ m-PDA]

0.39 0.30 54133 31944 1.7 1.334 296 629 561 3.05 Yellow color flexible film

[6FDA+ p-PDA]

0.44 0.37 43067 23973 1.8 1.396 353 545 558 3.042 Yellow color brittle film

[6FDA + Durene]

0.60 0.58 145384 90880 1.6 1.385 424 488 531 2.90 Amber color flexible film

[6FDA + 4,4-6F-Diamine]

0.8 0.78 95850 53250 1.8 1.470 320 520 555 2.80 Clear colorless flexible film

[6FDA + ODA]

1.15 1.0 134515 84599 1.6 1.654 300 465 450 3.01 Very light yellow flexible film

Fluoro-copolyimides [6FDA+ (50%) m-PDA + 50% Durene]


[6FDA + (50%) p-PDA + (50%) Durene]


[6FDA + (50%) p-PDA + (50%) m-PDA]


Polyimide from poly(amic acid)s [ODPA + m-Tolidine]

0.97 NA Na NA NA NA 335 520 545 3.48 Pale yellow color flexible film

[PMDA + 3,3 ODA]

0.54 NA NA NA NA NA 385 510 495 3.468 Dark Amber color flexible film

[BPDA + m-PDA]

0.66 NA NA NA NA NA 340 540 560 3.47 Dark Amber color flexible film

184

185

3.5.5. Color and transparency of polymer films

The fluoro-poly(ether imide) films were very lightly colored to almost colorless as

compared to light amber to amber colored ULTEM1000 and KaptonH films,

respectively, as reported in Table 10. The polymer film thickness ranged from 25.0 to

37.5µm and thicker sample of [PMDA + 3,3-ODA] had a thickness of 55µm. The films

of fluoro-poly(ether imide)s [6FDA + p-SED] and [6FDA + BDAF] had almost identical

thickness. Koton et al. [64] explained that the transparency of visible light by polyimide

films is closely associated with the electronic characteristic of the monomer used in the

synthesis. Many non-fluorinated polyimide films are known to have yellow to dark

amber colors, whereas, the fluorinated polyimide films are almost colorless. The

incorporation of bulky fluorine-containing groups in the polyimide structure would

reduce refractive index and optical loss. Controlling the degree of fluoridation in

polyimides allows one to obtain a desired refractive index and transparency. Optical

transparency to visible light is affected by intra- and inter-molecular interactions of π

electrons between the monomer moieties in the polymer chain inducing a charge transfer

complex (CTC). The π electron transfers from the electron-donating diamine to the

electron acceptor dianhydride moiety.

The polyimide chain is basically composed of alternating donor and acceptor moieties,

which can interact with each other, inducing inter-chain CTC. It is therefore, possible to

reduce CTC by incorporating electronegative fluorine groups on the polymer backbone

or incorporating bulky electron withdrawing substituent groups, as they restrict the inter-

chain conformational mobility and thus lower the CTC [64, 83-86].

186

Table-10 : Fluoro-poly(ether imide) and fluoro-copoly(ether imide) polymer films characteristics and moisture uptake

Film

Polymer Composition Characteristic

Thickness

[µm]

Moisture

Absorption [%]

[6FDA + p-SED] Very light. brown to almost colorless transparent and flexible 27.5 0.5

[6FDA + (75%) p-SED+ (25%) BPADE] Pale yellowish transparent and flexible 32.5 0.8



[6FDA + BPADE] Light yellowish transparent and flexible 35.0 1.05

[6FDA + (75%) p-SED + (25%) BDAF] Very light. brown to colorless transparent and flexible 32.5 0.6

[6FDA + (50%) p-SED+ (50%) BDAF] Very light. brown to colorless transparent and flexible 30.0 0.6

[6FDA + (25%) p-SED+ (75%) BDAF] Very light. brown to colorless transparent and flexible 30.0 0.6

[6FDA + BDAF] Very light yellow to colorless transparent and flexible 27.5 0.55

ULTEM 1000 Light amber and flexible 25.0 1.52

Kapton H * Amber and flexible 25.0 3.0

* :As received film

186

187

3.5.6. Moisture uptake

The water absorption and diffusion properties of polymers are of great importance

with regards to their practical use in the microelectronics. The absorbed water in polymer

structures affects their performance and long term stability [87]. Very significant lower

moisture absorption values for hydrophobic hexafluoroisopropylidene (-C(CF3)2-) groups

containing 6F-PEI and 6F-CoPEI films at 100 RH at 50°C were noted. These values

were in the range of 0.3 to 1.05% for both series of fluoro-copoly(ether imide)s (Table

10). These values were lower than those of non-fluorinated poly(ether-imide)s, such as

ULTEM1000 (1.52%) and KaptonH (3.0%) films at 100 RH at 50°C, which were used

as 'controls' in this study. The % moisture absorption values measured in our study for

ULTEM1000 and KaptonH films were found to be similar to those reported in their

product brochures (1.25% at 23°C for 50% RH and 2.9% at 23°C for 100% RH)

respectively [21-23, 88-90]. The highly transparent polyimides with low moisture

absorption are suitable for wave-guide applications in opto-electronics [91].

3.5.7. Glass transition temperature (Tg)

The experimentally determined glass transition temperatures of fluoro-copoly(ether

imide) series [6FDA + (n mole%) p-SED + (m mole%) BPADE] and [6FDA + (n

mole%) p-SED + (m mole%) BDAF] by DSC and the calculated glass transition

temperatures by the Fox equation [47] are given in Table 11. The thermographs of both

series of 6F-CoPEI polymers [6FDA + (n mole%) p-SED + (m mole%) BPADE] and

[6FDA + (n mole%) p-SED + (m mole%) BDAF] are also shown in Figures 17 and 18.

A wide range in Tg values reflects the large variation in molecular structures. Glass

transition temperature decreased with decrease of p-SED content in [6FDA + (n mole%)

p-SED + (m mole%) BPADE] and [6FDA + (n mole%) p-SED + (m mole%) BDAF]

fluoro-copoly(ether imide) series. Among the fluoro-poly(ether imide) (homopolymers),

188

[6FDA + p-SED] had the highest glass transition temperature followed by [6FDA +

BDAF] and [6FDA + BPADE]. This was also consistent with the reduction in bulkiness

of the substituent group in the diamine structures of the polyimide chain [24, 80, 85-86,

92-93].

Figure-17: Glass transition (Tg °C) of fluoro-copoly(ether imide) series [6FDA + (n mole%) p-SED + (m mole%) BPADE] Figure-18: Glass transition (Tg °C) of fluoro-copoly(ether imide) series [6FDA + (n mole%) p-SED + (m mole%) BDAF]

-2.1

-1.9

-1.7

-1.5

-1.3220 230 240 250 260 270 280 290 300 310 320

Temperature (deg C)

Hea

t Flo

w (

W/g

)

6FDA + p SED

6FDA + 0.75 p SED + 0.25 BPADE



6FDA + BPADE

-2.2

-2

-1.8

-1.6

-1.4

-1.2

-1200 220 240 260 280 300 320 340 360 380 400

Temperature ( degC)

Hea

t Flo

w (W

/g)

6FDA + pSED

6FDA + 0.75 pSED + 0.25 BDAF

6FDA + 0.50 pSED + 0.50 BDAF

6FDA + 0.25 pSED + 0.75 BDAF

6FDA + BDAF

189

The glass transition temperature of copolyimides was calculated using Fox equation

[49] given below:

2

2

1

11

ggg TW

TW

T+= (1)

where W1 = Weight fraction of homopolymer 1;

W2 = Weight fraction of homopolymer 2;

Tg1 = Glass transition temperature of homopolymer 1

Tg2 = Glass transition temperature of homopolymer 2

The weight fractions of homopolymer 1 (W1) is calculated using the following equation

)()( 2211

111 MmMm

MmW+

= (2)

where m1 and m2 are molar fractions of homopolymer 1 and 2, and M1 and M2 are the

molecular weights of homo-poly(ether-imide) polymer 1 and 2 respectively.

Table-11: Experimental and calculated glass transition temperature of fluoro-copoly (ether imide)s

Diamine Composition

PSED (mole)

Tg (Exptl.) °C

Tg (Calc.) °C

∆Tg °C

BPADE (mole)

1.0 0.0 293 ---- ---- 0.75 0.25 278 284 + 6 0.50 0.50 268 276 + 8 0.25 0.75 260 267 + 7

0 1.0 259 ---- ----

BDAF (mole)

1.0 0.0 293 ---- ---- 0.75 0.25 278 286 +8 0.50 0.50 273 279 +6 0.25 0.75 270 273 +3

0 1.0 267 ---- ---- The experimentally found glass transition temperatures of fluoro-copoly(ether imide)s

[6FDA + (n mole%) p-SED + (m mole%) BPADE] and [6FDA + (n mole%) p-SED + (m

190

mole%) BDAF] by DSC were slightly lower than the theoretical value calculated using

Fox equation as shown in Figures 19 and 20.

Figure-19 : Glass transition (Tg°C) as a function of BPADE content in [6FDA + (n mole%) p-SED + (m mole%) BPADE] polymer

Figure-20 : Glass transition (Tg°C) as a function of BDAF content in [6FDA + (n mole%) p-SED + (m mole%) BDAF] polymer 3.5.8. Thermal decomposition temperature and stability

The study of the thermal stability of a given polymer is very important for determining

its thermal performance at a given upper temperature use limits. For such studies,

isothermal thermogravimetric (I-TGA) analysis, dynamic thermogravimetric (D-TGA)

255

260

265

270

275

280

285

290

295

0 0.2 0.4 0.6 0.8 1 1.2

Mole percent of BPADE

Gla

ss tr

ansi

stio

n te

mpe

ratu

re

Tg (Exptl)

Tg (Calc)

265

270

275

280

285

290

295

0 0.2 0.4 0.6 0.8 1 1.2

Mole percent of BDAF

Gla

ss tr

ansi

stio

n te

mpe

ratu

re

Tg (Exptl)

Tg (Calc)

191

analysis, and long-term isothermal-aging weight-loss measurement techniques are used.

Of these three techniques, dynamic D-TGA is widely used because it requires only a

small quantity of sample, and the entire study is over in few hours. The 5% wt loss

results in air as well as in nitrogen by TGA for 6F-PEI and 6F-CoPEI series are given in

Table 12. However, we have also determined the polymer’s thermal stability by the long-

term isothermal-aging technique, and also confirmed its results with those obtained by

the thermal degradation kinetic study of polymeric materials through use of D-TGA data.

The thermo-oxidative stability (TOS) and thermo-mechanical properties of the fluoro-

poly(ether imide)s and fluoro-copoly(ether imide)s film samples are also reported in

Table 12. For all the polymers, the 5% weight loss in nitrogen environment was observed

at about 10-20°C temperature higher than in the air environment , with the % char yield

(residue) in nitrogen was found to be in the range of 53 to 57% at 800°C. For all the

samples, the 100% decomposition, i.e., 0% residue was obtained in the air at the

temperature in the range of 650 to 700°C.

3.5.9. Thermal stability and degradation kinetic study

There are many kinetic methods available in the literature to study the thermal

degradation of polymeric materials [94]. Of these, the Coats and Redfern method [95] is

used here to evaluate the thermal stability of copolyimides. This method assumes a) that

only one reaction mechanism operates at a time; b) that the calculated activation energy

for degradation (Ea) value is for this mechanism and c) that product disappearance can be

expressed by the following basic rate equation

nkdtd )1( αα

−= (3)

For the thermogravimetric analysis, the fraction decomposed α is defined as the ratio of

actual weight loss to the totals weight loss corresponding to the degradation process, and

192

( )( )fMM

MM−−

=0

0α (4)

where

M is the actual weight of the sample

M0 is the initial weight of the sample

Mf is the final weight of the sample

"k" can be equated to "T” by the Arrhenius type equation:

RTEa

eAk−

= (5) where

A is frequency factor,

Ea is activation energy for the reaction,

T is temperature and

R is Universal gas constant.

For linear heating rate "φ " (deg / min)

dtdT=φ (6)

If reaction order (n) can be assumed to be one, then by utilising the above equations,

Coats and Redfern developed the following equation relating α with T.

−

−

=

−−

RTE

ERTAR

Ta

a

21ln)1(lnln 2 φα (7)

Where α is fraction decomposed at temperature T

φ is heating rate

Ea is activation energy

R is Universal gas constant

A is Arrhenius frequency factor

When the order of reaction is one, then the plot of ln [-ln (1-α) / T2] vs 1 / T gives a

straight line with slop equivalent to −Ea / R

193

Table-12 : Thermal and thermo-oxidative stability properties of fluoro-poly(ether imide) and fluoro-copoly(ether imide) films

Diamine Composition

TGA 5% Wt Loss

(°C)

p-SED (mole)

2nd Diamine (mole)

DSC Tg

(°C)

Air

N2

Char Yield in Nitrogen

(%)

TOS Weight retained @ 315°C for 300 hr

(%)

BPADE

1.0 0.0

293 544 561 52 97.7

0.75 0.25

278 537 625 57 97.5

0.50 0.50

268 583 613 55 94.3

0.25 0.75

260 535 619 57 86.1

0 1.0

259 527 559 56 84.0

BDAF

1.0 0.0

293 544 561 52 97.7

0.75 0.25

278 551 569 55 95.9

0.50 0.50

273 541 571 55 94.6

0.25 0.75

270 541 559 53 93.3

0 1.0

267 525 552 53 93.0

ULTEM1000

218 522 526 48 97.0

KaptonH

407# 601 603 53 95.6

193

194

Rao et al. [96] used the above equation to determine the activation energy for the

thermal degradation of polyimides based on diamine having ether ketone moiety. The

plots of ln [-ln (1-α) / T2] vs 1 / T for [ 6FDA + (n mole%) p-SED + (m mole%)

BPADE] and [6FDA + (n mole%) p-SED + (m mole%) BDAF] fluoro-copoly(ether

imide)s are given in Figures 21 and 23 respectively. The activation energy of thermal

degradation was calculated by multiplying universal gas constant value with the slope of

plot of ln [ -ln (1-α) / T2 ] vs 1 / T. Plots of activation energy vs mole percent of BPADE

and BDAF are given in Figures 22 and 24 respectively. Activation energy was found to

be decreasing with an increase in mole percent of BPADE and BDAF in [6FDA + p-SED

(n mole%) + BPADE (m mole%)] and [6FDA + (n mole%) p-SED + (m mole%) BDAF]

fluoro-copoly(ether imide)s series, respectively. In both the cases, the activation energy

decreased with decreasing p-SED content. However, he decrease was smaller for the

Figure-21 : Plot of ln [-ln (1-α) / T2 vs 1 / T of [6FDA + (n mole%) p-SED + (m mole%) BPADE] fluoro-copoly(ether imide) series

latter polymer series, indicating that [6FDA + (n mole%) p-SED + (m mole%) BDAF]

fluoro-copoly(ether imide)s were thermally better stable than [6FDA + (n mole%) p-SED

+ (m mole%) BPADE] fluoro-copoly(ether imide)s.

-17

-16

-15

-14

-13

-120.001 0.0011 0.0012 0.0013

6FDA - p SED6FDA - BPADE6FDA - 0.25 BPADE - 0.75 p SED6FDA - 0.50 BPADE - 0.50 p SED6FDA - 0.75 BPADE - 0.25 pSED

ln [

- ln

(1 -

α) /

T 2

1/T ( °K)

-17

-16

-15

-14

-13

-120.001 0.0011 0.0012 0.0013


-17

-16

-15

-14

-13

-120.001 0.0011 0.0012 0.0013


ln [

- ln

(1 -

α) /

T 2

1/T ( °K)

ln [

- ln

(1 -

α) /

T 2

1/T ( °K)

195

Figure-22 : Plot of activation energy vs mole % of BPADE in [6FDA + (n mole%) p-SED + (m mole%) BPADE] fluoro-copoly(ether imide) series polymers

Figure-23 : Plot of ln [-ln (1-α) / T2 vs 1 / T of [6FDA + (n mole%) p-SED + (m mole%) BDAF] fluoro-copoly(ether imide) series,

y = -8.002x + 34.723

0

5

10

15

20

25

30

35

40

0 0.2 0.4 0.6 0.8 1 1.2Mole percent of BPADE

Act

ivat

ion

ener

gy (K

cal /

mol

e)

-16.5

-15.5

-14.5

-13.5

-12.50.001 0.00105 0.0011 0.00115 0.0012 0.00125

6FDA - p SED

6FDA - BDAF

6FDA - 0.25 BDAF - 0.75 p SED

6FDA - 0.50 BDAF - 0.50 p SED

6FDA - 0.75 BDAF - 0.25 pSED

1/T ( °K)

ln [

-ln

(1 -

α) /

T 2

-16.5

-15.5

-14.5

-13.5

-12.50.001 0.00105 0.0011 0.00115 0.0012 0.00125

6FDA - p SED

6FDA - BDAF

6FDA - 0.25 BDAF - 0.75 p SED

6FDA - 0.50 BDAF - 0.50 p SED

6FDA - 0.75 BDAF - 0.25 pSED

1/T ( °K)

-16.5

-15.5

-14.5

-13.5

-12.50.001 0.00105 0.0011 0.00115 0.0012 0.00125

6FDA - p SED

6FDA - BDAF

6FDA - 0.25 BDAF - 0.75 p SED

6FDA - 0.50 BDAF - 0.50 p SED

6FDA - 0.75 BDAF - 0.25 pSED

1/T ( °K)

ln [

-ln

(1 -

α) /

T 2

196

Figure-24 : Plot of activation energy vs mole % of BPADE in [6FDA + (n mole%) p-SED + (m mole%) BDAF] fluoro-copoly(ether imide) series polymers 3.5.10. Thermo-oxidative stability (TOS) study

It is known that the 5% weight (loss) decomposition temperature by dynamic TGA

does not fully indicate the thermal performance of polymer at a given upper temperature

limits. Similarly, % char yield value obtained from TGA measurement under nitrogen

environment does not provide clear and direct information on actual ‘long term’ thermo-

oxidative stability of polymers. Therefore, isothermal thermo-oxidative stability (TOS)

measurements of fluoro-poly(ether imide)s: [6FDA + p-SED], [6FDA + BPADE] and

[6FDA + BDAF], and both series of fluoro-copoly(ether imide)s: [6FDA + (n mole%) p-

SED + (m mole%) BPADE] and [6FDA + (n mole%) p-SED + (m mole%) BDAF], and

ULTEM1000 and KaptonH films were carried out in a programmable oven at 315oC

for 300 hours in air environment. All these film samples were preheated at 150oC for one

hour and their weights at this point were taken as the reference or 100% weight value.

During the test, the crucibles with the samples were removed from the oven

simultaneously at appropriate times, and immediately sealed for cooling. They were

weighed and then returned to the oven immediately for further aging. Neglecting the

y = -4.4103x + 35.991

0

5

10

15

20

25

30

35

40

0 0.2 0.4 0.6 0.8 1 1.2Mole percent of BDAF

Activ

atio

n en

ergy

(Kca

l / m

ole)

197

initial weight loss of all the samples tested, which is thought to be associated with

solvent and absorbed moisture removal, an approximate weight loss between 2 to 16%

were obtain for the polymers studied. The plots of % weight retained against isothermal

heating time were plotted and given in Figures 25 and 26.

Figure-25 : Thermo-oxidative stability (TOS) of [6FDA + (n mole%) p-SED + (m mole%) BPADE] fluoro-copoly(ether imide) series polymers

Figure-26 : Thermo-oxidative stability (TOS) of [6FDA + (n mole%) p-SED + (m mole% ) BDAF] fluoro-copoly(ether imide) series polymers

80

85

90

95

100

0 25 50 100 150 200 250 300

TIME (HOUR)

% W

t. R

etai

ned

6 F D A - p S ED6 F + [7 5 p S ED + 2 5 B P A D E]6 F + [5 0 p S ED + 5 0 B P A D E]6 F + [2 5 p S ED / 7 5 B P A D E]6 F D A - B P A D EK A P T O N - HU L T EM 1 0 0 0

80

85

90

95

100

0 25 50 100 150 200 250 300Time ( Hours)

% W

eigh

t Ret

aine

d

6 FDA- pS ED6 FDA+[7 5 %pS ED+2 5 %BDAF]

6 FDA+[5 0 %pS ED+5 0 %BDAF]6 F+[2 5 pS ED+7 5 BDAF]6 FDA- BDAFKAP TO N- H

ULTEM 1 0 0 0

198

Table 12 also shows that only 2 to 3% weight loss occurred for [6FDA + p-SED] and

ULTEM100. Whereas, 4.4% weight loss for KaptonH, 5.57% weight loss for [6FDA

+ (50%) p-SED + (50%) BPADE], 5.4% weight loss for [6FDA + (50%) p-SED + (50%)

BDAF] and 7% weight loss for [6FDA + BDAF] and 16% weight loss for [6FDA +

BPADE] polymer occurred over 300 hours. The weight retention was lower for [6FDA +

(n mole%) p-SED + (m mole%) BPADE] copoly(ether imide)s series than for [6FDA +

(n mole%) p-SED + (m mole%) BDAF] copoly(ether imide)s series, especially when the

mole % value of n ≤ 75. This was attributed to faster air oxidation of isopropyl group

present in this series of polymers as compared to hexafluoroisopropylidene group present

in the latter series, indicating better thermo-stability of latter. The 97.7% weight retention

of [6FDA + p-SED] over 300 hours was the best observed among the materials tested.

The isothermal weight loss study also confirmed the thermo-stability explained by the

results obtained in the kinetic study using the Coats and Redfern method.

3.5.11. Thermomechanical properties

The thermo-mechanical properties of fluoro-polyetherimide film samples such as

storage modulus G' and loss modulus E" values are tabulated in Table 13. These

properties of polyimides are directly related to the inter- and intra-molecular chain

conformation rotation flexibility beside the chemical structure [97-98]. They also depend

on the previous heat history of the polymer samples. The results could be compared with

decreasing order of rigidity and/or stiffness and polarity of polymer backbone as

indicated by the varying value of glass transition temperature. The loss modulus E"

(Max) values were similar to Tg values. For all the samples tested, a dynamic loss peak

corresponding to β relaxation always observed near 100°C. This β relaxation is

considered to be due to inter-plane slippage of aromatic and imide rings [99].

199

Table-13: Thermo-mechanical properties of fluoro-copoly(ether imide) and fluoro-copoly(ether imide) films

Diamine Composition Storage Modulus* Loss Modulus*

E” ( Max) (°C)

P-SED (mole)

2ndDiamine (mole)

DSC Tg

(°C) 100°C 200°C

BPADE

1.0 0.0

293 187.4 139.1 293.3

0.75 0.25

278 143.2. 116.8 280.0

0.50 0.50

268 NA NA 269.0

0.25 0.75

260 176.5 139.0 263.0

0 1.0

259 199.4 158.1 256.3

BDAF

1.0 0.0

293 187.4 139.1 293.3

0.75 0.25

278 237.5 184.8 278.0

0.50 0.50

273 211.9 161.7 273.0

0.25 0.75

270 230.3 181.2 267.0

0 1.0

267 147.6 123.1 265.2

ULTEM 1000

218 179.3 116.5 223.3

Kapton H

407# 269.7 214.8 419.0

*: Measured by DMA, #: Measured by TMA of as received film, NA: Not Available.

199

200

3.5.12. Electrical properties

3.5.12.1. Dielectric properties of polyimides (PI) and copolyimides (Co-PI)

When a polymer film is placed between the parallel plates of dielectric analysis (DEA)

instrument and the electric filed is applied as shown in Figure 27, the net result of which

causes the polarization of polymeric materials through displacement of the positive and

negative charges within the atoms in the molecules of the polymer in opposite direction

and thus whole materials consequently become electrically polarized [100]. The electric

polarization of polymeric materials is in fact an electric dipole moment per unit volume.

Figure-27 : Molar polarization in polymer molecules

The dipole is defined as a chemical bond that has an unbalanced distribution of

charges in a molecule. The dipole can be induced by an applied electric filed or already

present in polar bonds, such as (C=O), within molecule. The permanent dipoles are those

due to the electro-negativity of bonded atoms in the absence of an applied electric filed.

Whereas an induced dipole is created by applied electric filed. The permittivity, i.e., the

dielectric constant (ε′) is due to an alignment of the dipoles when an electric field is

applied [100]. The permittivity of polymers are due to the combination of electronic

polarization and dipole orientation polarization of the polar groups, and the presence or

the absence of the polar groups in polymer’s molecular structure. In other words, the

polymers with polar groups have larger dipole moments and large dielectric constants,

Electron Accepting

Polyimide: UPILEX-R

C

C C

CO

O

O

N

O

N

O

n

δ− δ+

O2N N N NCH3

CH3

δ− δ+Dipole

Dipole Electron Donating

Electric Field

Electric Field

Electron Accepting

Polyimide: UPILEX-R

C

C C

CO

O

O

N

O

N

O

n

δ− δ+

O2N N N NCH3

CH3

δ− δ+Dipole


Electric Field

Electric Field

Electron Accepting

Polyimide: UPILEX-R

C

C C

CO

O

O

N

O

N

O

n

δ− δ+

O2N N N NCH3

CH3

δ− δ+Dipole


Electric Field

Electric Field

Electron Accepting

Polyimide: UPILEX-R

C

C C

CO

O

O

N

O

N

O

n

δ− δ+

O2N N N NCH3

CH3

δ− δ+Dipole


Electric Field

Electric Field

201

since their dipoles are able to orient in the applied electric field. The dielectric analysis of

polymer is therefore based on such interaction of polar groups in the polymer when

subjected to high and/or low electric filed. For electrical insulation applications in

microelectronics, the polymers typically without polar groups are preferred. The good

insulator exhibits very high resistivity, i.e., the current passing through them is extremely

low, and hence they can be used as interlayer dielectric [12, 15-20, 100].

Typically polymers are non conductors (i.e. good insulators). Their dielectric constants

may vary in the range of 1.0 to 10 (dimensionless) as compared to dielectric constant ε′=

1 for vacuum, ~1.0006 for air, and 81 for water at room temperature [101]. Most

polyimides inherently have low dielectric constant (ε′< 4.5).

3.5.12.1.1. Dielectric behaviour of the non-fluorinated polyimide (PI)

The chemical structure of the non-fluorinated polyimide [ODPA + m-Tolidine ] made

from oxydiphthalic dianhydride (ODPA) and 2,2-dimethyl- 4, 4-diaminobiphenyl (m-

Figure-28 : Dielectric properties of polyimide: [ODPA + m-Tolidine] at 1000Hz

Tolidine) is shown in Figure 11, and its dielectric properties were measured at 1000Hz.

and shown in Figure 28. It can be noted that starting from room temperature the

202

permittivity decreases with increasing in temperature. This is because polymer softens as

the temperature increases further, and hence its free volume increases. The peak is

observed above 100°C, which represents the β transition within the polymer chain due to

the conformational flip/mobility of aromatic cycles, which induces the ‘orientation

polarization’. At 1000Hz, the dielectric constants of [ODPA + m-Tolidine] polymer at

room temperature and 200°C were 3.48 and 3.342, respectively.

Figure-29 : Dielectric property of Upilex S [BPDA + p-PDA] polyimide Ube Industries, Ltd. Japan [22] reported that at 1kHz, the dielectric constant of

UPILEX-S at room temperature was 3.5. The dielectric measurement results obtained

in our laboratory on UPILEX-S film is shown in Figure 29. It shows a dielectric

constant of 3.47 at 1kHz at room temperature, which is close to Ube’s reported value.

3.5.12.1.2. Dielectric behaviour of the fluorine-containing polyimide (6F-PI)

Fluorination has been found to be the most effective means to influence this material

parameter [24-31]. The dielectric behavior of fluorine-containing polyimide: [6FDA + p-

3.5091Hz

3.4701000Hz

3.1

3.2

3.3

3.4

3.5

3.6

Per

mitt

ivity

20 40 60 80 100 120 140 160 180 200

Temperature (°C)

Sample: Upilex-S FilmSize: 0.0493 mmMethod: PI-filmComment: 3°/min, N2 500 cc/min, sputter coated

DEAFile: D:\RHV\PI-Upilex.008Operator: RHVRun Date: 13-Oct-98 19:14

Universal V2.5H TA Instruments

UPILEX-S [BPDA + p-PDA] Film3.5091Hz

3.4701000Hz

3.1

3.2

3.3

3.4

3.5

3.6

Per

mitt

ivity

20 40 60 80 100 120 140 160 180 200

Temperature (°C)




3.5091Hz3.5091Hz

3.4701000Hz

3.1

3.2

3.3

3.4

3.5

3.6

Per

mitt

ivity

20 40 60

3.4701000Hz

3.1

3.2

3.3

3.4

3.5

3.6

Per

mitt

ivity

20 40 60 80 100 120 140 160 180 200

Temperature (°C)




UPILEX-S [BPDA + p-PDA] Film

203

PDA] at 1000 and 10000Hz is shown in Figures 30 and 31, respectively. The β transition

peak moves toward a higher temperature with increasing frequency. The transition peak

points at 1000 and 10000 Hz are 200 and 240°C. The dependence of dielectric properties

of fluoro-polyimide [6FDA + p-PDA] on temperature is similar to that of non-fluorinated

polyimide: [ODPA + m-Tolidine], but the peak values of the fluoro-polyimide are lower

than those of the non-fluorinated polyimide.

Figure-30 : Dielectric properties of fluoro-polyimide [6FDA + p-PDA] at 1000Hz

Figure-31 : Dielectric properties of fluoro-polyimide [6FDA + p-PDA] at10000Hz

0.0032801000Hz

0.0099791000Hz

3.0421000Hz

0.01

0.02

[ ]

Tan

Del

ta

0 .00

0.02

0.04

0.06

0.08

0.10

[ ]

Los

s Fa

ctor

2 .2

2 .4

2.6

2.8

3.0

3.2

3.4

3.6

[ ]

Per

mitt

ivity

0 50 100 150 200 250 300

Temperature (°C)

Sam ple : 14213S ize: 0 .0496 m mMethod: P I-f ilmCom m ent: Multi Frequency S weep, N2 500 cc/m in , Sputter Coated for 45s

DEAFile : D :\W hm \14213O perator: whmRun Date : 5-Apr-99 10:55

Universal V2.3C TA Instrum ents

0.00518410000Hz

0.00170810000Hz

3.03510000Hz

0.01

0.02

[ ]

Tan

Del

ta

0.00

0.02

0.04

0.06

0.08

0.10

[ ]

Los

s Fa

ctor

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

[ ]

Per

mitt

ivity

0 50 100 150 200 250 300

Temperature (°C)

Sample: 14213Size: 0.0496 mmMethod: PI-filmComment: Multi Frequency Sweep, N2 500 cc/min, Sputter Coated for 45s

DEAFile: D:\Whm\14213Operator: whmRun Date: 5-Apr-99 10:55

Universal V2.3C TA Instruments

204

The dielectric constants of non-fluorinated [ODPA + m-Tolidine] and fluoro-

polyimide [6FDA + p-PDA] at room temperature are shown in Figure 32. The dielectric

constants of both non-fluorinated and fluoro-polyimides decreased with increasing

frequency. However, the fluorine-containing polyimide shows a much lower dielectric

constant.

Figure-32 : Dielectric constant (ε′), i.e., permittivity of non-fluorinated and fluoro-polyimides as a function of frequency 3.5.12.1.3. Dielectric behaviour of fluoro-copolyimides (6F-CoPI)

The chemical chain structural units of copolyimides consist of more than two

different monomer units. They may possess all the structural elements of a

homopolymer, but in reality, its structure varies by the change in molar% (amount) of

co-monomer in the polymer composition, and its sequence distribution (order) in the

polymer chain. The properties of copolymers mainly depend on the choice of co-

monomers and it molar% in the composition, its sequence distribution in the polymer

chain and polymer molecular weight distribution. In the case of homopolymers the

molecular weight distribution determines many important properties. However, in the

case of copolyimide, the additional knowledge of the co-monomer composition

distribution for copolymers is also very important, since it influences physical properties.

0.1 1 10 100 1000 10000 100000 10000002.8

3.0

3.2

3.4

3.6

3.8

ODPA-Bi-Tolu idine

6F+p-PDA

at room temperature

Per

mitt

ivity

Frequency, Hz

205

The co-monomer units may be incorporated at random, in regular alternation, or in block

or graft structures. Two copolyimides used in this study were random copolymers which

consist of [6FDA + (50%) Durene diamine + (50%) p-PDA] and [6FDA + (50%) p-PDA

+ (50%) m-PDA], respectively. Their chemical structures are shown in Figure 11.

The relationship between the dielectric constants of the two copolyimides as the

function of frequency at room temperature is shown in Figure 33. The dielectric

constants of both copolyimides also decreased with the increasing frequency, and are

similar to polyimides. However, the copolyimide: [6FDA + (50%) Durene diamine +

(50%) p-PDA] has a much lower dielectric constant than later.

Figure-33 : Dielectric constant (ε′), i.e., permittivity of fluoro-copolyimides : [6FDA + (50%) p-PDA + (50%) m-PDA] and [6FDA + (50%) Durene Diamine + (50%) p-PDA] The difference can be explained in term of their fractional free volume [FFV]. Chung

et al. [102] derived the FFV values for these polymers. It is known that the FFV is

indicative of relative chain packing, which also affects the glass transition temperature

(Tg) as well as the dielectric constant of the polymers [15, 38]. The higher the free

volume, the lower the dielectric constant. [38]. Table 14 shows Tg, FFV [100], and the

experimentally determined dielectric constant values.

0.1 1 10 100 1000 10000 100000 10000002.8

2.9

3.0

3.1

3.2

6F+p-PDA+m-PDA 6F+Durene+p-PDA

at room temperature

Frequency, Hz

Per

mitt

ivity

206

Table-14: Glass transition temperature (Tg), calculated fractional free volume (FFV) and dielectric constant (ε′) of fluoro-polyimide and fluoro-copolyimides

Polymer composition Tg (°C)

Calculated Fractional Free Volume [FFV]*

Dielectric Constant (ε′)

[6FDA + Durene] 424 0.183 2.90 [6FDA + (50%) Durene Diamine + (50%) p-PDA] 378 0.176 2.98 [6FDA + p-PDA] 353 0.167 3.04 [6FDA + (50%) Durene Diamine + (50%) m-PDA] 357 0.178 3.0 [6FDA + m-PDA] 296 0.164 3.05 [6FDA + (50%) m-PDA + (50%) p-PDA] 326 0.166 3.05

* : Ref.[102] It can be seen that at the Tg and FFV increased from low for [6FDA + m-PDA] to the

highest for [6FDA + Durene], and it was intermediate for the copolymer [6FDA + 50%

Durene Diamine + (50%) m-PDA] and [6FDA + 50% Durene Diamine + 50% p-PDA] at

the same time its measured dielectric constant decreased as well. However, it was

observed for the 2nd set of fluoro-copolyimide [6FDA + 50% m-PDA+ 50 % p-PDA]

which does not have durene diamine, and therefore its chain packing was not altered

significantly to effect any noticeable increase in its FFV, and hence, there was no

decrease in its measured dielectric constant.

3.5.12.2. Estimation of dielectric constant (ε′) of polyimides and copolyimides

The development of polyimides with a low dielectric constant is one of the important

research directions. It was noted that except one [38] all the references reviewed [38-45,

103-107] have used either Maxwell’s relationship (ε′= n2) [108] or Maxwell-Garnett

theory [38, 109]. However, a limitation arises for these methods, in that one must have

on hand several polymers synthesized beforehand and characterized for their refractive

indices (n). Only then, one can calculate the dielectric constant (ε′) using the above

equations. Hence, before synthesis and characterization, there is no guarantee that these

polymers will have the desired dielectric constants. Therefore, an emphasis has been

placed on the use of the ‘estimation’ method by “additive group contribution” as defined

by Lorentz and Lorenz theory and Vogel theory [38, 46-47] for calculating

207

(predetermining) dielectric constant value of polyimides before the actual synthesis. In

addition, two empirical mathematical equations based on these theories were further

derived, expanded and simplified for calculating estimated dielectric constant value for

copolyimides. These new equations are called the Vora-Wang equations [48]. Using

these equations, the estimated values were calculated, which were found to be in good

agreement with both the experimental and literature values within the ± 0.1-10%

standard deviations.

3.5.12.2.1. Estimation of dielectric constant (ε′) of polyimides (PI)

Polyimides are different from other polymers since their chemical structures contain

some special conjugated groups, such as the ‘Phthalimide’ group or the

‘pyromellitimide’ group. Almost all aromatic polyimides and copolyimides have either

of these groups.

3.5.12.2.1.1. Calculation of ‘Molar Polarization’ of ‘Phthalimide’ groups

According to the Lorentz and Lorenz theory and Vogel theory, the molar polarization

of organic group is not equal to the sum of its atomic polarization values. However, the

molar polarization can be obtained through actual measurements. The chemical structure

of ‘Phthalimide’ is shown below:

C

O

NCO

The molar polarization of a dielectric material by the Lorentz and Lorenz theory and

Vogel theory, respectively can be defined as follows:

VPLL 2'1'

+−

=εε

(8)

MPV 'ε= (9)

208

Upon rearranging Eq. (8) and (9), the dielectric constant, (ε′) are expressed as follows:

LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

where

PLL is Molar polarization (for Lorentz and Lorenz theory in Eqs. (8) and (10)

PV is Molar polarization (for Vogel theory in Eqs. (9) and (11)

M is Molar mass of contributing group/s

V is Molar volume (at 298 K).

To estimate the dielectric constant of any aromatic polyimide having Phthalimide

groups, it is very important that one must first calculate the “molar dielectric

polarization” value PLL and PV of the ‘Phthalimide’ groups. Literature review indicates

that no attempts were ever made before to determine these values using the chemical

structure of UPILEXS polyimide [22, 38,-47, 103-109]. Interestingly, the repeat unit of

this polyimide has two ‘Phthalimide’ groups and one ‘p-Phenylene’ group. The

chemical structure of the repeat unit of polyimide UpilexS, [BPDA + p-PDA] in given

below.

Ube Industries, Ltd. Japan [22] reported that for Upilex-S, the dielectric constant

(permittivity) ε′ was 3.5 at 1000Hz at room temperature (25°C). The experimental DEA

results on UpilexS film obtained in our laboratory, as shown in Figure 29 and reported

nC

O

NC

O

C

O

NCO

209

in Table 15, show a dielectric constant ε′ of 3.47 at room temperature at 1000Hz. This

value is very close to the reported value. Using the experimental value for the dielectric

constant ε′ of UPILEXS as 3.47 at 1kHz, and knowing the molar mass M = 366.3 and

the molar volume V = 282.5 at room temperature (298K) of the Phthalimide group and

other chemical groups [38] present in the repeat unit of UPILEXS, one can obtain, by

means of the additive group contributions method [38, 46-47], the molar dielectric

polarization value X by Eq. 8 for the Lorentz and Lorenz theory and the molar dielectric

polarization value Y by Eq. 9 for the Vogel theory for this special ‘Phthalimide’ group as

follows:

Group Contribution of Molar Polarization No. of

Groups GROUP PLL V PV M

2 C

O

NCO

2xX

2x108.50 2xY 2x145.10

1

1x25.00

1x 65.50 1x128.60 1x 76.10

∑ 2X+25 282.50 2Y+128.6 366.30

Using equation (8) and (9), one can calculate the molar polarization values X and Y of

this ‘Phthalimide’ group alone:

PLL = 2X + 25 = [(3.47 - 1)/(3.47 + 2)] x 282.5

∴X = 51.28 for the Lorentz and Lorenz theory, by Eq. (8) and

PV = 2Y + 128.6 = 3.47 ½ x 366.3

∴Y = 276.59 for the Vogel theory by Eq. (9)

3.5.12.2.1.1.A. Estimation of dielectric constant of poly(ether imide) ULTEM1000 [BPADA + m-PDA]

Now, using the above molar polarization values, X for PLL and Y for PV for special

‘Phthalimide’ group, and equations (10) and (11) given above, one can easily estimate

210

the dielectric constant of commercially available non-fluorinated poly(ether imide)

ULTEM1000 [BPADA + m-PDA], whose chemical structural repeat unit is given

below. Also by comparing the estimated value with the experimental and literature value,

the usefulness of the values X and Y for the special ‘Phthalimide’ group could be

verified and established.

O

n

CO

NCO

CO

NCO

CCH3

CH3

O

By means of the above calculated X and Y values, and other group contributions

values given in reference [38], one can calculate the dielectric constant of [BAPDA + m-

PDA] poly(ether imide) using equations (10) and (11), as follows:



2 C

O

NCO

2x 51.28

2x108.50 2x 276.59 2x145.10

2

2x25.00

2x 65.50 2x128.60 2x 76.10

1

25.00

69.00 128.60 76.10

2

– O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

1

CH3-C-CH3–

13.90

49.00 61.70 42.00

∑ 201.86 483.00 1060.68 592.50

Using equation (10) and (11), one can calculate the dielectric constant, ε′ as.

ε′ = (2x201.86 + 483.00) ÷ 483.00 - 201.86) = 3.154 by the Lorentz and Lorenz’s

theory, Eq. (10) and

ε′ = (1060.68 ÷ 592.50)2 = 3.205 by the Vogel’s theory, Eq. (11)

211

Literature reported the dielectric constant ε′ of 3.15 at 1 kHz and 25°C for

ULTEM1000 [23], which on comparison found to be 0.1% and 1.75% less than the

calculated (estimated) values by Eq. (10) and (11), respectively. At the same time, our

experimental value for dielectric constant was 3.178 at 1 kHz and 25°C as reported in

Table 15 which is about 1.03% more and 1.52% less than the values calculated by Eq.

(10) and Eq. (11) respectively. However, the literature values on final comparison

were found to be in excellent agreement with the experimental value as well as the

estimated values.

Similarly the estimated dielectric constant values of UPILEXR [BPADA + 4,4-

ODA] were 3.38 and 3.36 for the Lorentz and Lorenz theory, Eq. (10), and the Vogel

theory, Eq. (11) respectively. These values were in good agreement with the literature

value [22] of 3.5. The literature values were about 3.43% and 4.0% higher than estimated

value. However, both these calculations undoubtedly establishes the usefulness of values

of X and Y for the special ‘Phthalimide’ group. It was further confirmed by calculating

the dielectric constant (ε′) of several other non-fluorinated and fluoro-polyimides

synthesized in the lab (Table 9) as well as reported in the literature [33]. The calculated,

experimental and literature values of dielectric constant of these polymers are given in

Tables 16 and 17. The systematic calculations of estimated dielectric constants of these

polymers were given in Appendix-B at the end of thesis.

3.5.12.2.1.2 Calculation of ‘Molar Polarization’ of ‘Pyromellitimide’ group

In addition, it is similarly of interest to calculate the molar dielectric polarization

values of another important ‘Pyromellitimide’ group from the structural repeat unit of

commercial polyimide Kapton-H. This is another very important value for the

estimation of dielectric constant of polyimide having such a group.

212

C

O

N

C

O

C

C

O

O

N

The chemical structure of ‘Pyromellitimide’ group is given above, and the structural

repeat unit of KaptonH, [PMDA + 4,4-ODA] is given as follows:

The literature value for the dielectric constant ε′ of KaptonH is 3.5 at 1kHz at room

temperature (25°) [21], and also reported in Table 16. Knowing the molar mass M =

382.3 and the molar volume V= 290.5 at room temperature (298K) of the

Pyromellitimide group and other chemical groups [38] present in the repeat unit of

KaptonH, one can obtain by means of the group contributions method [38, 46-47], the

molar dielectric polarization values: X' by the Lorentz and Lorenz’s theory, equation (8),

and molar dielectric polarization value Y' by the Vogel’s theory, equation (9) for the

special Pyromellitimide’ group as follows:



1 C

C C

CN N

O

O

O

O

1xX′

2x151.00 1xY′ 1x214.10

2

2x25.00

2x65.50 2x128.60 2x 76.10

1 – O –

1x 5.20

1x 8.5 1x 30.00 1x 16.00

∑ X′+55.20 290.50 Y′+287.2 382.30

Using equation (8) and (9) one can calculate the molar dielectric polarization values

for this special ‘Pyromellitimide’ group as follows;

PLL = (X′ + 55.20) = [(3.50-1) ÷ (3.50+2) x 290.50] = 78.845 by equation. (8)

O

C

O

N

C

O

C

C

O

O

N

n

213

PV = (Y′ + 287.2) = [(3.50)1/2 x 382.3] = 428.02 by equation. (9)

Therefore,

∴X′ = 78.845 for the Lorentz and Lorenz’s theory, Eq. (8) and ∴Y′ = 428.02 for the Vogel’s theory, Eq. (9). 3.5.12.2.1.2.A Estimation of dielectric constant of [PMDA + 3,3-ODA] polyimide

Using the above molar polarization values, X′ for PLL and Y′ for PV of special

‘Pyromellitimide’ group, and equations (10) and (11) given above, one can easily

estimate the dielectric constant of polyimide [PMDA + 3,3-ODA], which is a meta-

analogue of [PMDA + 4,4-ODA] polymer. By comparing the calculated value with the

experimental as well as literature value, we have verified and established the usefulness

of the values X' and Y' for the special ‘Pyromellitimide’ group as follows:

The structural repeat unit of polyimide [PMDA + 3,3-ODA] is given below:

Group Contribution of Molar Polarization

No. of Groups

GROUP PLL V PV M

1 C

C C

CN N

O

O

O

O

1x76.845

2x151.00 1x428.02 1x214.10

2

2x25.00

2x 69.00 2x128.60 2x 76.10

1 – O –

1x 5.20

1x 8.5 1x 30.00 1x 16.00

∑ 132.045 297.50 715.22 382.30

Now using the Lorentz and Lorenz’s theory equation (10) and the Vogel’s Theory (11)

respectively, the estimated dilectrci constant values were calculatedas follows::

ε′ = (2x132.045 + 297.50) ÷ 297.50-132.045) = 3.39 by the Lorentz and Lorenz’s

O

CO

NCO

C

CO

O

Nn

214

theory, Eq. (10) and

ε′ = (715.22 ÷ 382.30)2 = 3.50 by the Vogel’s theory, Eq. (11)

The experimentally measured dielectric constant ε′ of [PMDA + 3,3-ODA] at 1kHz

and 25°C for 37.5µm thick film was 3.42 as shown in Figure 34. The experimental value

was 0.88% higher and 2.34% lower than the values calculated by Eq. (10) and Eq. (11),

respectively.

Figure-34 : Dielectric properties of [PMDA + 3,3-ODA] polyimide

The estimated dielectric constant values for [PMDA + 3,3-ODA] are also in good

agreement with the experimental as well as literature values. Thus, once again, it also

establishes the usefulness of the values X' and Y' for the special ‘Pyromellitimide’

group.

Also, Tables 15 and 16 show that the calculated values for non-fluorinated polyimides

synthesized in the lab and well as the commercially available polyimides: UPILEXS,

UPILEXR KaptonH and ULTEM1000, are in good agreement with the experimental

as well as literature values. The systematic calculations of dielectric constant values of

these polymers were been given in Appendix-B at the end of thesis.

3.4681Hz

3.4201000Hz

2.8

3.0

3.2

3.4

3.6

3.8

Per

mitt

ivity

20 40 60 80 100 120 140 160 180 200

Temperature (°C)

Sample: PI Film 20-01-99Size: 0.0304 mmMethod: PI-filmComment: 3°C/min, N2 500 cc/min, Sputter coated for 45s

DEAFile: D\RHV\PI Film 20-01-99Operator: WHMRun Date: 20-Jan-99 17:25


[PMDA + 3,3’ODA] Polyimide Film3.4681Hz

3.4201000Hz

2.8

3.0

3.2

3.4

3.6

3.8

Per

mitt

ivity

20 40 60 80 100 120 140 160

3.4681Hz

3.4201000Hz

2.8

3.0

3.2

3.4

3.6

3.8

Per

mitt

ivity

20 40 60 80 100 120 140 160 180 200

Temperature (°C)

Sample: PI Film 20-01-99Size: 0.0304 mmMethod: PI-filmComment: 3°C/min, N2 500 cc/min, Sputter coated for 45s

DEAFile: D\RHV\PI Film 20-01-99Operator: WHMRun Date: 20-Jan-99 17:25


[PMDA + 3,3’ODA] Polyimide Film

215

Table-15 : Comparisons of the estimated dielectric constant values with the experimental as well as literature values of commercially available non-fluorinated polyimides

Estimated Value (ε′)

Polyimides

Equation (10)

Equation (11)

Experimental Value

(ε′) at 1kHz

Literature Value

(ε′) at 1kHz

Kapton- H [PMDA + 4,4-ODA] -- -- 3.45 ** 3.50 1 UPILEX-S [BPDA + p-PDA] -- -- 3.47 3.50 2 UPILEX-R [BPDA + 4,4-ODA] 3.38 3.36 -- 3.502 ULTEM-1000 [BPADA + m-PDA] 3.15 3.21 3.18 3.15 3

1: Ref. [21]; 2: Ref. [22]; 3: Ref. [23] Table-16 : Comparisons of the estimated dielectric constant values with the experimental as well as literature values of non-fluorinated polyimides


Polyimides

Equation (10)

Equation (11)

Experimental Value

(ε′) at 1 kHz

Literature Value

(ε′) at 1kHz

[ODPA + m-Tolidine] 3.18 3.22 3.48 NA BPDA + m-PDA 3.415 3.46 3.47 3.5 1 [PMDA + 3,3-ODA] 3.39 3.50 3.42 3.50 2

1: Ref. [33]; 2: Ref. [64]; 3.5.12.2.1.3. Estimation of dielectric constant of lab synthesized fluoro-polyimides

(6F-PI) For further verification of the molar dielectric polarization values (X and Y) for these

special ‘Phthalimide’ and ‘Pyromellitimide’ groups, the dielectric constants ε′ of

various synthesized fluoro-polyimides, such as [6FDA + Durene], [6FDA + p-PDA],

[6FDA + m-PDA], [6FDA + 4,4’-6F-Diamine] and [6FDA + 4,4-ODA] were estimated

and compared with their experimental as well as literature values. Their chemical

structural units are shown in Figure 11, and the estimation results are listed in Table 17.

For fluoro-polyimides, it can be seen that the estimated values are in good agreement

with the experimental values at 1kHz, whereas the literature values are slightly lower

than the estimated valued, but well within the 0.1-10% deviation range. Also the

literature values are reported for the high frequency values. We have also seen earlier in

the sections 3.5.12.1.2. and 3.3.12.1.3 of this chapter that the dielectric constants

decrease with increasing frequency.

216

Table-17 : Comparisons of the estimated dielectric constant values with the experimental as well as literature values of fluoro-polyimides


Polyimides

Equation (10)

Equation (11)

Experimental Value

(ε′) at 1 kHz

Literature Value

(ε′) at 1kHz

SIXEF-44 [6FDA + 4,4-6FDiamine]

2.88 2.72 NA 2.78 1

[6FDA + 4,4-ODA] 3.09 2.96 NA 2.90 2 [6FDA + p-PDA] 3.09 2.96 3.036 2.9 2 [6FDA + m-PDA] 3.06 2.96 3.045 3.0 2 [6FDA + Durene] 3.18 3.22 3.48 NA

1: Ref. [32]; 2: Ref. [33];

Figure-35: Influence of frequency and temperature on dielectric constant of polyimide [PMDA + 3,3-ODA] film of thickness 55µm. Besides, in the actual experimental measurements, the dielectric constant can also be

affected by changes in film thickness, humidity, temperature and electrical current

frequency used. The polyimide dielectric constant increases linearly as the humidity

increases from 10 to 100% [15, 110].

Similarly, frequency also changes a dielectric polymeric material’s relative

permittivity, as we have seen in case of higher thickness (55µm) rigid, non-polar

polyimide, [PMDA + 3,3- ODA] polyimides film sample. The experimental results as

shown in Figure 35 indicate that higher thickness film at room temperature gave slightly

higher dielectric constant (ε′ = 3.52) as compared to 3.42 for 37.5µm thick film, and the

0.1 1 10 100 1000 10000 100000 10000003.2

3.3

3.4

3.5

3.6

RT

200 oC

Per

mitt

ivity

Frequency, Hz

217

dielectric constant decreases not only with increasing frequency but also with increasing

temperature. This could be explained in terms of restricted conformation of rigid

polymer at low temperature and hence frozen intramolecular segmental movement, and

because of that dipole orientation and displacement polarization cannot rapidly follow to

the change of alternating electric field at sufficiently high frequencies. Beside that, at low

temperature, the presence of moisture (ε′ = 81), typically adsorbed on the polymer film

surface, would dramatically contribute toward a higher dielectric constant [15, 110].

Therefore, due to these reasons, a significant lowering of dielectric constant at increasing

frequency at room temperature was not observed. However, at high temperature and

increasing frequency there is some segmental movement within the polymer structure as

well as the loss of moisture from the polymer film surface. Therefore, the dielectric

constant was found to be decreasing.

3.5.12.2.2. Estimation of dielectric constant of copolyimides (Co-PI)

In general, the chemical structure of a copolyimide consists of two or more structural

units. However, from our careful calculation and observation, it was determined that the

dielectric constant of a copolyimide does not follow the simple rule of group contribution

additivity of the dielectric constant values of its individual homopolymeric components.

Therefore, for estimation purpose, a copolyimide is assumed to be made up of two

structural units, 1 and 2. If the dielectric constants of individual units 1 and 2 are ε′1and

ε′2, respectively, then the dielectric constant of copolyimide, ε′CO, is not equal to the sum

of the dielectric constants of individual units 1 and 2, i.e.,

ε′CO ≠ nε′1 + mε′2 (12)

where, n and m are the molar fractions of units 1 and 2, respectively.

However, on further calculation exercise, it was established that the Polarization PLL

(Lorentz and Lorenz theory) and PV (Vogel theory) [38, 46-47], and Volume V and their

218

molecular weight (mass) M do follow the group contribution additivity, i.e.

21 LLLLLLCO mPnPP += (12a)

21 mVnVVCO += (12b)

21 VVVCO mPnPP += (12c)

21 mMnMM CO += (12d)

where PLL1, PLL2 and PLLCO are the molar dielectric polarization (Lorentz and Lorenz’s

theory) values for units 1, 2 and copolyimide structure, respectively

PV1, PV2, and PVCO, are the molar dielectric polarization (Vogel’s theory) values of

units 1, 2 and copolyimide structure, respectively

M1, M1 and MCO are the molar masses of units 1, 2 and copolyimide structure,

respectively

V1, V2 and VCO are the molar volumes of units 1, 2 and copolyimide structure,

respectively

By substituting these values from Eq. (12a), Eq. (12b), Eq. (12c), and Eq. (12d) into

equation (10) and (11), we have expanded and derived two new equations (13) and (14),

which are called the Vora-Wang Equations [48] for the calculation of estimated

dielectric constant for the copolyimide polymers:

)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)

By means of X and Y values derived earlier for the ‘Phthalimide’ and

‘Pyromellitimide’ groups, and the group contributions values provided for other

chemical groups in the literature [38], and substituting them in the Vora-Wang equations

219

(13) and (14), one can easily predetermine by estimation the dielectric constants of

different copolyimides structures. It is expected that the Vora-Wang equations can be

used for any organic copolyimides or copolymers with 2 or more co-monomer in its

structural repeat units.

3.5.12.2.2.1. Dielectric constant of the fluorine-containing copolyimide (6F-CoPI)

Using the Vora-Wang equations and the X and Y values derived earlier for the

‘Phthalimide’ and ‘Pyromellitimide’ groups, and the group contributions values

provided for other groups provided in literature [38, 48], we have estimated the dielectric

constants of three fluoro copolyimides (6F-CoPEI), such as: [6FDA + (50%) p-PDA +

(50%) m-PDA] and [6FDA + (50%) Durene + (50%) m-PDA] and [6FDA + (50%)

Durene + (50%) p-PDA], synthesized in our lab. Their chemical structural units are

shown in Figure 10, where n = m = 0.5. The estimated results are listed in Table 18. The

estimated values based on the Vora-Wang equations (13) and (14) were compared with

the experimental results. It can be seen that the estimated values are in good agreement

with the experimental values. This successful exercise un-equivocally establishes the

usefulness of the Vora-Wang equations and the molar polarization PLL (by Lorentz and

Lorenz theory) & PV (by Vogel theory) values derived for the ‘Phthalimide’ and

‘Pyromellitimide’ groups.

Table-18 : Comparisons of the estimation values and the experimental value of dielectric constant for fluoro-copolyimides


POLYIMIDES

Equation (13) Equation (14)

Experimental Value (ε′)

at 1 kHz [6FDA + (50%) p-PDA + (50%) m-PDA] 3.07 2.96 3.05 [6FDA + (50%) Durene + (50%) m-PDA] 2.94 2.88 3.00 [6FDA + (50%) Durene + (50%) p-PDA] 2.96 2.87 2.98

3.5.12.2.2.2. Dielectric constant of the fluoro-poly(ether imides) (6F-PEI) and

fluoro-copoly(ether imide)s (6F-CoPEI) The permittivity (ε′) of the dried film samples of fluoro-poly(ether imides) [6FDA +

220

p-SED], [6FDA + BPADE] and [6FDA+ BDAF], and both series of fluoro-copoly(ether

imide)s [6FDA + (n mole%) p-SED + (m mole%) BPADE] and [6FDA + (n mole%) p-

SED + (m mole%) BDAF], of thickness ranging from 25 to 35µm were measured at

room temperature and the values are reported in Table 19. The dielectric constants of

'control' samples of UPILEXS, KaptonH, and ULTEM1000 film sample measured in

lab are reported in Table 16 above. Their chemical structures are given in Figure 10.

It is very appropriate to once again point out here that the dielectric constants of these

series of designed fluoro-copoly(ether imide)s polymers discussed in this chapter were

predetermined by means of Vora-Wang equations, well before their actual synthesis in

our lab. The actual calculations of estimated dielectric constant values of all the above

polymers are given in Appendix-B at the end of the Thesis.

The estimated values by using Eq. 10 (Lorentz and Lorenz’s theory) [46] and Eq. 11

(Vogel’s theory) [47] for the three fluoro-poly(ether imide)s [6FDA + p-SED], [6FDA +

BPADE] and [6FDA + BDAF], were in good agreement with the experimental values at

1 kHz as well as with literature values. The estimated values by using Vora-Wang

equations (13) and (14) for both series of fluoro-copoly(ether imide), [6FDA + (n

mole%) p-SED + (m mole%) BPADE] and [6FDA + (n mole%) p-SED + (m mole%)

BDAF], were also in excellent agreement with the experimental values at 1 kHz at room

temperature. Table 19 also shows that the estimated values for these polymers were

slightly higher than some of the literature values, but well within ± 0.1-10% standard

deviation. This is because some of the literature values as reported were for high

frequency measurement. Also noted from Tables 15 and 19 that fluorine containing

poly(ether imide)s have lower dielectric constants as compared to the conventional

polyimide polymers, such as, ULTEM1000, UPILEXS, UPILEXR, and KaptonH,

which do not have trifluoromethyl groups in their structural backbone.

221

Table-19: Comparison of estimated, experimental and literature value of dielectric constant (ε’) fluoro-poly(ether imide) and fluoro-

copoly(ether imide) polymers

Estimated value (ε’)

Vora-Wang Equation Composition Lorentz & Lorenz’s Theory Eq. (10)

Vogel’s Theory Eq. (11) Eq. (13) Eq. (14)

Experimental Value ( ε’)

@ 1kHz

Literature Value (ε’)

[6FDA + p-SED

3.09 2.99 - - 3.10 2.74 a

[6FDA + (75%) p-SED + (25%) BPADE]

- - 3.09 2.94 3.09 NA

[6FDA + (50%) p-SED + (50%) BPADE]

- - 3.04 2.97 3.10 NA

[6FDA + (25%) p-SED + (75%) BPADE]

- - 3.01 2.90 3.05 NA

[6FDA + BPADE]

2.97 2.91 - - 3.04 2.65 b

[6FDA + (75%) p-SED + (25%) BDAF]

- - 3.08 2.34 3.10 NA

[6FDA + (50%) p-SED + (50%) BDAF]

- - 3.03 2.90 2.99 NA

[6FDA + (25%) p-SED + (75%) BDAF]

- - 2.98 2.83 2.98 NA

[6FDA + BDAF]

2.94 2.81 - - 3.0 2.99 c

a : Ref. [80-82, 111]; b : Ref. [33-36, 110]; NA : Not available

221

222

.5.12.2.2.2.A. Dielectric constant as a function of fluorine content in copoly(ether imide) polymers

A significant note was made from the data tabulated in Tables 17 and 19 that the overall

incorporation of fluorine atoms via trifluoromethyl groups’ attachment into polymer

backbone has produced low dielectric properties. Graphs of dielectric constant as a

function of the fluorine content for the both [6FDA + n mole% p-SED + m mole%

BPADE] and [6FDA + n mole% p-SED + m mole% BDAF] series of fluoro-

copoly(ether imide) polymers are given in Figures 36 and 37. It is evident from the

graphs that for both the series of fluorine-containing copoly(ether imide)s, the dielectric

constants decreased with the increase in fluorine-content in the copoly(ether-imide)

polymer’s repeat unit.

Figure-36 : Dielectric constant v/s Fluorine content in [6FDA + n Mole% p-SED + m Mole% BPADE] fluoro-copolyetherimide polymers A simple explanation could be provided that the polarization (electronic polarization and

dipole-oriented polarization) which contributes towards the total dielectric constant

values in polymer is decreased due to the incorporation of fluorine groups, thus causing

overall reduction in polar groups in fluoro-polyimides. Also small dipole and low

polarizability of (-C-F) bond as well as an increased free volume caused by the

replacement of isopropyl group by a bulky hexafluoroisopropyl group in their polymer

structure [15, 38] resulted in lower dielectric constant values. This observation is very

similar to those reported in the literature [4, 15, 29-34, 48, 51, 53, 61, 80-82, 89]

R2 = 0.9938

2.9

2.92

2.94

2.96

2.98

3

3.02

3.04

3.06

13.5 13.6 13.7 13.8 13.9 14

% Fluorine Content

Die

lect

ric

Con

stan

t

Series1

Poly. (Series1)

[6FDA + p-SED] [6FDA + 75 m% p-SED+25m% BPADE]

[6FDA + 50 m% p-SED+50 m% BPADE]


[6FDA + BPADE]

R2 = 0.9938

2.9

2.92

2.94

2.96

2.98

3

3.02

3.04

3.06

13.5 13.6 13.7 13.8 13.9 14

% Fluorine Content

Die

lect

ric

Con

stan

t

Series1

Poly. (Series1)

[6FDA + p-SED] [6FDA + 75 m% p-SED+25m% BPADE]



[6FDA + BPADE]

223

Figure-37 : Dielectric constant v/s Fluorine content in [6FDA + n Mole% p-SED + m Mole% BDAF] fluoro-copoly(ether-imide) polymers 3.5.12.2.2.3. Additional ‘Molar polarization values for calculation of dielectric

constant by additive group contribution Additional ‘molar polarization values (P) for Lorentz and Lorentz theory, and (PV) for

Vogel’s theory, for many typical groups present in polyimide structures were calculated

and given in Tables 20 through 22. Additional values of the ‘molar polarization’ of

various organic chemical structural groups for ‘additive group contributions’ method can

be found in literature [38] for the calculation of ‘additive group contributions’.

3.5.12.2.2.4. Importance of pre-estimation of dielectric constant value of polyimides

With the help of the molar polarization values given in Tables 20-22, and the application

of Lorentz and Lorentz’s equation (10) and Vogel’s equation (11), and Vora-Wang

equations (13) and 14), one can calculate the estimated values of dielectric constants for

various polyimides and copolyimides well before their synthesis, if the structural units

are known. It will help identifying low-k polyimide’s chemical structures well in

advance. It would open up possibilities of identifying new monomers and synthesizing

and developing numerous low k polyimides for microelectronic, etc. applications.

3.5.13. Morphology The X-ray diffraction patterns of a series of [6FDA + (n mole%) p-SED + (m mole%)

BDAF] fluoro-poly(ether imide) polymer solids are shown in Figure 38. These fluoro-

R2 = 0.9982

2.8

2.85

2.9

2.95

3

3.05

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

% Fluorine Content

Diele

ctric

Con

stant Series1

Poly. (Series1)

[6FDA + p-SED] [6FDA + 75 m% p-SED+25m% BDAF]

[6FDA + 25 m% p-SED+25 m% BDAF]

[6FDA + BDAF]


R2 = 0.9982

2.8

2.85

2.9

2.95

3

3.05

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

% Fluorine Content

Diele

ctric

Con

stant Series1

Poly. (Series1)

[6FDA + p-SED] [6FDA + 75 m% p-SED+25m% BDAF]


[6FDA + BDAF]


224

Table-20 : Group contributions to molar dielectric polarization (P) of typical ‘Phthalimide’, ‘pyromellitimide’ and ‘di Phthalimide’ moieties present in polyimides

CO

NCO

CO

NCO

CO

NCO

CO

NCO

C

CO

O

N

C

O

CO

NCO

CO

NCO

O CO

NCO

CO

NCO

C

O

NCO

C

O

NCO

C

O

NC

O

CCF3

CF3

51.28 276.59

76.845 428.02

102.56 553.18

112.56 618.18

107.76 583.18

121.1 752.38

Group PLL PV Group PLL PV

S

C

O

NCO

C

O

NC

O

O

O

C

O

NCO

C

O

NCO

CCH3

CH3

C

O

NCO

116.43 614.9

120.96 673.18

Where X =

110.56 613.18

136.28 720.74

156.14 8126.58

X C

O

NC

OC

O

NCO

-s-CCH3

C

CO

NCO

CO

NCO

CO

NCO

CO

NCO

C

CO

O

N

C

O

CO

NCO

CO

NCO

O CO

NCO

CO

NCO

C

O

NCO

C

O

NCO

C

O

NC

O

CCF3

CF3

51.28 276.59

76.845 428.02

102.56 553.18

112.56 618.18

107.76 583.18

121.1 752.38


S

C

O

NCO

C

O

NC

O

O

O

C

O

NCO

C

O

NCO

CCH3

CH3

C

O

NCO

116.43 614.9

120.96 673.18

Where X =

110.56 613.18

136.28 720.74

156.14 8126.58

X C

O

NC

OC

O

NCO

-s-CCH3

C

CO

NCO

CO

NCO

CO

NCO

CO

NCO

C

CO

O

N

C

O

CO

NCO

CO

NCO

O CO

NCO

CO

NCO

C

O

NCO

C

O

NCO

C

O

NC

O

CCF3

CF3

51.28 276.59

76.845 428.02

102.56 553.18

112.56 618.18

107.76 583.18

121.1 752.38


S

C

O

NCO

C

O

NC

O

O

O

C

O

NCO

C

O

NCO

CCH3

CH3

C

O

NCO

116.43 614.9

120.96 673.18

Where X =

110.56 613.18

136.28 720.74

156.14 8126.58

X C

O

NC

OC

O

NCO

-s-CCH3

C

224

225

Table-21 : Group contributions to molar dielectric polarization (P) of typical diether diamine moieties present in poly(ether imide)s

O X OWhere X = Di-ether Diamine

a Bond 110.40 574.40

-O- 115.60 604.40

-S- 118.40 634.40

-SO2- 128.80 694.40

Group PLL PV

-CH2- 115.05 595.04

-C(CH3)2- 124.26 636.12

-CO- 120.40 639.40

-C(CF3)2- 128.94 773.60

Group PLL PV


a Bond 110.40 574.40

-O- 115.60 604.40

-S- 118.40 634.40

-SO2- 128.80 694.40

Group PLL PV

-CH2- 115.05 595.04

-C(CH3)2- 124.26 636.12

-CO- 120.40 639.40

-C(CF3)2- 128.94 773.60

Group PLL PV


a Bond 110.40 574.40

-O- 115.60 604.40

-S- 118.40 634.40

-SO2- 128.80 694.40

Group PLL PV

a Bond 110.40 574.40

-O- 115.60 604.40

-S- 118.40 634.40

-SO2- 128.80 694.40

Group PLL PV

-CH2- 115.05 595.04

-C(CH3)2- 124.26 636.12

-CO- 120.40 639.40

-C(CF3)2- 128.94 773.60

Group PLL PV

-CH2- 115.05 595.04

-C(CH3)2- 124.26 636.12

-CO- 120.40 639.40

-C(CF3)2- 128.94 773.60

Group PLL PV

225

226

Table-22 : Group contributions to molar dielectric polarization (P) of typical diamine moieties present in polyimides * : Ref. [38]

68.40 377.20

68.54 456.40

86.60 493.50

84.26 424.76

103.58 530.60

61.28 292.52

25.00 128.60

25.00 128.60

50.00 257.20

50.00 257.20

55.20 287.20

63.86 318.92

54.65 277.84

58.00 317.20

O

C

O

CH

H

S

Group PLL PV

S

O

O

CCF3

CCH3

C

H3C

CH3

CCF3

CF3

Group PLL PV

*

*

68.40 377.20

68.54 456.40

86.60 493.50

84.26 424.76

103.58 530.60

61.28 292.52

25.00 128.60

25.00 128.60

50.00 257.20

50.00 257.20

55.20 287.20

63.86 318.92

54.65 277.84

58.00 317.20

O

C

O

CH

H

S

Group PLL PV

25.00 128.60

25.00 128.60

50.00 257.20

50.00 257.20

55.20 287.20

63.86 318.92

54.65 277.84

58.00 317.20

O

C

O

CH

H

S

Group PLL PV

S

O

O

CCF3

CCH3

C

H3C

CH3

CCF3

CF3

Group PLL PV

S

O

O

CCF3

CCH3

C

H3C

CH3

CCF3

CF3

Group PLL PV

*

*

226

227

poly(ether imide) and fluoro-copoly(ether imide)s were amorphous as indicated by broad

halo patterns without any significant or obvious X-ray diffraction peaks typically found

in crystalline polymers in the XRD spectral window range from 2θ = 10° to 2θ = 30°.

Figure-38 : X-ray diffraction patterns of fluoro-copoly(ether imide)s series [6FDA + (n mole %) p-SED + (m mole %) BDAF] The result was consistent with that of the solubility behavior of these polymers and

also their glass transition temperature (Tg) result by DSC. This could be explained in

terms of the presence of 'spacer' link, such as ‘sulfonyl’ (-SO2-), isopropylidene’ (-C-

(CH3)2-), and ‘hexafluoroisopropylidene’(-C-(CF3)2-) group in the fluoro-poly(ether

imide) and fluoro-copoly(ether imide)s. The 'spacer' link reduces the rigidity of the

polymer chain, which inhibits its packing [70-71]. The d-spacing and (Tg) values were

4.72Å (Tg = 293°C), 5.08Å (Tg=259°C) and 5.48Å (Tg = 267°C) respectively in the case

of fluoro-poly(ether imide)s [6FDA + p-SED], [6FDA + BPADE] and [6FDA + BDAF],

which are all made from para isomers of 'ether' containing diamine monomer. Where as

the Tg of copolymers lies in between these values.

An increase in d spacing was observed when the bulkier group -C(CF3)2- was

substituted for -C(CH3)2- in the structure of the diamine moiety of the of [6FDA +

BPADE] poly(ether imide) polymer chain segment. The increased inhibition of the

0

50

100

150

200

250

300

350

10 15 20 25 30 35 40 45 502 Theta

Inte

nsity

6FDA + pSED

6FDA + 0.75 pSED + 0.25 BDAF

6FDA + 0.5 pSED + 0.5 BDAF

6FDA + 0.25 pSED + 0.75 BDAF

6FDA + BDAF

228

conformational rotation is also reflected in a slight increase in Tg values of [6FDA +

BDAF] with Tg =267°C as compared to [6FDA + BPADE] with Tg =259°C. Similarly,

ULTEM®1000 (d spacing = 5.24Å and Tg = 218°C) was also found to be completely

amorphous.

3.6. CONCLUSION

Two series of high temperature stable fluoro-copoly(ether imide)s were successfully

synthesized by solution polymerization. The FT-IR study confirmed that fluoro-

copoly(ether amic acid) was successfully converted to fluoro-copoly(ether imide) by the

chemical imidization method. The solid fluoro-poly(ether imide)s and fluoro-

copoly(ether imide)s based on 6FDA were soluble in almost all the organic solvents

tested in this study at room temperature. Films of fluoro-poly(ether imide)s [6FDA + p-

SED], and [6FDA + BDAF] were almost colorless. The moisture absorptions of fluoro-

copoly(ether imide) films were found to be in the range of 0.5 to 1.05%, which was

significantly lower than the ULTEM1000 (1.52) and KaptonH (3.0) at 100 RH at

50°C.

The fluoro-poly(ether imide)s were amorphous as determined from XRD

measurements. This activation energy for the thermal degradation in kinetic study

suggested that BDAF based fluoro-copoly(ether imide)s have better stability than

BPADE based polymers. This observation was also confirmed by the thermo-oxidative

stability (TOS) study. Also these polymers have very good TOS than ULTEM1000 and

KaptonH. The glass transition temperatures (Tg) both series of l fluoro-copoly(ether

imide)s were in excess of 240oC and well above the Tg of ULTEM1000. The Tg values

of fluoro-poly(ether imide)s decreased in the following order in terms of the spacer link

present in the polymer: (-SO2-) > (-C-(CF3)2-) > (-C-(CH3)2-). Whereas for the

copoly(ether imide)s, the Tg lies in between this values. These polymers could be

229

processed readily into thin film and shaped articles via conventional processing

technique. It was demonstrated that the glass transition temperature (Tg) and dielectric

constants (ε') of poly(ether imide)s also could be tailored by controlling the rigidity of

the chain through the introduction of rigid or flexible “separator" groups. [80, 85-86, 89,

92-94, 110-111].

The dielectric constant of the non-fluorinated polyimide: [ODPA + m-Tolidine],

KaptonH and [PMDA + 3,3-ODA] at lower frequency was found to be higher than that

at the high frequency. The rigid polyimide has a higher dielectric constant at low

temperature and low frequency.

The fluorine-containing polyimide shows a lower dielectric constant (ε'). The

dielectric constant of the fluorine-containing polyimide decreases with increasing

fluorine content in polymer. The dielectric constant also decreases with increasing

frequency. Fluorine containing aromatic polyimides have lower dielectric constants at

high temperature and low frequency, indicating a better temperature dependence

dielectric insulation properties than KaptonH, and [PMDA + 3,3-ODA] and

UPILEXS.

The molar polarization PLL and PV values of the ‘Phthalimide’ and ‘Pyromellitimide’

groups present in polyimides have been derived and their usefulness have been

established. For the ‘Phthalimide’ group, the PLL and PV values are 51.28 and 276.59,

respectively. Whereas for the Pyromellitimide’ they are 76.85 and 428.02, respectively.

These values can be used in the estimation of the dielectric constants of polyimides

having such groups. Using these values we found that the estimated dielectric constant

values for ULTEM-1000, SIXEF-44 and other commercial and literature reported

polyimides were in good agreement with the experimental as well as literature reported

values.

230

It was also now well established that the dielectric constant of copolyimide does not

have the simple additivity of the dielectric constant values of its individual

homopolymeric components. The dielectric constants of copolymers can only be

estimated by the use of Vora-Wang equations and substituting the values of polarization

PLL and PV, volume V, molecular weight M, of the individual homopolymeric

components through the group contribution additivity. The Vora-Wang equations can be

used for any copolyimides or copolymers having two or more co-monomer molecules in

its chemical structural repeat units. Similarly, the molar polarization PLL and PV values of

‘Phthalimide’ and ‘Pyromellitimide’ and other groups typically found in polyimides, as

given in this Chapter as well as found in literature, and the application of Lorentz and

Lorenz’s theory equation (10), Vogel’s theory (11) and Vora-Wang equations (13) and

(14), would help to estimate the dielectric constant values of for various polyimides and

copolyimides and other such polymers well before their actual synthesis, if the chemical

structure and composition of their repeat units are known [48, 111]. The dielectric

constant by estimation method and the result given in this paper would provide practical

guidelines, open up possibilities for designing and identifying, and developing numerous

newer polyimides structures with predetermined low dielectric constant.

Partially fluorinated poly(ether imide) [6FDA + p-SED] has been identified as low-K

polymer for further studies and development for ideal microelectronic applications such

as high temperature interlayer insulators and dielectrics for micro-electronic packaging,

coating and adhesive as well as substrates for electronic flex circuit, matrices for high

performance composites for aerospace and advanced aircraft, and materials for gas

separation membranes.

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97. S. Yoshida, A. S. Hay, Macromolecules, 30 (1997) 5979.

98. R. Yokota, in “Photosensitive Polyimides-Fundamental and Applications”, K. Horie,

T. Yamashita (Eds.), Technology Publishing Co. Lancaster 1995, p. 49.

99. R. M. Ikeda, J. Polym. Sci., 34 (1966) 353.

100. D. Jiles, “Introduction to the Electronic Properties of Materials”, Chapman &

Hall, London 1994.

101. J. R. Fried, “Polymer Science and Technology”, Prentice Hall, Inc. Upper Saddle,

NJ, (1995) p 208

102. S. X. Chen, T.S. Chung, R. Wang, R. H. Vora, “Gas sorption properties of

6FDA-Durene/1,4-phenylenediamie (pPDA) and 6FDA-Durene/1,3-

phenylenediamine (mPDA) copolyimides”, Communicated to J. Appl.. Polym. Sci.

(2002).

103. K. R. Carter, R. A. DiPietro, M. I. Sanchez, T. P. Russell, P. Lakshmanan, J. E.,

McGrath, Chem. Mater., 9 (1997) 105.

104. T. Sawada, A. Ando, Chem. Mater., 10 (1998) 3368.

105. K. R. Carter, R. A. DiPietro, M. I .Sanchez. S. A. Swanson, Chem. Mater., 13

(2001) 213.

106. S. J. Martin, J. P. Godschalx, M. E. Mills, E. O. Shaffer (II), P. H. Townsend,

Adv. Mater. 12 (2000) 1769.

107. F. E. Karasz, (Ed.) Dielectric properties of Polymers, Plenum Press, New York,

1972.

108. J. C. Maxwell, Phil. Mag., 32 (1866) 390.

109. J. C Maxwell-Garnett, Philos., Trans. R. Soc. London, 205 (1906) 237.

110. J. Monk, D. A. Soane, in Polymers for Electronics and Photonic Applications, C.

P. Wong (Ed.), Academic Press, Inc. Boston (1993), p. 146.

111. R. H. Vora, P. S. G. Krishnan, S. H. Goh, T.-S. Chung., Adv. Funct. Mater, 11(5)

(2001) 361.

237

CHAPTER-4

PREPARATION AND CHARACTERIZATION OF 4,4-BIS(4-

AMINOPHENOXY) DIPHENYL SULFONE BASED [FLUORO-

POLY(ETHER IMIDE) /ORGANO-MODIFIED CLAY]

NANOCOMPOSITES

238

4.1. INTRODUCTION

4.1.1. Research Background

Polyimides are versatile engineering polymers having reasonably good mechanical

properties, chemical resistance, low dielectric constant and thermal stability. They are

therefore prominent polymers amongst high performance high temperature stable organic

materials. [1] However, the search for new polyimides or their hybrids with other organic

or inorganic materials which would provide improved processability and higher glass

transition temperatures (Tg) with desired mechanical properties than the commercially

available polymers has received significant ongoing attention from both academia and

industries.

In the last fifteen years, natural clay-polymer nanocomposites have become an active

field of research because of their unique microstructures and enhanced properties. As of

December 2001, Chemical Abstract [2] search revealed 270 publications and 56 patents

published in this emerging field of R&D. It is expected that organic polymer/inorganic

hybrid or nanocomposites materials (Ceramers [3]) would exhibit a unique characteristic

and properties of combination of both ceramics, (viz. retention of mechanical properties

at high temperature, low thermal expansion), as well as organic polymers (viz.

toughness, ductility, and processebility) [3]. Presently, no such perfect ‘Ceramer’

materials with all the desired properties, based on ‘polyimides’ chemistry have been

developed or marketed yet. However, it is expected, that, if developed, these new

materials would provide unique properties for potential applications for electronics

(molding compounds, thermally stable alpha particle shielding film), industrial and

aerospace (stronger light weight, and high temperature stable structural components, as

well as abrasion materials), life science (bio-materials for medical device and sensors), or

substrate materials to grow bio - enzymes or proteins molecules, separation membranes,

239

MEMs, etc., industries.

In the development of such polymer/clay nanocomposites, it is clearly understood that

structural rigidity of dianhydrides contributes to the increase in the glass transition

temperatures of those polyimides in the range of 300 to 400°C. However, there are no

suitable processing methods available to process such high Tg materials. Due to these

limitations many researchers focused their research on the modification of the backbone

structures of polyimides and/or molecular level incorporation of inorganic clay to form

nanocomposites. Their approach such as the incorporation of a flexible ether linkage and

meta oriented phenylene rings into polymer backbone led to an increase in polymer chain

flexibility and solubility of neat polyimides, but at the same time lowered the effective

upper use temperature of these polymers [3-9], making them rather unqualified for the

ever increasing demand for higher upper use temperature materials for microelectronics

applications. Similarly, the incorporation of inorganic clay leads to high thermal stability

but at the expense of fracture toughness and mechanical properties. In the past it was

shown that the incorporation of fluorine-containing monomers would increase the

thermo-oxidative stability (TOS) and lower dielectric constant as well as moisture

absorption in the polyimide polymers. [10-16]. However, low dielectric constant, high

performance fluoro-polyimides, such as SIXEF PI from Hoechst Celanese Corp.

generally were expensive [13-15].

It is a common understanding that for some niche electronic applications the high cost

may not be the determining factor. In fact, premium performance dictates premium price.

Desired performance and stability of a given polyimide at higher temperature processing

conditions, imparting with specific electrical and thermo mechanical properties, may

justify its higher price [16].

240

4.1.2. Research objectives:

The third objective of my research was to synthesize and characterize fluoro-

poly(ether imide) polymers and its inorganic compound based nanocomposites materials.

The research also dealt with the study their structure property relationship in terms of

their key properties such as thermal stability and thermal degradation kinetics,

mechanical, and surface properties, as well as hydrolytic stabilities.

To meet the objectives of the present study, efforts were focused on the synthesis and

study of high-performance fluoro-poly(ether imide)/inorganic clay nanocomposites from

commercially available monomers and high purity fine powered Na-Montmorillonite

clay. One fluoro-poly(ether imide) polymer [6FDA + p-SED] based on 2,2-bis(3,4-

dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 4,4’-bis(4-

aminophenoxy)diphenyl sulfone (p-SED), was selected because this polymer as

discussed in Chapter 2 is a thermoplastic with high Tg, good thermal stability, excellent

thermo-oxidative stability (TOS) at 315°C over 300 hours, low moisture pick-up , along

with a low dielectric constant (ε′ <2.8). The thermal, hydrolytic stability and dielectric

properties of [6FDA + p-SED] fluoro-poly(ether imide) (6F-PEI) polymer [16] are

summarized in Table 1.

Table-1 : properties of [6FDA + p-SED] fluoro-poly(ether imide) (6F-PEI) polymer

TGA 5%

Weight Loss (°C)

Fluoro (ether-imide) Polymer Composition

DSC Tg

(°C)

In Air In N2

Char yield in N2

@ 850°C (%)

TOS Weight

Loss @ 315°C for 300hr

(%)

Moisture Absorption @ 55°C and 100% RH

(%)

Dielectric Constant

(ε′) @ 10MHz

[6FDA + p-SED]

293

544

561

52

2.74

0.5

2.74

A series of 6F-PEAA/montmorillonite (MMT) clay] nanocomposites formulations

having a varying percent of p-SED treated MMT clay (i.e., Organo-soluble clay) were

synthesized, and from which the [(6F-PEI) / MMT clay] nanocomposites films were

241

fabricated and systematically characterized.

The solubility, morphology, thermal, thermo-oxidative stability, thermo-mechanical,

moisture absorption, mechanical and surface properties of few selected [(6F-PEI)/MMT

clay] nanocomposite films were studied. The Coats and Redfern equation [17] was used

for the evaluation of the thermal stability, and their activation energies for thermal

degradation were calculated. The results of this research work are reported and discussed

in this chapter.

4.2. EXPERIMENTAL

4.2.1. Materials Kunipia F has a smaller grain size than 200 mesh (< 74 µm). Electronic grade 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)

was received from Chriskev, Co. Inc, KS, USA; 4,4-bis(4-aminophenoxy)diphenyl

sulfone (p-SED), was received from Wakayama Seika Kogyo Co. Ltd., Japan. Acetone,

NMP, tetrahydrofuran (THF), N,N-dimethylacetamide (DMAc), N,N-dimethyformamide

(DMF), dimethylsulfoxide (DMSO), γ-butyrolactone (BLO), methylene chloride,

formamide, fuming sulfuric acid, 36% conc. hydrochloric acid, silver nitrate, all received

from Sigma–Aldrich, except NPM all others were used as received. Kunupia F clay (Na-

Montmorillonite, grain size <200 mesh (<74 µm)] obtained from Kunimine Industries

Co., Ltd. Japan. ULTEM1000 pellets were obtained from General Electric, USA and its

films were prepared by solution casting method. KaptonH film of 25µm thickness was

obtained from Du Pont, USA. NMP was always freshly distilled over P2O5 under

reduced pressure and stored over pre-dried molecular sieves and used when needed.

4.2.2. Synthesis

4.2.2.1. Preparation of p-SED (diamine) modified MMT clay

There are several methods reported in the literature, [18-23] on how hydrophilic pure

Na - montmorillonite clay could be treated to make it hydrophobic and more compatible

242

Figure-1 : Synthesis scheme for p-SED modified MMT clay, [6FDA + p-SED] fluoro-poly(ether amic acid), and [6FDA + p-SED]/MMT clay nanocomposites pre-formulations

Charge p-SED + NMP solvent under Argon atmosphere

Apply agitation at room temp.

Dissolve diamine to get clear solution

Continue agitation

Add 6FDA into solution

Apply agitation for overnight at room temperature

[6FDA + Diamine] Fluoro-poly (ether amic acid) (6F-PEAA) obtained

p-SED + Hydrochloric acid + distilled water

Stirred for 1 hour

Add Na-Montmorillonite clay for ion exchange

reaction

Stirred overnight at 60ºC

Washing & filtering of the ion exchanged clay with

distilled water

Filtrate tested with Silver Nitrate solution (AgNO3) for

presence of chloride ion

White precipitate formed?

No Yes

Clay dried in vacuum oven at 80ºC overnight

Ground the dried p-SED modified Organosoluble

MMT clay

Prepare 5 OrganosolubleMMT clay suspension in

NMP solvent (1%,2.5%,5%,10% & 15%)

Apply agitation overnight

Fluoro-poly (ether amic acid) added to the 5 solutions prepared

Viscous [Fluoro-poly (ether amic acid)/MMT clay] Nanocomposite Pre-formulation obtained after applied agitation for overnight at room temp.

Preparation of Fluoro-poly (ether amic acid) Preparation of p-SED Diamine Modified MMT Clay

Filter the clay with 180 micrometer mesh sieve

Charge p-SED + NMP solvent under Argon atmosphere

Apply agitation at room temp.

Dissolve diamine to get clear solution

Continue agitation

Add 6FDA into solution

Apply agitation for overnight at room temperature

[6FDA + Diamine] Fluoro-poly (ether amic acid) (6F-PEAA) obtained

p-SED + Hydrochloric acid + distilled water

Stirred for 1 hour

Add Na-Montmorillonite clay for ion exchange

reaction

Stirred overnight at 60ºC

Washing & filtering of the ion exchanged clay with

distilled water

Filtrate tested with Silver Nitrate solution (AgNO3) for

presence of chloride ion

White precipitate formed?

No Yes

Clay dried in vacuum oven at 80ºC overnight

Ground the dried p-SED modified Organosoluble

MMT clay

Prepare 5 OrganosolubleMMT clay suspension in

NMP solvent (1%,2.5%,5%,10% & 15%)

Apply agitation overnight

Fluoro-poly (ether amic acid) added to the 5 solutions prepared

Viscous [Fluoro-poly (ether amic acid)/MMT clay] Nanocomposite Pre-formulation obtained after applied agitation for overnight at room temp.

Preparation of Fluoro-poly (ether amic acid) Preparation of p-SED Diamine Modified MMT Clay

Filter the clay with 180 micrometer mesh sieve

243

with hydrophobic precursor of polyimide polymer. The Na ions of hydrophilic of MMT

clay surface should be exchanged by organic cations through ion exchange process to

provide hydrophobic environment within the treated clay galleries thereby rendering the

surface hydrophobic. This allows to accommodate the hydrophobic poly(amic acid) [19].

We have modified the procedure reported by Tyan and co-workers [24] and shown as

synthesis scheme in Figure 1, and used in this investigation.

4.2.2.1.1. Procedure of making p-SED (diamine) modified MMT clay

10g of 325-mesh screened Kunipia F (Na-montmorillonite) clay with cationic

exchange capacity of 74meq/100g was dissolved in the p-SED/HCl solution prepared by

dissolving 1.60g of p-SED in 1000 mL of 0.01N HCl and heating at 30-35°C for 1 hour.

This reaction mixture was further heated and maintained at 60°C with vigorous agitation

overnights. The mass was cooled down to 40°C and vacuum filtered. The solid wet cake

of p-SED diamine treated MMT was washed with deionised water in a large beaker with

rapid stirring for 1 hour. The slurry was filtered again and the mother liquor was titrated

against 0.1N AgNO3 to check of removal of Cl− ions as white precipitation of AgCl. The

washing step was repeated several times until total removal of Cl− ions. The cake was

given a final wash and after filtration it was dried in a vacuum oven at 80°C for 24 hours.

p-SED ion exchanged on MMT clay was calculated to be ~25% based on the total

charges on MMT layer. Dry solid p-SED treated MMT (diamine modified MMT) was

ground into fine powder and screened with a 325-mesh (180mm) sieve, and stored in PP

bottles under argon environment for further use in the preparation of (6F-PEAA)/diamine

modified MMT clay nanocomposites formulations.

4.2.2.1.2. Synthesis of fluoro-poly(ether amic acid)

To prepare (6F-PEAA)/diamine modified MMT clay nanocomposites formulations

having various weight % of modified MMT, first a big master batch of [6FDA + p-SED]

244

fluoro-poly(ether amic acid) was synthesized from the monomers 6FDA and p-SED

whose chemical structures are shown in Figure 2.

Figure-2 : Structure of 6FDA and p-SED 4.2.2.1.2.1. Master batch of fluoro-poly(ether amic acid) (6F-PEAA)

Several procedures for the preparation of polyimides have been reported in the

literature [25-39]. The most common procedure used in this investigation is a simplified

one-pot-two-step polymerization process [40] as shown in the Figure 3.

O

C C

CCF3

O

O

O

C C

CCF3

O

O

OH

C C

CCF3

O

O

N

+

n

n

[6FDA + p-SED] Fluoro-poly(ether amic acid) [6F-PEAA] Solution


POLYMERIZATION

6FDA p-SED (Diether linked diamine)

Step wise Curing byHeating to temp >300oC( -2H2O & NMP )

THERMAL IMIDIZATION

[6FDA + p-SED] Fluoro-poly(ether imide) [6F-PEI] polymer

CF3

CF3

CF3

C

C

O

O

N

C

C

O

O

O

C

C

O

O

HO

HN

HN

S OH2N NH2

O S O

O S O

O

O

O

O

O

O

Figure-3 : Synthesis of [6FDA + p-SED] (6F-PEAA) and [6FDA + p-SED] (6F-PEI) 4.2.2.1.2.1.1. Synthesis Procedure The polymerization was carried out until completion of only 1st step shown in reaction

scheme in Figure 3. [6FDA + p-SED] fluoro-poly(ether amic acid) (6F-PEAA) was

successfully synthesized from 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane

dianhydride (6FDA) and 4,4-bis(4-aminophenoxy) diphenyl sulfone (p-SED), as follows.

OO NH2NH2

OSO

4,4'-Bis (4-aminophenoxy) diphenyl sulfone [p-SED]

6FDA

CCF3

CF3

C

C

C

C

O

O

O

O

O O

245

The second, thermal imidization step was used only to convert wet (6F-PEAA) film into

dry (6F-PEI) film as discussed later.

Accurately weighed 0.09 mole (39.978g) of solid 6FDA was added in small increment

over a period of 1 hour to 0.0882 mole (38.1465g) of p-SED diamine pre-dissolved in

freshly distilled NMP to make 25% solid concentrations under an argon atmosphere. The

reaction mixture was then stirred under nitrogen at room temperature for overnight to

produce a master batch of (6F-PEAA) solution, which was stored in a refrigerator before

the preparation of [(6F-PEAA)/MMT clay] nanocomposites formulation. A small sample

of (6F-PEAA) was also withdrawn and precipitated with deionized water, washed

repeatedly with fresh DI water, and dried at room temperature for 48 hours overnight in

an air-circulating oven, and then stored in desiccator for later analysis.

4.2.2.1.3. Preparation of p-SED treated MMT clay suspensions in NMP

The amount of p-SED treated MMT clay needed to charge was calculated based on the

solid content of (6F-PEAA) to achieve 1%, 2.5%, 5%, 10% and 15% clay level in

respective nanocomposite formulations. Five suspensions were prepared with the

following amount of p-SED treated MMT clay in NMP and stirred vigorously overnight.

1. 0.130 g p-SED diamine treated MMT + 13.021g NMP





4.2.2.1.4. Preparation of fluoro-poly(ether amic acid)/MMT clay nanocomposites pre-formulation

The master batch of [6FDA + p-SED] fluoro-poly(ether amic acid) (6F-PEAA) was

divided in to 6 equal parts of 52.00g each, and each part was mixed separately with the

above listed suspensions having various level of p-SED diamine treated MMT clay.

246

After vigorous stirring overnight (Figure 1) to achieve an overall exfoliation of p-SED

modified MMT clay in base [6FDA + p-SED] fluoro-poly(ether amic acid) as shown in

Figure 4 [41], diluted [(6F-PEAA)/MMT clay] nanocomposites pre-formulation was

obtained having 1%, 2.5%, 5%, 10% and 15% clay level respectively. It must be noted

here that the clay galleries at a higher clay content could not always be effectively

exfoliated into nanolayers and some may remained as aggregates which reduce the

clarity of formulation in visible light. Therefore the solid content of (6F-PEAA) was

reduced to about 20% during formulation preparation as evident from the suspension

preparation above

Figure-4 : Schematic drawing of (a) ion exchanged MMT clay with p-SED (i.e., modified MMT clay) and (b) dispersion of p-SED modified MMT clay in the poly(ether amic acid) in [(6F-PEAA)/MMT clay] nanocomposite formulations [41]. Formulations with up to 5% MMT clay were very clear and transparent amber color

liquids. But with increasing clay content the remaining formulations were translucent

dark amber color liquids. These formulations were then used in casting wet films to get

[(6F-PEI)/MMT clay] nanocomposites by thermal imidization. The samples of these

formulations were used to determine bulk viscosity, inherent viscosity and molecular

weights. The rest of unused portions were stored in a refrigerator.

4.3. FABRICATION

4.3.1. [6FDA + p-SED] Fluoro-poly(ether imide), and [6FDA + p-SED]/MMT clay nanocomposite film preparation

There are a number of commercial film products produced by solvent casting method

(a) (b)

S

O

OO

N+

H2NO

S

O O

ON+

NH2

O

S

O

O

O

N+

NH2

O

= S

O

OON+ NH2

O

S

O

OO

N+

H2NO

S

O O

ON+

NH2

O

S

O

O

O

N+

NH2

O

= S

O

OON+ NH2

O

S

O

OO

N+

H2NO

S

O O

ON+

NH2

O

S

O

O

O

N+

NH2

O

S

O

OO

N+

H2NO

S

O O

ON+

NH2

O

S

O

O

O

N+

NH2

O

= S

O

OON+ NH2

O= S

O

OON+ NH2

O

247

with a fairly wide variety of applications ranging from electrical, electronics, solar films

and adhesive coated tapes for automobile trim etc [42]. For many polymeric materials

which are not melt processable but soluble in organic solvents, such as in the case of

many polyimides, solvent casting is the only way to prepare polymer film.

Solutions of 6F-PEI and ULTEM1000 were made at 15% solid concentration level in

NMP and filtered through a 0.5µm filter under nitrogen pressure. These filtered solutions

and [(6F-PEAA)/MMT clay] nanocomposites pre-formulations were then coated onto

glass plates using a doctor blade (Gardner Film Casting Knife, Model AG-4300, Pacific

Scientific, USA) with adjustable gate clearance controlled with Micrometer from 0 to

6250 µm gap.

Figure-5 : Film preparation and thermal curing program The films were dried in a nitrogen environment for an hour and then heated gradually

according to the thermal heating cycle shown in Figure 5 in a Lenton Thermal Design,


80°C

110°C150°C

150°C

110°C

200°C

200°C

250°C

250°C

1 HR

1 HR

1 HR



1 HR1 HR

1 HR1 HR

RT55°C

55°C

300°C

300°C


80°C

110°C150°C

150°C

110°C

200°C

200°C

250°C

250°C

1 HR

1 HR

1 HR



1 HR1 HR

1 HR1 HR

RT55°C

55°C

300°C

300°C

Preparation of Film on Glass Plate Stepwise heating of film in ovenPreparation of Film on Glass Plate Stepwise heating of film in oven

248

UK, programmable oven up to 250oC stepwise and held at 300oC for 1 hour each.

During these heating steps, thermal imidization also took place, which converted 6F-

PEAA to 6F-PEI as shown in Figure 3. After heating, the films were allowed to cool

down gradually to room temperature. Films of (6F-PEI) were almost colorless and

ULTEM1000 film was yellow to amber in color. [(6F-PEI)/MMT clay] nanocomposite

films were dark brown to black in color as the clay content increased. The self-

supporting films were lifted up from the glass plate by soaking in water for 5 to 10

minutes, and dried with a paper towel and further dried in an oven at 150oC for 30

minutes. The film thickness was measured by Electronic Digimatic Thickness Gage

(model 547-400) from Mitutoyo (Japan) having measuring range of 1-125mm /or 0-

12500µm with a resolution of 0.001mm /or 1.25µm, and a measuring accuracy of ±

0.002mm /or ± 2.5µm. The film thickness was determined as the average of 5 readings

on each film sample. Films of nanocomposites from 20 to 35µm thick were obtained.

The films of KaptonH (25µm), and ULTEM1000 (25µm) were used as 'the control'.

Before the characterization was performed, the films were re-dried in the vacuum oven

overnight at 80oC to remove any moisture absorbed in the film, and then put into the

desiccator.


Most methodologies of characterization techniques used in this work were discussed

in respective section of Chapters 1, 2 and 3.


4.4.1.1. Inherent viscosity

The inherent viscosity of [6FDA + p-SED] fluoro-poly(ether amic acid) (6F-PEAA)

was determined using a Schott-Gerate Viscometer at 25°C.:

249

4.4.1.2. Bulk Viscosity

The bulk viscosities of 6F-PAA was determined at room temperature (25°C) a fixed

shear rate (5 rpm) using Brookfield Programmable Rheometer Model DV-III (with

Rheocalc software and Brookfield constant temperature water bath model TC-200/500)

and CP42 spindle. About 1mL of bubble free sample was used. Prior to analysis, sample

was allowed to reach equilibrium for 1 minute before taking reading. Readings were

automatically recorded by the Rheocalc software. Average of 6 readings was taken for

viscosity calculation.

4.4.2. Fourier transform-IR spectroscopy (FT-IR) FT-IR spectra of the poly(ether-amic acid) (6F-PEAA) solid and [(6F-PEI)/MMT

clay] nanocomposites films were obtained using Perkin Elmer FTIR.

4.4.3. Gel permeation chromatography (GPC)

The molecular weights of (6F-PAA), and [(6F-PEAA)/MMT clay] nanocomposite

formulation samples were determined using a Waters GPC system.

4.3.4. X-ray diffraction (XRD) Wide-angle X-ray diffraction (WAXD) measurement of compressed disks of average

thickness 1mm of solid (6F-PEI), [(6F-PEI)/MMT clay] nanocomposite and

ULTEM1000, were carried out on an X-ray diffraction unit (Phillips model PW 1729-

10) fitted with Cu - Kα radiation (30 kV, 20 mA) with wavelength λ of 1.54Å. The

scanning rate was 0.5°/min. at ambient temperature. The spectral window ranged from

2θ = 1° to 10°, as well as for 2θ from 10° to 30°. The corresponding d-spacing value was

calculated from the diffraction peak maximum, using the Bragg equation:

d = λ/2 sinθ (1)

4.4.5. Solubility of polymer films

The solubility of (6F-PEI), [(6F-PEI)/MMT clay] nanocomposite, ULTEM1000 and

250

KaptonH films was determined by dipping 1x1cm square film samples in capped vials

containing selected solvents and kept on (IKIA Laboratechnik horizontal shaker Model

No. K3501 (digital) at room temperature. The samples were visually checked after 24

hours, and the observation on level of solubility was recorded.

4.4.6. Hydrolytic stability Moisture absorption by the thin films (6F-PEI) and [(6F-PEI)/MMT clay]

nanocomposite, ULTEM1000 and KaptonH was determined by calculating the

difference in weight of pre-dried and wet films after soaking them in Di-water at 55°C

for 100 hours.

4.4.7. Differential scanning calorimetry (DSC)

Glass transition temperatures (Tg) of (6F-PEI), and [(6F-PEI)/MMT clay]

nanocomposite, ULTEM1000 and KaptonH films were determined from the second

heating cycle using differential scanning calorimeter (DSC) at a heating rate of 10oC/min

in flowing nitrogen condition.

4.4.8. Thermogravimetric analysis (TGA) Thermal decomposition temperatures (5% wt. loss) of (6F-PEI), and [(6F-PEI)/MMT

clay] nanocomposite films, and also of ULTEM1000 and KaptonH films were

determined using dynamic TGA at a heating rate of 10oC/min in flowing air as well as

nitrogen atmosphere.


Long-term isothermal, thermo-oxidative stability (TOS) study of (6F-PEI) and [(6F-

PEI)/MMT clay] nanocomposites, ULTEM1000 and KaptonH films were performed

on their film samples in air for 300 hours at 300oC (572oF) using Lenton Thermal

Design, UK programmable forced air oven.

251

4.4.10. Dynamic mechanical analysis (DMA) The storage modulus E', tan δ and loss modulus E" of fluoro-poly(ether imide),

nanocomposites films were determined by dynamic mechanical analyzer (DMA) at a

heating rate of 3°C / min. in air at a frequency of 1 Hz and an amplitude of 0.2mm.

4.4.11. Thermomechanical analysis (TMA)

The coefficient of thermal expansion (CTE) values (m/m°C) of (6FPEI) and [(6F-

PEI)/MMT clay] nanocomposites films were determined by thermal mechanical analyzer

(TMA) [model TMA-2940 from TA instruments] at heating rate of 5°C/min in air.

(ASTM method D 696).

4.4.12. Mechanical properties

Mechanical properties of fluoro-polyetherimide (6F-PEI) and [(6FPEI)/MMT clay]

nanocomposites films were determined using Instron Mechanical Analyser Model 5548

using 0.2cm wide and 4.00cm long sample with the clamp distance of 2.00cm.

4.4.13. Surface properties

For surface properties determination, contact angle measurement was carried out by

the Wilhemy method [43] and the advancing and receding contact angles of the films

were measured. An electro balance (Krüss tensiometer model K14 from Krüss, USA)

and a reversible elevator were used to measure the contact angle. A sample film (0.3-

0.6mm in width and 4-5mm in length) was suspended from the arm of an electro balance.

A beaker containing a testing liquid (de-ionized water or formamide) was raised by an

elevator so that liquid surface reached 2-3mm higher than the lower edge of the film

(immersion). Then the beaker was moved down to the original position (emersion). A

continuous weight was recorded during an immersion-emersion cycle at an interfacial

moving rate of 0.3mm/min. This process was repeated thrice and the weight was

recorded to confirm the reproducibility within the statistical deviation. The contact angle

252

was calculated from the wetting force using Wilhelmy equation [43].

4.5. RESULTS AND DISCUSSION 4.5.1. Properties

The properties of [6FDA + p-SED] fluoro-poly(ether imide) (6F-PEI) prepared by the

one-pot, two-step method and polymerization scheme shown in Figures 1 and 3 and the

[(6F-PEI)/MMT clay] nanocomposites prepared therefrom by thermal imidization of the

[(6F-PEAA)/MMT clay] nanocomposites formulations for this study, are listed in Tables

2 through 7. The chemical structures of the repeat units of the [6FDA + p-SED],

ULTEM1000 and KaptonH are shown in Figure 6

Figure-6 : The chemical structures of the repeat units of the [6FDA + p-SED], ULTEM1000 and KaptonH polymers 4.5.1.1. [6FDA + p-SED] fluoro-poly(ether imide)’s chemical structural

characteristics The FTIR spectra of (6F-PEAA) and (6F-PEI) shown in Figure 7 showed their distinct

features, which clearly indicated the imide ring formation and disappearance of the

amide peak during the thermal cyclization step. The characteristic absorption bands of

amides and carboxyl groups in the spectra at 3240 to 3320cm-1and 1500 to 1730cm-1

region disappeared and those of imide ring appeared near 1784 cm-1 (asym. C=O

stretching) and 1728cm-1 (sym. C=O stretching), 1376cm-1 (C-N stretching) 1063cm-1

C

CH3

S

O

O

OC

C

C

C

CF3

O O

O

N

C

O

CN

C

O

O

CN

C

O

O

O O

C

C

C

O O

O

N

C

O

CH3

n

O

CF3

N

n

Nn

O

Kapton-H : [ PMDA + ODA]

ULTEM -1000 : [BPADA + m-PDA]

6F-pSED Fluoro-poly(ether imide) : [ 6FDA + p-SED ]

253

and 744cm-1 imide (ring deformation). Also the aryl-ether absorption band around

1250cm-1 for both amic-acid and imide was very strong indicating stability of the

structure and successful conversion of poly(ether amic acid) to poly(ether-imide).

Figure-7 : FTIR spectra of [6FDA + p-SED] (6F-PEAA) and [6FDA + p-SED] (6F-PEI) 4.5.1.2. Viscosity and Molecular weights The solution properties, i.e., inherent viscosity, bulk viscosity and the molecular

weight data for the master batch of base polymer [6FDA + p-SED] fluoro-poly(ether

amic acid) (6F-PEAA), and the molecular weights of [(6F-PEAA)/MMT clay]

nanocomposites pre-formulations are reported in Table 2.

Table -2 : Solution properties of [6FDA + p-SED] fluoro-poly(ether amic acid) (6F- PEAA) and [(6F-PEAA)/MMT clay] nanocomposites pre-formulations

Viscosity Molecular Weights by GPC

(6F-PEAA)/MMT clay Nanocomposite pre-formulation

with % Clay Contents Inherent (dL/gm)

Bulk (CPa)

Mw Mn d

0 0.57 >12000 47210 21660 2.18 1 29040 13900 2.10

2.5 29250 14995 1.95 5 34890 19150 1.82 10 32772 19125 1.72 15 32615 18990 1.72

CC

C

C

CF3

O O

O

HNC

O

CF3

S OO

O

O

OH

HN

HO

S

O

O

OC

C

C

C

CF3

O O

O

N

CF3

C

O

N On

6F-PEIn

6F-PEAA

Wavenumber (cm-1)1500 50010002000

1545.72

Amide IIC-NH Acid ortho

to AmideC=O (COOH)1714

[6FDA + p-SED] (6F - PEAA)[6FDA + p-SED] (6F - PEI)

%T

725.31C-N Bending1061.07

1250.33

1376.08C-NStretching:Imide

1784.4

725.29


Aryl-EtherStretching: Imide

Asym C=OStretching:Imide

C-N Bending

1258.01

Aryl-EtherStretchingPEAA

1664.2C=O (COOH) Amide l

PEI

1728.1Sym C=OStretching :Imide

Fluoro-poly(ether imide) [6FDA + p-SED]

Fluoro-poly(ether amic acid) [6FDA + p-SED]

PEAA

744.31

CC

C

C

CF3

O O

O

HNC

O

CF3

S OO

O

O

OH

HN

HO

S

O

O

OC

C

C

C

CF3

O O

O

N

CF3

C

O

N On

6F-PEIn

6F-PEAA

Wavenumber (cm-1)1500 50010002000

1545.72




%T

725.31C-N Bending1061.07

1250.33


1784.4

725.29




C-N Bending

1258.01



PEI




PEAA

744.31

Wavenumber (cm-1)1500 50010002000

1545.72




%T

725.31C-N Bending1061.07

1250.33


1784.4

725.29




C-N Bending

1258.01



PEI




PEAA

744.31

254

The result indicates that the polymers have reasonable viscosity and molecular

weights. However, the molecular weights obtained by GPC, relative to polystyrene

standards were lower for pre-formulations. This observation was similar to the one

disclosed by a U.S. patent [44]. It attributed such lowering of molecular weights to a

dilution effect. In our experiments further dilution of the 6F-PEAA solution also took

place from 25 to 20% solid level during the preparation of [(6F-PEAA)/MMT clay]

nanocomposite pre-formulations.

4.5.1.3. Solubilities of [6FDA + p-SED] (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite films

The solubilities of (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite,

ULTEM1000, and KaptonH, , films were tested in acetone, THF, DMAc, DMF,

DMSO, BLO, NMP, methylene chloride and 0.1N H2SO4 over 24 hr at room

temperature. The solubility data of polymers and films are listed in Table 3.

Table-3 : Solubilities of [6FDA + p-SED] fluoro-poly(ether imide) (6F-PEI) and [(6F- PEI)/MMT clay] nanocomposites, ULTEM1000 and KaptonH films

Solubility of PEI and PEI/Clay Nano-composites films

Solvent

Acid

Sample

Acetone THF DMF DMSO DMAc BLO NMP CH2Cl2 H2SO4 **

Solid PEI ± + + + + + + + + Film of PEI/MMT clay

Nanocomposite Composition with %

Clay Contents

0 ± ± ± 1 ± ± ±

2.5 ± ± ± 5 ± ± ± 10 ± ± ± 15 ± ± ±

ULTEM1000 ± ± + ± + + Kapton H * ±

Solubility tested for approx. 1.0 sq. cm size films at RT (25°C) over 24 Hours *: As received Kapton H film; **: 0.1N solution in DI water; NA: Not available; + : Soluble at RT (25°C); ±: partially swollen film; : Film insoluble at RT.

The (6F-PEI) solid was soluble in almost all the solvents tested at room temperature.

Films of nanocomposite containing 0-15% diamine treated MMT clay, and

255

ULTEM1000 KaptonH were either insoluble or partially swelled over overnight at

room temperature in the above solvents. All these polymers were also unaffected by

0.1N H2SO4 except KaptonH, which was shown to be slight swollen.

4.5.1.4. Morphology

The X-ray diffraction patterns of Kunipia-F (MMT clay) and p-SED modified MMT clay

are shown in Figure 8. For MMT clay, a distinct peak at 2θ = 7.08. with d-spacing

calculated from the Bragg Equation was of 1.24 nm. Due to effective cation exchange

reaction about 1 nm gap formed within the MMT clay lamellae, and the diffraction peak

for p-SED modified MMT clay shifted to a lower angle, and appeared at 2θ = 6.215

having d-spacing of 2.26nm in the XRD spectral window range from 2θ = 4° to 10°.

Figure-8 : X-ray diffraction patterns of Kunipia-F MMT clay and p-SED modified MMT clay (i.e., Organosoluble clay) and [(6F-PEI)/MMT clay] nanocomposite films However, the X-ray diffraction patterns of the (6F-PEI) and [(6F-PEI)/MMT clay]

nanocomposite are shown to have no significant or obviously corresponding peaks for

either of MMT clay and p-SED modified MMT clay. The result indirectly shows that the

layered structure of the p-SED modified MMT clay has been disrupted. A more direct

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0

pSED Modifed MMT 7.08

6.215

0%1%

2.5%5% 10%

15%

Na-MMT ( KUNUPIA -F) Clay

Inte

nsity

(AU

)

2θ (degree)

(d = 2.26 NM)

(d = 1.24 NM)2θ =

2θ =

256

evidence of the dispersion of the layers can be provided by scanning electron microscopy

(SEM). The disorder and loss of structural regularity indicates exfoliation of MMT clay

lamellae in the [(6F-PEI)/MMT clay] nanocomposite at molecular level.

4.5.1.5. Color and transparency of polymer and nanocomposites films

Except for the film of (6F-PEI) which was almost colorless, the [(6F-PEI)/MMT clay]

nanocomposite films were dark brown to black in color as the clay content increased.

The ULTEM1000 and KaptonH films were yellow and amber in color respectively.

4.5.1.6. Glass transition temperature (Tg).

The glass transition (Tg) values, thermal decomposition of the (6F-PEI) and [(6F-

PEI)/MMT clay] nanocomposites film samples are reported in Table 4 and Figure 9(a).

The Tg of film samples were plotted against % clay content as shown in Figure 9(b).

The change in Tg values reflects a large variation in molecular structures. Tg of

nanocomposites films slightly increased with increase in % clay content due to the strong

interactions between the clay and 6F-PEI, in which the nanometer size clay galleries

limits the segmental motion of PEI. In other words, the distortion of the linearity of the

polyimide chain thereby reduced molecular chain rotation and thus providing less

interchain slippage, and increased chain stiffness [11, 19, 45-53].

These samples were also analyzed in XRD spectral window range from 2θ = 10° to 2θ

= 30°. The result was consistent with that of the solubility behaviour of polymer film and

also with the glass transition temperature (DSC) result. This could be explained in terms

of the presence of ‘spacer’ link such as sulfonyl group. This 'spacer' link reduces the

rigidity of the polymer chain which inhibits its packing. The increased inhibition of the

conformational rotation is also reflected in an increase in Tg values of the

nanocomposites [45-49]. In the case of [6FDA + p-SED] fluoro-poly(ether imide) (6F-

PEI), which is made from para and isomer of ether-containing diamine monomer with

257

sulfonyl (-SO2-) spacer group, the d-spacing and Tg values were 4.72Å and 293°C

respectively, whereas for ULTEM®1000, the d spacing and Tg were 5.24Å and 218°C

respectively. Both of these polymers were completely amorphous.

(a)

(b)

Figure-9 : (a) Tg of (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite films sample. (b) Plot of Tg against % clay content in nanocomposites

290

291

292

293

294

295

296

297

298

0 1 2.5 5 10 15

% Clay Content

Tg

(deg

C)

200 225 250 275 300 325

Hea

t Flo

w E

ndot

herm

ic (m

W)

Temperature (oC)

15% clay 10% clay 5% clay 2.5% clay 1% clay 0% clay

258

Table-4: Tg and thermal properties of (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposites, ULTEM000 and KaptonH films

TGA Thermal Stability

Air

Nitrogen

Film Sample

DSC

Tg [°C]

5% wt Loss

[°C]

Char yield @ 790°C

[%]

5% wt Loss

[°C]

Char Yield @ 790°C

[%]

[PEI/MMT clay] Nanocomposite

[% Clay]

0 293.0 544.0 0.00 561.0 52 1 293.3 526.7 0.02 527.8 56

2.5 294.6 518.2 0.96 540.4 57 5 295.5 523.5 1.12 546.0 57

10 297.0 519.2 3.39 529.8 57 15 297.1 514.9 5.93 534.0 56

ULTEM1000 218.0 522.0 0.00 526.0 48 KaptonH * 407.0a 601.0 0.00 603.0 53

*: As received Film a: Measured by Thermomechanical analysis (TMA)

4.5.1.7. Thermal properties

4.5.1.7.1. Thermal stability

Evaluating the thermal stability of polymers is important for determining the thermal

performance of polymer at a given upper use temperature limits. Isothermal

thermogravimetric (I-TGA) analysis and/or dynamic thermogravimetric (TGA) analysis,

thermo-oxidative stability (TOS), and long-term isothermal-ageing weight-loss

measurement techniques are usually used. Of these techniques, dynamic TGA is widely

used because it requires only a small quantity of sample and the entire study is over in a

few hours. However, for this research, we have determined thermal stability by two

techniques and also confirmed the results with that obtained from a kinetic method of

characterising the thermal degradation of polymeric materials. A 5% weight loss for

nanocomposites films in nitrogen was observed at a temperature on an average about

15oC higher than in air (Figure 10). The % char yield (residue) in nitrogen was about

259

4% higher than (6F-PEI) and in the range of 56% at 790oC (Figure 11 and Table 4).

Figure-10 : TGA of (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite films in flowing air and nitrogen Figure 11: Plot of % char residue yield of (6F-PEI) and [(6F-PEI)/MMT clay] nano-composite films in air and nitrogen against % clay content

50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 8000

20

40

60

80

100

AIR

NIROGEN%

WE

IGH

T L

OSS

TEMPERATURE (oC)

0% clay (Air) 1% clay (Air) 2.5% clay (Air) 5% clay (Air) 10% clay (Air) 15% clay (Air) 0% clay (Nitrogen) 1% clay (Nitrogen) 2.5% clay (Nitrogen) 5% clay (Nitrogen) 10% clay (Nitrogen) 15% clay (Nitrogen)

0

10

20

30

40

50

60

0 1 2.5 5 10 15

% Caly Content

% C

har

Yie

ld

% Char Yield in Nitrogen

% Char yie ld in Air

260

4.5.1.7.2. Kinetics study of thermal degradation.

At least five kinetic methods are available in the literature to characterize the thermal

degradation of polymeric materials [54]. Of these, Coats and Redfern method [17] is

very straight forward and easy to use, as it uses data of thermal decomposition at give

temperature obtained directly from the D-TGA. The Coats and Redfern equation given

below was used here to evaluate the thermal stability of polyimide and various

nanocomposite films.

−

−

=

−−

RTE

ERTAR

Ta

a

21ln)1(lnln 2 φα (2)

where α is fraction decomposed at temperature T

φ is heating rate

Ea is activation energy

R is Universal gas constant

A is Arrhenius frequency factor

Rao et al. [55] used the above equation for the determination of activation energy for

the thermal degradation of polyimides derived from ether ketone diamines.

Plots of ln [-ln (1-α) / T2] vs 1 / T of [6F + p-SED] (6F-PEI) and [(6F-PEI)/MMT clay]

nanocomposite films tested in air are given in Figure 12(a). Activation energy (Ea) was

calculated by multiplying universal gas constant with the slope of plot of ln [-ln (1-α) /

T2] vs 1 / T. Plots of activation energy vs percent clay content in [(6F-PEI)/MMT clay]

nanocomposite films tested in air and nitrogen are given in Figure 12(b). The activation

energy was found to increase with increasing clay content in [6F-PEI/MMT clay]

nanocomposite respectively. It is also observed both the environment cases, the

activation energy increased with increasing in clay content. However, such rate increase

was smaller for nitrogen environment than for air, indicating that high thermal stability

261

for the nanocomposites in the air environment obviously has been achieved. The

activation energies for KaptonH, ULTEM1000 films were not calculated.

(a) (b) Figure 12(a): Plot of ln [-ln (1-α) / T2 vs 1 / T of (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite films; (b): Plot of activation energy vs % clay content in nanocomposite films

(Kinetic study of thermal degrdation by TGA in air)

y = -16041x + 4.0384R2 = 0.9999

y = -21339x + 10.203R2 = 0.9954

y = -23271x + 12.683R2 = 0.999

-18

-17.5

-17

-16.5

-16

-15.5

-15

-14.5

-14

-13.5

-130.0011 0.00112 0.00114 0.00116 0.00118 0.0012 0.00122 0.00124 0.00126 0.00128 0.0013

0% clay5% clay15% clayLinear (0% clay)Linear (5% clay)Linear (15% clay)

ln [-

ln (1

-α) /

T2

]1/T

(Kinetic study of thermal degrdation by TGA in air)

y = -16041x + 4.0384R2 = 0.9999

y = -21339x + 10.203R2 = 0.9954

y = -23271x + 12.683R2 = 0.999

-18

-17.5

-17

-16.5

-16

-15.5

-15

-14.5

-14

-13.5

-130.0011 0.00112 0.00114 0.00116 0.00118 0.0012 0.00122 0.00124 0.00126 0.00128 0.0013

0% clay5% clay15% clayLinear (0% clay)Linear (5% clay)Linear (15% clay)

ln [-

ln (1

-α) /

T2

]1/T

y = -0.1466x2 + 4.409x + 148.78R2 = 0.9336

y = -0.3622x2 + 9.2651x + 133.55R2 = 0.9582

0

50

100

150

200

250

0 2 4 6 8 10 12 14 16

% Clay Content in Nanocomposite Film

Act

ivat

ion

eneg

ry( k

J/m

ole)

Air EnvironmentNitrogen EnvironmentPoly. (Nitrogen Environment)Poly. (Air Environment)

262

4.5.1.7.3. Thermo-oxidative stability (TOS) study

Isothermal thermo-oxidative stability (TOS) measurements of [6F + p-SED] Fluoro-

poly(ether imide) (6F-PEI), and series of [(6F-PEI)/MMT clay] nanocomposites,

ULTEM1000 and KaptonH films were carried out in a programmable oven at 300 oC

for 300 hours in air environment.

Film samples were preheated at 150oC for one hour and further heated to 300oC and

their weights at this point taken as the reference or 100% weight value. During the test,

the crucibles with the samples were removed from the oven simultaneously at

appropriate times, and immediately sealed for cooling. They were weighed and then

returned to the oven immediately for further aging. Neglecting the initial weight loss of

all the samples tested, which is thought to be associated with solvent and absorbed

moisture removal, an approximate weight loss of only 3.0% occurred for and

ULTEM100, whereas 4.4% weight loss for KaptonH, weight loss for [6F-

PEI/MMTclay] nanocomposites films were in the range of 2.9-1.2% over 300 hours

(Figure 13).

Figure-13 : Thermo-oxidative stability of (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite films at 300oC for 300 hours in air environment

80

85

90

95

100

0 24 48 72 96 120 144 168 192 216 240 264 288 300

Hours

% W

t. R

etai

n

0 % Clay

1 % Clay

2.5 % Clay

5 % Clay

10 % Clay

15 % Clay

263

The % weight retention increased by 58% as the clay content increased from 0 to 15%

in the nanocomposite film, indicating significant improvement in the thermal stability.

The isothermal weight loss study also confirmed the thermo-stability explained by the

results obtained by kinetic study using the Coats and Redfern method (Table 5).

Table-5: Thermo-oxidative stability and activation energy of thermal degradation of (6F-PEI), [(6F-PEI)/MMT clay] nanocomposite, ULTEM1000 and KaptonH films

Activation Energy for Thermal Degradation Ea

[kJ/mole]

Film sample

TOS

Weight retained

@ 300°C for

300 Hr

[%]

Air

Nitrogen

PEI/ MMT clay Nanocomposite [% Clay]

0 97.1 133.4 144.6 1 97.2 137.9 156.2

2.5 97.4 157.3 159.5 5 97.8 177.4 170.6

10 98.9 182.9 173.53 15 98.0 193.5 183.6

ULTEM1000 97.0 N/A N/A KaptonH * 95.6 N/A N/A

*: As received Film a: Measured by Thermo mechanical analysis (TMA)

4.5.1.8. Thermomechanical properties

The thermo-mechanical properties, such as storage modulus E', tan δ max, and loss

modulus E" values of [6FDA + p-SED] fluoro-polyetherimide films are also tabulated in

Table 6. The peak of tan δMax was identified as the glass transition temperature, because

a large decrease of the storage modulus E' occurred at that temperature (Figure 14).

On comparing the Tg of fluoro-polyetherimide and nanocomposite films (293 to

297°C) as measured by DSC with those of tan δ value of 293°C to 295°C measured by

DMA, in Figure 14, it was noted that the Tg values obtained from DMA were slightly

higher. The thermo-mechanical properties of polyimides are directly related to the inter-

and intra-molecular chain conformation rotation flexibility beside the chemical structure

[4, 56]. They also depend on the previous heat history of the polymer samples.

264

Table-6: Thermo-mechanical properties of (6F-PEI), [(6F-PEI)/MMT clay] nanocomposite, ULTEM1000 and KaptonH films

TMA DMA

Storage Modulus [MPa]

Film Sample

CTE

[mm/°C] 100°C 200°C

Tan δ (Max) [°C]

Loss Modulus E’’(Max)

[°C] [6F-PEI/MMT clay]

Nanocomposite [% Clay]

0 6.06 X 10-5 187.4 139.1 294.1 293.3 1 5.89 X 10-5 223.5 177.0 296.6 287.7

2.5 5.52 X 10-5 233.1 185.8 298.4 289.2 5 5.31 X 10-5 194.9 153.7 301.9 292.4

10 4.87 X 10-5 261.9 209.0 304.6 295.3 15 4.67 X 10-5 314.6 258.0 302.9 294.8

ULTEM1000 5.95 X 10-5 179.3 116.5 225.8 223.3 KaptonH * 3.15 X 10-5 269.7 214.8 403.0 419.0

*: As received Film; a: Measured by Thermo mechanical analysis (TMA) The results could be compared with increasing order of rigidity and stiffness in the

polymer backbone provided by exfoliation of p-SED diamine modified MMT clay as

indicated by the increasing value of glass transition temperature. For all the samples

tested, one dynamic loss peak corresponding to β relaxation was always observed near

100°C. This β relaxation is considered to be due to inter-plane slippage of aromatic and

imide rings. [57].

Figure-14 : Plot of Loss modulus against temperature for (6F-PEI), [(6F-PEI)/MMT clay] nanocomposite films

50 100 150 200 250 300 350

10

100

1000

E"

α-Realxation

β-Relaxation

Los

s Mod

ulus

E''

(MPa

)

Temperature (oC)

0% clay 1% clay 2.5% clay 5% clay 10% clay 15% clay

265

4.5.1.9. Coefficient of thermal expansion (CTE)

The coefficient of thermal expansion (CTE) value of 6F-PEI film was (6.06x10-5

m/m°C), which was higher than KaptonH (3.15x10-5m/m°C), but consistent with that of

flexible poly(ether imide) ULTEM1000 (5.95x10-5m/m°C). The polyimide film

prepared from its solution generally has a higher CTE value than that from the

corresponding poly(amic acid) due to its high temperature curing (imidization)/heating

history [38, 58]. On the other hand, poly(ether imide)s containing flexible 'spacer' links,

such as -O-, -C(CH3)2-, -C(CF3)2-, -SO2-, etc. and meta substituted aromatic ring would

tend to have higher CTE values [16]. However, for the [6F-PEI/MMT clay]

nanocomposite films, the introduction of a small amount of clay effectively distorted the

linearity of the polyimide chain thereby reducing molecular chain rotation and CTE. In

addition, the CTE values continuously decreased to about 22% as the clay content

increased from 0 to 15% as shown in Figure 15. This behavior was similar to the rigid

rod type polyimides, which have very low CTE value similar to metals.

Figure-15 : Plot of CTE values against % clay content in (6F-PEI), and [(6F-PEI)/MMT clay] nanocomposite films

40

45

50

55

60

65

0 1 2.5 5 10 15

% Clay Content

CT

E (m

icro

n/m

deg

C)

266

4.5. 1.10. Hydrolytic stability

Moisture absorption and diffusion properties are important with regards to their

practical use in microelectronics and aerospace composites. The absorbed water in

polymer structures affects their performance and long-term stability [59-60]. Very

significant lower moisture absorption values were noted for [6FDA + p-SED] fluoro-

poly(ether imide) (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite films at 100 RH at

50°C. The values were in the range of 0.55% to 0.71% for the fluoro-poly(ether imide)

(6F-PEI) and nanocomposites films containing hydrophobic hexafluoroisopropylidene -

C(CF3)2- groups. However, there was a slight increase in moisture absorption as the %

clay content increased in the composites (Table 7). This may be possibly due to the high

temperature thermal treatment during the imidization steps which may have decomposed

some of the organic cations resulting in localized agglomeration of clay particles on the

surface of nanocomposite films as the % weight loading of MMT clay increased beyond

5%. However, it was noted that these values were still lower than those of non-

fluorinated poly(ether imide)s (PEI) and polyimide (PI), reported in product brochure

such as ULTEM1000 (1.52%) and KaptonH (3.0%) films, which were used as

'controls' in this study. [61-65].

Table-7: Moisture absorption of (6F-PEI), [(6F-PEI)/MMT clay] nanocomposites, ULTEM1000 and KaptonH films

Polymer film

Moisture absorption at 50°C for 100 Hr at 100 RH

[%] [(6F-PEI)/MMT Clay] Nanocomposite film,

[% Clay content]

0 0.55 1 0.56

2.5 0.58 5 0.61

10 0.66 15 0. 71

ULTEM1000 1.52

KaptonH * 3.00 *: As received Film

267

4.5.1.11. Mechanical properties

The mechanical properties of [6FDA + p-SED] fluoro-poly(ether imide) (6F-PEI) and

[(6F-PEI)/MMT clay] nanocomposite, and [PMDA + ODA] nanocomposite films are

summarized in Table 8. For the fluoro-poly(ether imide) [6FDA + p-SED] and [(6F-

PEI)/MMT clay] nanocomposite films, the Young’s modulus of elasticity was in the

range of 17 to 21 GPa, ultimate stress in the range of 11 to 59 MPa, and elongation at

break of 0.9 to 13%.

Table-8: Mechanical properties of 6F-PEI and nanocomposite films compared with [PMDA + ODA] polyimide film

PEI/MM

clay Nanocomposite [% Clay]

Modulus

E (GPa)

Ultimate Stress

σ (MPa)

Elongation @ Break

(%)

[6FDA + p-SED] 0 14.10 62.02 12.56 1 20.15 59.13 4.38

2.5 21.03 54.96 3.16 5 20.22 29.09 1.58

10 18.49 19.35 1.25 15 17.64 11.68 0.92

[PMDA/ODA]*

0 2.7 90 30 1 3.9 87 8 2 5.7 69 2 3 5.2 40 0.9

*: [19] The result was compared with the increase in modulus and decrease in % elongation at

break values, which were 5.2 GPa and 0.9% respectively for [PMDA + ODA] PI samples

at 3% clay content as reported by Agag and coworkers [19]. For all the nanocomposites

film samples tested, the modulus increased somewhat linearly up to 2.5% clay content in

the sample, and then decreased slightly as the clay content increased further. However, at

15% clay content, it remained higher (~31%) than the neat polymer (Figure 16). The

increase in modulus could be explained by the fact that the amount of clay galleries is

268

increased linearly to the % clay exfoliated [22]. However, a slight decrease in modulus

and a significant decrease of % elongation indicating the loss of some flexibility or

increase in brittleness may be due to thermal decomposition of organic cations resulting

in the aggregation of clay as the clay loading increased in the nanocomposite films in our

study.

Figure-16 : Modulus and % elongation as function of % clay content in [(6F-PEI)/MMT clay] nanocomposites films 4.5.1.12. Surface properties.

Adhesion of polyimides to various inorganic interfaces, such as silicon, silicon oxide,

aluminum, and copper must be well defined in the construction of IC devices. Good

adhesion is a must not only at low temperature, but also after exposure of up to several

minutes at higher temperatures in the range of 200-400°C [66]. Results of polyimide

adhesion studies on various substrates have shown that polyimides adhere well to

aluminum surface (i.e. aluminum oxide) and reasonably well to other metal surfaces

[67].

Mod

ulus

(Gpa

)

MMT Clay Content ( %)

Elo

ngat

ion

at B

reak

( %

)

0

5

10

15

20

25

0 2 4 6 8 10 12 14 160

5

10

15

20

25

30

35

[6FDA + p-SED] Modulus

[PMDA + ODA] Modulus

[6FDA + p-SED] Elongation

[PMDA + ODA] Elongation

Mod

ulus

(Gpa

)

MMT Clay Content ( %)

Elo

ngat

ion

at B

reak

( %

)

0

5

10

15

20

25

0 2 4 6 8 10 12 14 160

5

10

15

20

25

30

35

[6FDA + p-SED] Modulus

[PMDA + ODA] Modulus

[6FDA + p-SED] Elongation

[PMDA + ODA] Elongation

269

As mentioned earlier that for last several years there has been significant interest

generated for the novel uses of polymer/clay nanocomposites and their applications as

high temperature thin film protective materials. The polymer nanocomposites have also

been investigated for applications such as high barrier and shielding coatings for

microelectronics and telecommunication devices. Study of surface properties of such

coating materials therefore would provide some meaningful information of material’s

adhesion behaviors on and/or de-lamination from given substrates due to changes in their

surface energies. Surprisingly, up-to-date literature search did not reveal any reference

on the study of surface properties of [fluoro-polyimide (6F-PI)/MMT clay]

nanocomposite films. Thus experiments were carried out to study the effect of clay

concentration in nanocomposite films on the surface energy at room temperature in air

environment.

It must be emphasized that polymer adhesion is a complex phenomenon and the

effective adhesion is only partly determined by interfacial properties [68]. Similarly, the

surface energy (γS) of polymer solid can only be measured by indirect methods. Several

methods have been developed over a time. One of these methods consists of contact

angle (θ) measurement of various liquids on a given solid polymer surface [69-74]. As

the contact angle is a measure of the surface energy of the polymer, higher polymer

surface energy results in lower contact angle, or greater change in wettability. Contact

angle measurement is also an important method, which provides true surface information

to show the types of functional groups present at the surface and evaluate the chemical

structural effects on the surface properties of the polymer.

We have determined the surface energies of (6F-PEI) and [(6F-PEI)/MMT clay]

nanocomposite films by using One-Liquid method and Two-Liquid method.

270

4.5.1.12.1. One-Liquid method

An equation, well known as Good-Girifalco equation [75-76] is expressed as

γS = [γLV (1 + Cos θ)]2 / 4φ2 (6)

where, θ is the contact angle

γ is surface energy

the subscripts S, L and V refer to solid, liquid and vapor respectively

φ is a constant between solid and liquid interface.

By knowing the value for φ for testing liquid and solid polymer pair, one can calculate

the surface energy (γS) from the contact angle data using equation (6). However, in the

zeroth order approximation, Good and Girifalco suggested that value of φ was equal to

unity [75-76].

4.5.1.12.2. Two-Liquid Geometric method

Owens and Wendt and Kaelble [77-78] generalized the Fowkes’ equation [79-80]

γSL = γS + γLV – 2 ( γdS

. γdLV ) 1/2 - 2 ( γp

S . γpLV ) 1/2 (7)

By combining it with modified Young equation

γLV Cos θ = γSL - γLV (8)

thus obtained a useful and workable equation

γLV (1+ Cos θ) + 2 (γ dS. γ dLV )

1/2 + 2 (γ pS . γ pLV )

1/2 (9)

where γLV is surface tension of liquid in equilibrium with its own vapor

γSL is interfacial tension between liquid and solid surface

γSV is surfaced tension of solid in equilibrium with the saturated liquid vapor

θ is the contact angle.

271

The superscript d refers to a dispersion component and p refers to a non-dispersion

component, including all typical interactions established between the liquid and polymer

surface, such as dipole-dipole, dipole-induced dipole and hydrogen bonding, etc. [69]

Equation (9) was used in the calculation of surface energy (γS) of nanocomposite films

as by Owens and co-worker’s Two-Liquid Geometric method. In this method, two

liquids (in our study, deionised water and formamide) with known surface tension

component values (γdL) and (γp

L), are used for contact angle (θ) measurement. Then one

could easily calculate the surface tension component values (γdS

) and (γpS) for polymer

solid surface by solving simultaneously the following two equations

γLV1 (1+ Cos θ1) + 2 (γ dS . γ d LV1 )

1/2 + 2 (γ pS . γ p LV1) 1/2 (10)

γLV2 (1+ Cos θ2) + 2 (γ dS . γ d LV2 )

1/2 + 2 (γ pS . γ p LV2) 1/2 (11)

where θ1 and θ2 are the contact angle for DI-water and formamide respectively.

Since it is known that when a liquid drop is in contact with a smooth, planer

homogeneous solid surface, it exhibits an equilibrium contact angle as shown in Figure

17.

Figure-17 : An immobile droplet of liquid on a solid polymer film surface showing a three phase force line. Therefore, the surface energies of neat (6F-PEI) films and [(6F-PEI)/MMT clay]

nanocomposite films were calculated from contact angles using equation (12)

Solid polymer film surface

γSL

γSV

γLV

Liquid

Saturated vapor

θ

272

γS = γdS + γp

S (12)

where surface energy γS is the sum of surface tension component contributed from

dispersion and non-dispersion parts, and the value of (γdL) and (γp

L) of reference liquids,

water and formamide provided by Kaelble [81 and Good [82], and given in Table 9.

Table-9: Surface Tension parameter in (mJ/m2) of testing liquids [81-82]

Parameter Water Formamide γ (or γLV) 72.8 58.0 γp

(or γpLV) 51.0 18.7

γd (or γd

LV) 21.8 39.5

The contact angles data and their standard deviation for six films for DI-water and

formamide are listed in Table 10.

Table-10: Contact angle determination (in Degree) on the surface of 6F-PEI and nanocomposite films

Testing liquid Contact angle of film sample [(6F-PEI)/modified MMT clay]

nanocomposite [% MMT clay]

Water Formamide

0% clay Contact angle θ

(Standard deviation)

83.60

(2.05)

75.7

(1.50) 1% Clay

Contact angle θ (Standard deviation)

79.78

(2.43)

72.37

(1.70) 2.5% clay


78.06

(1.93)

70.95

(1.50) 5% clay


74.00

(1.0)

68.05

(0.7) 10% clay


73.36

(1.40)

67.27

(1.45) 15% clay


65.80

(1.87)

60.43

(1.43) The surface energy γS of the sample calculated by both methods is tabulated in Table

11. The high surface tension liquid DI-water gave larger contact angles for these film

samples as compared to formamide. The contact angle is also influenced by the chemical

273

properties of testing liquids [83], and the surface topography of nanocomposite film.

Table-11: Surface energy of (6F-PEI) and [(6F-PEI)/MMT clay] nanocomposite films using One-Liquid method and Two-Liquid methods

Surface energy (γS) [mJ/m2]

One-Liquid method Two-Liquid Method

Film sample of

[(6F-PEI)/modified MMT clay] nanocomposite [% MMT clay] Water Formamide Water-Formamide

0.0% 22.90 22.57 23.62 1.0% 25.23 23.99 25.67 2.5% 26.51 25.50 27.08 5.0% 29.62 27.37 29.89

10.0% 30.12 27.98 30.64 15.0% 31.11 30.85 32.16

The surface energy γS calculated by One-Liquid method varied from 22.9mJ/m2 for

neat 6F-PEI film to 31.1mJ/m2 for [(6F-PEI)/MMT clay] nanocomposite film with 15%

clay for water. Whereas, γS varied from 22.6mJ/m2 for neat 6F-PEI film to 30.9mJ/m2 for

[6F-PEI/MMT clay] nanocomposite with 15% clay for formamide. This indicates that

the polarity of testing liquid also played an important role to the surface energy

calculation.

The increase in surface energy as calculated for both liquids was in the range of 8.21-

8.54mJ/m2. The trends of increasing surface energy values were comparable to the values

determined by Two-Liquid method; however, the latter was slightly higher. It was also

noted that the contact angle of [(6F-PEI)/MMT clay] nanocomposite film decreased in

the presence of hydrophobic clay. The extent of increase in the surface energy depended

on the % concentration of clay present in the nanocomposites, as graphically represented

in Figure 18. One interesting observation made here was that the rate of increase in

surface energy increase was higher for the nanocomposite having clay content from 0 to

5% than that from 5 to 15%. The higher rate of increase in the surface energy could also

be possibly attributed to the uniform distribution of hydrophobic MMT clay in the

nanocomposite film at lower clay concentration, as well as the quality and nature of

274

microstructure of exfoliated clay galleries present on the surface of the films. Whereas,

the subsequent lower rate of surface energy increase could be due to localized

aggregation of clay galleries on the film surface as the clay content increased further. It

would be of further scientific interest to carry out study on the effect of exfoliated clay in

the polymer system and determine the mechanism of such decline in contact angle.

20

22

24

26

28

30

32

34

0 2 4 6 8 10 12 14 16

% MMT Clay Content

Surf

ace

Ene

rgy

( mJ/

m.m

)

Water

Formamide

Water-Formamide

Figure 18: Surface energy as function of % clay content in [(6F-PEI)/MMT clay] nanocomposite films 4.6. CONCLUSION A high temperature stable [6FDA + p-SED] fluoro-poly(ether imide) (6F-PEI) has

been synthesized by solution polymerization. A series of [fluoro-poly(ether imide) (6F-

PEI)/MMT clay] nanocomposites films were prepared. The FT-IR study confirmed that

poly(ether amic acid) (6F-PEAA) was successfully converted to poly(ether imide) (6F-

PEI) by thermal imidization method. The solid [6FDA + p-SED] poly(ether imide) (6F-

PEI) was soluble in almost all the organic solvents tested in this study at room

temperature. However, the [(6F-PEI)/MMT clay] nanocomposite films showed excellent

solvent resistance at room temperature.

275

The nanocomposites had very good thermal stability in air and nitrogen environment

as shown by TGA study. Their glass transition temperature (Tg) values increased with

increasing clay components. In addition, these trifluoromethyl (-CF3) groups-containing

poly(ether-imide)/clay nanocomposites showed a sharp lowering of coefficient of

thermal expansion (CTE) in the range of 10–22%, The % weight retention of neat fluoro-

poly(ether imide) (6F-PEI) at 300oC for 300 hours in air was 97%, whereas, the [(6F-

PEI)/MMT clay] nanocomposite films retained weights in the range of 98%. This was

supported by the increase in their activation energy of thermal degradation in the kinetic

study.

The [6FDA + p-SED] Fluoro-poly(ether imide) (6F-PEI) exhibited reduced water

absorption (< 0.6%) relative to non-fluorinated polyimides (non nanocomposite) film

such as ULTEM1000 and KaptonH [16]. Very significant lower moisture absorption

(in the range of 0.55% to 0.71%) was noted for [(6F-PEI)/MMT clay] nanocomposite

films at 100 RH at 50°C, which are significantly lower than literature reported value of

the control sample of ULTEM1000 (1.52%) [62] and KaptonH (3.0%) films [64].

The fluoro-poly(ether imide) [6FDA + p-SED] is an amorphous polymer as

determined by XRD measurements (d spacing = 4.72Å). The spectra of [(6F-PEI)/MMT

clay] nanocomposite in the scanning range of XRD spectral window range from 2θ = 4°

to 2θ = 10° showed no obvious crystalline peaks corresponding to the neat MMT clay or

p-SED modified (ion exchanged) clay (Organosoluble clay), indicating mixing and

reaction of amino functional on modified clay with PEAA and its maximum exfoliation

in nanocomposite.

Modulus of elasticity increased by about 38%, whereas the ultimate stress and %

elongation at break values decreased significantly. Higher clay content resulted in

276

lowering of contact angle on average of 20.7%, which in turn, resulted in increased

surface energy, which would thus possibly provide a good way to control its wettability

and adhesion.

These fluoro-poly(ether imide)/MMT clay nanocomposites would be ideal candidates

for thin film coating applications such as high temperature insulators and dielectrics for

micro-electronic packaging, as well as substrates for electronic flex circuit and matrix for

high performance composites for aerospace, advanced aircraft and under the hood

automobile engine components, and materials for gas separation and fuel cell barrier

membranes [84-85].

The knowledge on the properties of (6F-PEI)s, (6F-CoPEI)s and nanocomposites

materials based on these polymers and oranosoluble clays, is very valuable. There exists

a scope for their further development and R&D of newer polyimide/inorganic

nanocomposites ‘Ceramers’ based on these fluoro-poly(ether imide)s and exploitation of

state-of-the-art reinforcing materials, such as, single walled carbon nanotubes (CSWNT),

boron nanotubes (BNT) for the commercial development of their newer industrial

applications

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79. F. W. Fowkes, in “Adhesion and Adsorption of Polymers”, Polymer Science and

Technology, Vol12A, L. H. Lee, (Ed.), Plenum Press, New York 1980, p. 43.

80. F. W. Fowkes, in “Contact Angle, Wettability and Adhesion”, Advances in

Chemical Series 43, R.F. Gould, (Ed.), American Chemical Society, Washington,

DC, 1964, p. 99.

81. D. H. Kaelble, “Physical Chemistry of Adhesion”, Wiley Interscience, New York,

1970, p. 149.

282

82. R. J. Good, in “Contact Angle, Wetting and Adhesion”, K. L. Mittal, (Ed.), VSP,

The Netherlands, 1993, p. 3.

83. R. P. Schneider, J. Adhesion Sci. Technol., 11 (1997) 65.

84. R. H. Vora P. K. Pallathadka, S. H. Goh, in “Polyimides and High Performance

Functional Polymers”, M. J. M. Abadie, B. Sillion (Eds.), STEPI-6, University of

Montpellier, Montpellier, 2003, p 191.

85. R. H. Vora, P. K. Pallathadka, S. H. Goh, T. S. Chung, Y. X. Lim, T. K. Bang,

Macromol. Mater. Eng. 288 (2003) 337.

283

CHAPTER - 5

GENERAL CONCLUSION

AND

RECOMMANDATION

284

5. CONCLUSION AND RECOMMANDATION

5.1. Conclusion

A brief history of the commercial development of conventional polyimide (PI) and

fluoro-polyimide (6F-PI) based products was highlighted and discussed in the

Introduction chapter (Chapter 1). Also the scope of my PhD research and objectives were

outlined and given in the Chapter 1.

One of the objectives of my PhD research was to synthesize and develop fluorinated

polymers such as fluoro-poly(ether imide) (6F-PEI) and fluoro-copoly(ether imide) (6F-

CoPEI) materials having desired or better thermal properties [viz. higher glass transition

temperature (Tg), higher thermo-oxidative stability (TOS), etc.], and very good electrical

insulation [viz. lower dielectric constant] performance for the electronic and aerospace

application than the commercially available polyimides, as listed in Table 27 of the

section 1.3 of Chapter 1. These polyimides were (1) EYMYD, a fluorinated poly(amic-

acid) (6F-PEAA) solution product based on 6FDA and BDAF, which was previously

available for a short time until 1995 from Ethyl Corp. Baton rouge LA; (2) conventional

polyimide KaptonH, based on PMDA and ODA, currently available from E. I. Dupont

& Co. Wilmington, DE; and (3) non-fluorinated poly(ether imide) PEI, ULTEM1000

based on BPADA and m-PDA, also currently available from General Electric Corp.

Schenectady, N.Y, USA. The target properties requirement was set for the new (6F-PEI)

and (6F-CoPEI) and also listed in Table 27 in Section 1.3 of Chapter 1.

After careful designing and considering their chemical compositions, several new

fluoro-poly(ether imide) (6F-PEI) and fluoro-copoly(ether imide) (6F-CoPEI)

compositions were successfully synthesized from the commercially available monomers,

based on the polymer composition approach scheme given in Figure 30 in Section 1.3 of

Chapter 1.

285

The neat 6F-PEI and 6F-CoPEI polymers as well as of their fabricated films, were

systematically characterized, and their properties were compared with the commercially

available fluorinated and non-fluorinated polyimides. This research work helped to

develop a clear understanding of the structure-properties relationship in terms of

chemical and physical properties, as well as the thermal degradation kinetic of 6F-PEI

and 6F-CoPEI films [Chapters 2 and 3].

The target polymer, [6FDA + p-SED] fluoro-poly(ether imide) was found to be an

ideal replacement of the current commercially available polyimides. This amorphous

polyimide has a reasonably high Tg, (293°C), excellent long term (300 hours) thermo-

oxidative stability (TOS) at 300°C in air atmosphere (>96 % weight retention) indicating

potential continuous use temperature in the range of 200-225°C. It has lower moisture

uptake (0.55% at 50°C and 100% relative humidity (RH) for 100 hours) and low

dielectric constant (<2.8 at 10MHz.), as well as comparable and acceptable mechanical

and CTE properties. The generalized target properties achieved for both fluoro-

poly(ether imide) (6F-PEI) and fluoro-copoly(ether imide) (6F-CoPEI) polymer films are

listed in Table 1.

Table-1 : Target properties achieved for fluoro-polyetherimide (6F-PEI) and fluoro- copoly(ether imide) (6F-CoPEI) polymer films.

PROPERTIES EYMYD

(Ethyl) PEAA

ULTEM1000 (GE ) PEI

KaptonH (Dupont)

PI

6F-PEI Target

properties (R. Vora)

6F-PEI and

6F-CoPEI Properties achieved (R. Vora)

Tg (°C). 267 220 407 250-270 250-300 TOS @ 315°C./ 300 Hrs. (% wt loss) < 8 % < 5% < 10 % < 5 % < 4 % Continuous Use Temp. (°C) 190 170 240 > 200 200-225 Dielectric Constant @ 10 MHz. 2.99 3.15 3.5 < 2.90 < 2.8 Moisture Uptake @ RT/24 Hrs. (%) 0.55 1.5 % 2.8 % < 0.70 % < 0.56 % Chemical Resistance to Acid & Base Yes Yes Yes Yes Yes Tensile Strength (psi) 13,300 15,200 33,500 > 12,000 > 12,000 Elongation @ Break (%) <10 % 60 72 > 10-100 > 10-100 Modulus (Kpsi) 353 430 430 > 400 > 400 CTE (ppm/°C) 62 59.5 31.5 < 62 < 61 Process: Not Possible (N) Melt (M) Solution Cast (S)

(S) (M) (N) (M), (S) (M), (S)

286

For the first time the molar polarization PLL and PV values of ‘Phthalimide’ and

‘Pyromellitimide’ groups typically present in polyimide structures have been derived and

established based on additive group contribution method defined by Lorentz and Lorenz,

and Vogel theories. It was also established that the dielectric constants of copolyimides

do not have the simple additivity of the dielectric constant values of their individual

homopolymeric components given in the chemical structural repeat unit, and hence the

estimation of dielectric constant of copolyimides became difficult. Because of that, two

additional mathematical model (equations) were derived based on the mathematical

expression defined by Lorentz and Lorenz, and Vogel theories for the estimation of

dielectric constant (electrical properties) of copolyimides and (6F-CoPEI) [Chapter 3].

These equations are known as Vora-Wang equations. The calculated (estimated)

dielectric constants for 6F-CoPEI, and commercial ULTEM1000, KaptonH, EYMID,

SIXEF-44, etc. other polyimides were in good agreement with their experimental and

literature values. Therefore, these equations can be employed to calculate (estimate)

dielectric constant values of any unknown or new copolyimides compositions well

before they are synthesized in laboratory, as long as the chemical structures of their

repeat units are known.

The nano-scale technology is also an ongoing focus of intense research at various

research institutes worldwide to develop polymer/inorganic nano-composites or hybrids.

Due to its reasonably good solubility in dipolar aprotic solvents, a precursor fluoro-

poly(ether amic acid) (6F-PEAA) of [6FDA + p-SED] fluoro-poly(ether imide) (6F-PEI)

having high Tg was selected as an ideal candidate to formulate nanocomposites with

inorganic materials, such as organo-soluble clay derived from MMT mineral clay. The

mineral clay is typically treated with an organic quaternary ammonium salt to get

organo-treated inorganic clay (i.e., organo-soluble clay, for example). Thus a series of

287

[6FDA + p-SED] fluoro-poly(ether amic acid) (6F-PEAA) was first prepared, and from

which [(6F-PEAA)]/Montmorillonite (MMT) clay nanocomposites formulations having

a varying percent of p-SED treated MMT clay (i.e., organo-soluble clay) were

successfully synthesized. The organo-soluble clay was achieved by modifying the

surface chemistry of MMT clay by an ion exchange technique using p-SED rather than

quaternary ammonium salt. It was then successfully incorporated into fluoro-poly(ether

amic acid) (6F-PEAA) polymer matrix, and [(6F-PEAA)/MMT clay] nanocomposites

pre-formulations were achieved. The films of [(6F-PEI)/MMT clay] nanocomposites

were fabricated from the pre-formulations by casting wet films and subsequent thermal

imidization treatment steps at elevated temperature. The films were characterized for

their solubility, thermal, mechanical and surface properties. The result indicates that

[(6F-PEI)/MMT clay] nanocomposites films with exfoliated clay galleries have

‘Ceramer’ type properties including desirable morphologies and properties, such as

improved toughening, higher thermals stability, lower coefficient of thermal expansion,

and modifiable surface properties [Chapter 4].

As we have seen in the Chapters 2, 3, and 4, the research objectives were

systematically achieved successfully through meticulous planning, designing polymer

compositions, executing experimentation, fabricating their films and properties

characterization. The result of this research indicates that these fluoro-poly(ether imide)s

(6F-PEI) and fluoro-copoly(ether imide)s (6F-CoPEI) would prove to be versatile

engineering plastics having many desired properties, which may allow one to classify

them as true high performance, high temperature stable low-k polymers. Therefore, it is

hoped that in the near future, the chemistry of these fluoro-polyimides would continue to

expand further to the forefront of polyimide science and become a focus of the

commercial high temperature materials research and development work worldwide. In

288

last four and half years, my PhD research work has been published in parts as two book

chapter, three international refereed journal papers, and four conference papers. The list

is given in this thesis.

5.2. Recommendations:

Over the past 60 years, polyimide chemistry has matured enough and the world has

witnessed a remarkable development in structural material technologies based on various

polyimides. Newer polyimide based nonmetallic materials such as polyimide/ceramics

polyimide/state-of-the-art material fibers, and polyimide/inorganic clay matrix

composites would continue replacing metal in a wide variety of industrial, aerospace and

consumer applications, ranging from highly specialized spacecraft structural

components, cryogenic rocket engines, cutting tools to tennis rackets. For the matrix

materials based high-temperature high performance structural composites component

made for applications in aerospace, and the materials for high-temperature stable low-k

dielectric applications for electronics industries, as well as long lasting and high

performance gas separation membrane fabrication applications, the fluoro-polyimides

(6F-PI), and specially the fluoro-poly(ether imide) (6F-PEI) polymers would be ideal

candidates for further investigations and application developments.

During this research, the knowledge developed on the (6F-PEI)s, (6F-CoPEI)s

polymers is very valuable. Understanding of their structure-properties relation ship was

established, and on the basis of which there exists a scope for their further industrial

applications development. Therefore, it is recommended that the following electronics

and microelectronics applications of these fluoro-poly(ether imide) (6F-PEI) materials

could be developed by several enterprising commercial companies under joint R&D

collaboration projects:

o Package encapsulant

289

o Base resin for photosensitive resist formulation

o Under-fill adhesives

o Interlayer protective (dielectric) coating

o Substrate for flexible circuit

Also in the field of fluoro-polyimide/inorganic compound nanocomposites materials

based on current R&D, a significant advancement would take place in the development

of newer ‘Ceramers’ along with the exploitation of new and state-of-the-art reinforcing

materials, such as, single walled carbon nanotubes (CSWNT), boron nanotubes (BNT),

for the commercial development of their newer industrial applications. Host of

technologies could also be developed in the field of its manufacturing and

processing/fabrication, to support the newer applications that would emerge.

For example in :

• Aerospace and aviation, maritime ship building, locomotives as well as

automotive, and engineering, etc. industries:

o Stronger light weight, and high temperature stable pre-fabricated main frame

structural components and/or engineering part made from these materials

would provide grater values and advantages in terms of performance to

weight ratio for high performance application for these industries.

o High temperature stable electrical insulators for power plant electro-magnates

o Engineering abrasion materials

• Electronics industries

o Molding compounds as well as thermally stable alpha particle shielding film

• Life science industries

o Materials for medical device and sensors fabrication

o Substrate materials to grow bio-enzymes or proteins molecules.

290

• Separation membranes industries

o Fabrication of gas separation module

• Fuel cell industries

o barrier membranes

291

APPENDIX - A

SYNTHESIS OF POLYIMIDE POLYMERS

292

APPENDIX - A: A-1. POLYMER SYNTHESIS

A-2. Synthesis of fluoro-poly(ether imide)s

Three additional fluoro-poly(ether imide)s (6F-PEI) were synthesized as per the

reaction scheme given in Figure 1.

A-2.1. Reaction scheme of synthesis of fluoro-poly(ether imide) (6F-PEI)

OC C

CCF3

O

O

O

C C

CCF3

O

O

OH

C C

CCF3

O

O

N

+

n

n

[6FDA + Diether Diamin] Fluoro-poly(ether amic acid) (6F-PEAA)


POLYMERIZATION

6FDA (Di-ether linked diamine)



[6FDA + Diether Diamine] Fluoro-poly(ether imide) polymer (6F-PEI)

CF3

CF3

CF3

C

C

O

O

N

C

C

O

O

O

C

C

O

O

HO

HN

HN

X OH2N NH2

O X O

O X O

C

CH3

CH3

C

CF3

CF3

S

O

O, ,

ORWHERE =

Figure-1 : Reaction scheme of synthesis of fluoro-poly(ether imide) (6F-PEI)

A-2.1.2 Synthesis of [6FDA + p-SED] fluoro-poly(ether imide) polymer

In the case of synthesis of [6FDA + p-SED], a (6F-PEI) based on 2,2-bis(3,4-

dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and 4,4-bis(4-aminophenoxy)

diphenyl sulfone (p-SED), the following materials and quantities (Table 1) were

employed .

293

Table-1 : Monomers and chemicals used for the synthesis of [6FDA + p-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.884 p-SED 432.50 100 0.02 8.65 NMP (@ 20 % solid NV) 70.15 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.024 2.45 Methanol 2000 ml

Procedure:

Accurately weighed 8.884g (0.02mole) of solid 6FDA was added to an equimolar

amount of m-SED diamine (8.65g) pre-dissolved in freshly distilled NMP to make 20 %

solid concentration. The reaction mixture was stirred under nitrogen at room temperature

for over 8 hours to make (6F-PEAA) solution, which was then chemically imidized to

form (6F-PEI).

SO

O

OOC

C

C

C

CF3

O O

O

N

C

O

CF3

N

n

[6FDA + p-SED] Fluoro-poly(ether imide) (6F-PEI) A-2.1.3. Synthesis of [6FDA + BPADE] fluoro-poly(ether imide) polymer In the case of synthesis of [6FDA + BPADE], which is a (6F-PEI) based on 2,2-

bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and 2,2-bis[4-(4-

aminophenoxy) phenyl] propane (BPADE), the above procedure was repeated and the

following materials and quantities (Table 2) were employed.

Table-2 : Monomers and chemicals used for the synthesis of [6FDA + BADE] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.884 BPADE 410.52 100 0.02 8.2104 NMP (@ 20 % solid NV) 68.38 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.024 2.45 Methanol 2000 ml

294

C

CH3

OOC

C

C

C

CF3

O O

O

N

C

O

CF3

N

n

[6FDA + BPADE] Fluoro-poly(ether imide) (6F-PEI)

CH3

A-2.1.4. Synthesis of [6FDA + BDAF] fluoro-poly(ether imide) polymer

In the case of synthesis of [6FDA + BDAF], which is a (6F-PEI) based on 2,2-bis(3,4-

dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and 2,2-bis[4-(4-

aminophenoxy) diphenyl] hexafluoropropane (BDAF)), the above procedure was

repeated and the following materials and quantities (Table 3) were employed.

Table-3 : Monomers and chemicals used for the synthesis of [6FDA + BDAF] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.8840 BDAF 518.463 100 0.02 10.3693 NMP (@ ~20 % solid NV) 77.013 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000 ml

C OOC

C

C

C

CF3

O O

O

NC

O

N

n

[6FDA + BDAF] Fluoro-poly(ether imide) (6F-PEI)

CF3CF3

CF3

A-2.2. Synthesis of non-fluorinate poly(ether imide)s

Using the above procedure 15 additional non-fluorinated poly(ether imide)s were

synthesized as per the reaction scheme is given in Figure 2.

295

A-2.2.1. Reaction scheme of synthesis of poly(ether imide)s (PEI)

Figure -2 : Reaction scheme of synthesis of poly(ether imide)s (PEI)

A-2.2.2. Synthesis of [PMDA + m-SED] poly(ether imide) polymer

In the case of synthesis of [PMDA + p-SED], which is a non-fluorinated PEI based on


4,4-bis(3-aminophenoxy)diphenyl sulfone (m-SED), the above procedure was repeated

and the following materials and quantities (Table 4) were employed.

Table-4 : Monomers and chemicals used for the synthesis of [PMDA + m-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) PMDA 218.12 100 0.04 8.7248 m-SED 432.50 100 0.04 17.300 NMP (@ 20 % solid NV) 104.10 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.900 Methanol 3000 ml

C

O

CC

O

C

O O

O O

Y OONH2NH2

C

NH

CC

HN

C

O O

O O

Y OOOH

C

N

CC

N

C

O O

O O

Y OO

A +

Where Y = -SO2- , -C(CH3)2-, - C(CF3)2-

AHO

n

An

Poly(ether amic acid) PEAA

5 to 30% solid (NV) in NMPRT, 5 to 20 hr.POLYMERIZATION

DianhydrideDi-ether Linked Diamine

Base Catayst/ Acetic AnhydrideRT, 5 to 20 hr.(-2H2O)

IMIDIZATION

Poly(ether imide) Polymer (PEI)

296

S

O

OO

C C

C

O

O

N

n

O

O

NC

O

[PMDA + m-SED] Poly(ether imide) (PEI)

A-2.2.3. Synthesis of [PMDA + BPADE] poly(ether imide) polymer

In the case of synthesis of [PMDA +BPADE], which is a non-fluorinated PEI based on


2,2-bis[4-(4-aminophenoxy) phenyl] propane (BPADE), the above procedure was


Table-5 : Monomers and chemicals used for the synthesis of [PMDA + BADE] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) PMDA 218.12 100 0.04 8.7248 BPADE 410.52 100 0.04 16.4208 NMP (@ 20 % solid NV) 100.5824 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.900 Methanol 3000 ml

C

CH3

OOC C

C

O

O

N

n

CH3

O

NC

O

[PMDA + BPADE] Poly(ether imide) (PEI)

A-2.2.4.. Synthesis of [PMDA + BDAF] poly(ether imide) polymer

In the case of synthesis of [PMDA + BDAF], which is a fluorinated PEI based on

1,2,4,5-benzenetetracarboxylic dianhydride [i.e. pyromellitic dianhydride (PMDA] and

2,2-bis[4-(4-aminophenoxy) diphenyl] hexafluoropropane (BDAF), the above procedure

was repeated and the following materials and quantities (Table 6) were employed.

297

Table-6 : Monomers and chemicals used for the synthesis of [PMDA + BDAF] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) PMDA 218.12 100 0.04 8.7248 BDAF 518.463 100 0.04 20.7285 NMP (@ 20 % solid NV) 117.8533 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.900 Methanol 3000 ml

C

CF3

OOC C

C

O

O

N

n

CF3

O

NC

O

[PMDA + BDAF] Fluoro-poly(ether imide) (6F-PEI)

A-2.2.5. Synthesis of [BPDA + p-SED] poly(ether imide) polymer

In the case of synthesis of [BPDA + p-SED], which is a non-fluorinated PEI based on

3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA),and 4,4-bis(4-aminophenoxy)

diphenyl sulfone (p-SED), the above procedure was repeated and the following materials

and quantities (Table 7) were employed.

Table-7 : Monomers and chemicals used for the synthesis of [BPDA + p-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BPDA 294.22 100 0.04 11.7688 p-SED 432.50 100 0.02 17.300 NMP (@ 20 % solid NV) 116.2752 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.900 Methanol 3000 ml

S

O

OO

C

C

CO O

O

N

C

O

N

n

[BPDA + p-SED] Poly(ether imide) (PEI)

O

298

A-2.2.6. Synthesis of [BPDA + m-SED] poly(ether imide) polymer

In the case of synthesis of [BPDA + m-SED], which is a non-fluorinated PEI based on

3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA),and 4,4-bis(3-aminophenoxy)

diphenyl sulfone (m-SED), the above procedure was repeated and the following

materials and quantities (Table 8) were employed.

Table-8 : Monomers and chemicals used for the synthesis of [BPDA + m-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BPADA 294.22 100 0.04 11.7688 m-SED 432.50 100 0.04 17.300 NMP (@ 20 % solid NV) 116.2752 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.900 Methanol 3000 ml

S

O

OO

C

C

CO O

O

N

C

O

N

n

[BPDA + m-SED] Poly(ether imide) (PEI)

O

A-2.2.7. Synthesis of [BPDA + BPADE] poly(ether imide) polymer

In the case of synthesis of [BPDA + BPADE], which is a non-fluorinated PEI based

on 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA),and 2,2-bis[4-(4-aminophenoxy)

phenyl] propane (BPADE), the above procedure was repeated and the following


Table-9 : Monomers and chemicals used for the synthesis of [PMDA + BADE] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BPDA 294.22 100 0.04 11.7688 BPADE 410.52 100 0.04 16.4208 NMP (@ 20 % solid NV) 112.7584 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.900 Methanol 3000 ml

299

C

CH3

OO

C

C

CO O

O

N

C

O

N

n

[BPDA + BPADE] Poly(ether imide) (PEI)

CH3

A-2.2.8. Synthesis of [BPDA + BDAF] poly(ether imide) polymer

In the case of synthesis of [BPDA + BDAF], which is a fluoro-PEI based on 3,3,4,4-

biphenyltetracarboxylic dianhydride (BPDA), and 2,2-bis[4-(4-aminophenoxy) diphenyl]

hexafluoropropane (BDAF), the above procedure was repeated but the following


Table-10 : Monomers and chemicals used for the synthesis of [BPDA + BDAF] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BPDA 294.22 100 0.04 11.7688 BDAF 518.463 100 0.04 20.7385 NMP (@ 20 % solid NV) 130.0293 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~10% extra) 102.09 0.048 4.900 Methanol 3000 ml

C

CF3

OO

C

C

CO O

O

N

C

O

N

n

[BPDA + BDAF] Fluoro-poly(ether imide) (6F-PEI)

CF3

A-2.2.9. Synthesis of [BTDA + p-SED] poly(ether imide) polymer

In the case of synthesis of [BTDA + p-SED], which is a non-fluorinated PEI based on

3,3,4,4-benzophenone tetracarboxylic dianhydride (BTDA), and 4,4-bis(4-

aminophenoxy) diphenyl sulfone (p-SED), the above procedure was repeated and the


300

Table-11 : Monomers and chemicals used for the synthesis of [BTDA + p-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BTDA 322.23 100 0.02 6.4446 p-SED 432.50 100 0.02 8.6500 NMP (@ 20 % solid NV) 60.3784 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000 ml

S

O

OOC C

C

CO O

O

N

C

O

N

n

OO

[BTDA + p-SED] Poly(ether imide) (PEI)

A-2.2.10. Synthesis of [BTDA + m-SED] poly(ether imide) polymer

In the case of synthesis of [BTDA + m-SED], which is a non-fluorinated PEI based on

3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA), and 4,4-bis(3-

aminophenoxy) diphenyl sulfone (m-SED), the above procedure was repeated and the


Table-12 : Monomers and chemicals used for the synthesis of [BTDA + m-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BTDA 322.23 100 0.02 6.4446 m-SED 432.50 100 0.02 8.6500 NMP (@ 20 % solid NV) 60.3784 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000 ml

S

O

OO

C C

C

CO O

O

N

C

O

N

n

O

O

[BTDA + m-SED] Poly(ether imide) (PEI)

301

A-2.2.11.. Synthesis of [BTDA + BPADE] poly(ether imide) polymer

In the case of synthesis of [BTDA + BPADE], which is a non-fluorinated PEI based

on 3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA), and 2,2-bis[4-(4-

aminophenoxy) phenyl] propane (BPADE), the above procedure was repeated and the


Table-13 : Monomers and chemicals used for the synthesis of [BTDA + BADE] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BTDA 322.23 100 0.02 6.4446 BPADE 410.52 100 0.02 8.2104 NMP (@ 20 % solid NV) 58.62 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.024 2.45 Methanol 2000 ml

C

CH3

OOC C

C

CO O

O

N

C

O

N

n

CH3O

[BTDA + BPADE] Poly(ether imide) (PEI)

A-2.2.12. Synthesis of [BTDA + BDAF] poly(ether imide) polymer

In the case of synthesis of [BTDA + BDAF], which is a fluoro PEI based on 3,3,4,4-

benzophenonetetracarboxylic dianhydride (BTDA), and 2,2-bis[4-(4-aminophenoxy)

diphenyl] hexafluoropropane (BDAF), the above procedure was repeated and the


Table-14 : Monomers and chemicals used for the synthesis of [BTDA + BDAF] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) BTDA 322.23 100 0.02 6.4446 BDAF 518.463 100 0.02 10.3693 NMP (@ 20 % solid NV) 67.2554 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.02 2.246 Methanol 2000 ml

302

C

CF3

OOC C

C

CO O

O

N

C

O

N

n

CF3O

[BTDA + BDAF] Fluoro-poly(ether imide) (6F-PEI)

A-2.2.13. Synthesis of [ODPA + p-SED] poly(ether imide) polymer

In the case of synthesis of [ODPA + p-SED], which is a non-fluorinated PEI based on

bis(3,4-dicarboxyphenyl) ether dianhydride, [i.e. 4,4-oxydiphthalic anhydride (ODPA)],

and 4,4-bis(4-aminophenoxy) diphenyl sulfone (p-SED), the above procedure was


Table-15 : Monomers and chemicals used for the synthesis of [ODPA + p-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) ODPA 310.20 100 0.02 6.204 p-SED 432.5 100 0.02 8.6500 NMP (@ 20 % solid NV) 58.816 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.024 2.45 Methanol 2000 ml

S

O

OOO C

C

CO O

O

N

C

O

N

n

O

[ODPA + p-SED] Poly(ether imide) (PEI)

A-2.2.14. Synthesis of [ODPA + m-SED] poly(ether imide) polymer

In the case of synthesis of [ODPA + m-SED], which is a non-fluorinated PEI based on

bis(3,4-dicarboxyphenyl) ether dianhydride, [i.e. 4,4-oxydiphthalic anhydride (ODPA)],

and 4,4-bis(3-aminophenoxy) diphenyl sulfone (m-SED), the above procedure was

repeated but the following materials and quantities (Table 16) were employed.

303

Table-16 : Monomers and chemicals used for the synthesis of [ODPA + m-SED] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 310.20 100 0.02 6.204 m-SED 432.50 100 0.02 8.6500 NMP (@ 20 % solid NV) 58.816 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.024 2.45 Methanol 2000 ml

S

O

OO

O C

C

CO O

O

N

C

O

N

n

O

[ODPA + m-SED] Poly(ether imide) (PEI)

A-2.2.15. Synthesis of [ODPA + BPADE] poly(ether imide) polymer

In the case of synthesis of [ODPA + BPADE], which is a non-fluorinated PEI based

on bis(3,4-dicarboxyphenyl) ether dianhydride, [i.e. 4,4-oxydiphthalic anhydride

(ODPA)], and 2,2-bis[4-(4-aminophenoxy) phenyl] propane (BPADE), the above

procedure was repeated and the following materials and quantities (Table 17) were

employed.

Table-17 : Monomers and chemicals used for the synthesis of [ODPA + BPADE] polymer

Chemical/Monomer Mol.

Wt. Mole %

Mol. Wt. (g)

ODPA 310.20 100 0.02 6.204 BPADE 410.52 100 0.02 8.2104 NMP (@ 20 % solid NV) 57.6576 β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~20% extra) 102.09 0.024 2.45 Methanol 2000 ml

C

CH3

OOO C

C

CO O

O

N

C

O

N

n

CH3

[ODPA + BPADE] Poly(ether imide) (PEI)

304

A-2.2.16. Synthesis of [ODPA + BDAF] poly(ether imide) polymer In the case of synthesis of [ODPA + BDAF], which is a fluoro PEI based on bis(3,4-

dicarboxyphenyl) ether dianhydride, [i.e. 4,4-oxydiphthalic anhydride (ODPA)], and 2,2-

bis[4-(4-aminophenoxy) diphenyl] hexafluoropropane (BDAF), the above procedure was


Table-18 : Monomers and chemicals used for the synthesis of [ODPA + BDAF]

Chemical/Monomer Mol. Wt.

Mole %

Mol. Wt. (g)

ODPA 310.20 100 0.02 BDAF 518.463 100 0.02 NMP (@ 20 % solid NV) β-Picoline 93.13 0.04 3.725 Acetic Anhydride( ~10% extra) 102.09 0.02 2.246 Methanol

C

CF3

OOO C

C

CO O

O

N

C

O

N

n

CF3

[ODPA + BDAF] Fluoro-poly(ether imide) (6F-PEI)

A-2.3. Synthesis of fluorinated copoly(ether imide) (6F-CoPEI) polymers

Two series of random fluoro-copoly(ether imide) [6FDA + (n Mole) p-SED + (m Mole)

Di-ether diamine monomer] (6F-PEI) were synthesized by reacting equimolar amount of

2,2-bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) with a mixture

diether diamines, such as, a mixture of 4,4-bis(3-aminophenoxy) diphenyl sulfone (p-

SED) and 2,2-bis[4-(4-aminophenoxy) phenyl] propane (BPADE), or a mixture of 4,4-

bis(3-aminophenoxy) diphenyl sulfone (p-SED) and 2,2-bis[4-(4-aminophenoxy)

diphenyl] hexafluoropropane (BDAF).

305

A-3.1. Reaction scheme of synthesis of fluoro-copoly(ether imide) (6F-CoPEI)

S OONH2NH2

Where Y = -C(CH3)2-, - C(CF3)2-

n

Fluoro-CoPoly (ether-amic Acid)

5 to 30% NV, NMPRT

6FDADiether Linked Diamine

Base Catalyst/ Acetic AnhydrideRT

IMIDIZATION

Fluoro-CoPoly (ethe-rimide) Polymer

CC

C

C

CF3

O O

O

OC

O

+

CF3

O Y OONH2NH2+

n Mole %

O

O

CC

C

HC

CF3

O O

O

HN

C

O

CF3

S OO

O

O

OHHN

CC

C

C

CF3

O O

O

HNC

O

CF3OH

HN

HO

Y OOm

CC

C

C

CF3

O O

O

NN

C

O

CF3

CC

C

C

CF3

O O

O

NC

O n

CF3

N

m

SED

m Mole %

Y OOS OO

O

O

Figure-3 : Synthesis reaction scheme for [6FDA + (n Mole) p-SED + (m Mole) Di-ether diamine] fluoro-copoly(ether imide)

A-3.2.1. Series-1: Synthesis of [6FDA + (n Mole%) p-SED + (m Mole%) BPADE] fluoro-copoly(ether imide) polymer

For series-1, two additional fluoro-copoly(ether imide)s were synthesized as per


A-3.2.1.1. Synthesis of [6FDA + (50%) p-SED + (50%) BPADE] fluoro-

copoly(ether imide) polymer In the case of synthesis of [6FDA + (50%) p-SED + (50%) BPADE] which is a fluoro-

copoly(ether imide) based on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane

dianhydride (6FDA) and a mixture of 4,4-bis(3-aminophenoxy) diphenyl sulfone (p-

SED) and 2,2-bis[4-(4-aminophenoxy) phenyl] propane (BPADE) the above procedure

was repeated and the following materials and quantities (Table 19) were employed.

306

Table-19 : Monomers and chemicals used for the synthesis of [6FDA + (50%) p-SED + (50%) BPADE copolymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.8840 p-SED 432.5 50 0.01 4.3250 BPADE 410.52 50 0.01 4.1052 NMP (@ 20 % solid NV) 69.2568 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000 ml

C C

C

C

CF3

O O

O

NNCO

CF3

Fluoro-copoly(ether imide): [ 6FDA + (50%) p-SED + (50%) BPADE ] (6F-CoPEI)

0.50

C

CH3

OO

CH3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.50

O

A-3.2.1.2. Synthesis of [6FDA + (25%) p-SED + (75%) BPADE] fluoro- copoly(ether imide) polymer

In the case of synthesis of [6FDA + (25%) p-SED + (75%) BPADE] which is a fluoro-



SED) and 2,2-bis(4-aminophenoxy) phenyl] propane (BPADE), the above procedure was


Table-20 : Monomers and chemicals used for the synthesis of [6FDA + (25%) p- SED + (75%) BPADE] copolymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.8840 p-SED 432.5 25 0.005 2.1625 BPADE 410.52 75 0.015 6.1578 NMP (@ 20 % solid NV) 68.8172 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000 ml

C C

C

C

CF3

O O

O

NNCO

CF3


0.25

C

CH3

OO

CH3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.75

O

307

A-3.2.2. Series-2: Synthesis of [6FDA + (n Mole%) p-SED + (m Mole%) BDAF]

fluoro-copoly(ether imide) polymer For Series-2, two additional fluoro-copoly(ether imide)s were synthesized as per the


A-3.2.2.1. Synthesis of [6FDA + (50%) p-SED + (50%) BDAF] fluoro- copoly(ether imide) polymer

In the case of synthesis of [6FDA + (50%) p-SED + (50%) BDAF] which is a fluoro-



SED) and 2,2-bis[4-(4-aminophenoxy) diphenyl] hexafluoropropane (BDAF), the above


employed.

Table-21 : Monomers and chemicals used for the synthesis of [6FDA + (50%) p-SED + (50%) BDAF] copolymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.8840 p-SED 432.50 50 0.01 4.3250 BDAF 518.463 50 0.01 5.1846 NMP (@ 20 % solid NV) 73.5744 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000 ml

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.50

C C

C

C

CF3

O O

O

NNCO

CF3

C

CF3

OO

CF30.50

Fluoro-copoly(ether imide): [ 6FDA + pSED (50 %) + BDAF (50 %) ] (6F-CoPEI)

O

308

A-3.2.2.2. Synthesis of [6FDA + (25%) p-SED + (75%) BDAF] fluoro- copoly(ether imide) polymer

In the case of synthesis of [6FDA + (25%) p-SED + (75%) BDAF] which is a fluoro-



SED) and 2,2-bis[4-(4-aminophenoxy) diphenyl] hexafluoropropane (BDAF)), the above


employed.

Table-22 : Monomers and chemicals used for the synthesis of [6FDA + (25%) p-SED + (75%) BDAF] copolymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.02 8.8840 p-SED 432.5 25 0.005 2.1625 BDAF 518.463 75 0.015 7.7770 NMP (@ 20 % solid NV) 75.2940 β-Picoline 93.13 0.04 3.7250 Acetic Anhydride( ~20% extra) 102.09 0.024 2.4500 Methanol 2000 ml

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.25

C C

C

C

CF3

O O

O

NNCO

CF3

C

CF3

OO

CF30.75

Fluoro-copoly(ether imide): [ 6FDA +(25%) p-SED + (75%) BDAF ] (6F-CoPEI)

O

A-3.3. Synthesis of polyimides and copolyimides for electrical properties studies

Additionally, one non-fluorinated polyimide (PI), four fluoro-polyimides (6F-PI), and

two fluoro-copolyimides (6F-CoPI) of interest were selected and synthesized as per the

respective synthesis schemes given in Figures 4 to 6 for the purpose of studying their

dielectric properties, i.e. measuring mostly dielectric constant values. Comparison was

made between their estimated dielectric constants and the experimentally determined as

well as literature cited values. Similarly, comparison was also made on the

experimentally determined dielectric constant values of the fluorinated poly(ether

imide)s (6F-PEI) and copoly(ether imide)s (6F-CoPEI) synthesized.

309

A-3.3.1. Synthesis of poly(amic acid) (PAA)

Some high molecular polyimide structures in their fully imidized form are insoluble in

dipolar aprotic solvents and precipitate out as solid powder during high temperature

solution imidization or room temperature chemical imidization reaction. Hence, in such

polyimide structures, their precursor, i.e., poly(amic acid) solutions are always used in

fabricating useful forms. Thermal imidization is the only way to convert into fully

imidized polyimide structures. One additional polymer was synthesized as per the


A-3.3.1.A. Synthesis reaction scheme

Z OO


, etc.

AC

OCC

OC

O O

O O

Where A = OR X


Aromatic Dianhydride (1 Mol)

H2N A1 NH2+

AC

OHCCHO

C

O O

O O

HN A1

HN

AC

CC

C

O O

O O

N A1N

n

n

POLYMERIZATION20% NV,NMPRT

Aromatic Diamine (1 Mol)

Z OO

Where Y = Single bond, -CH2-, -O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

, etc.

Where A1 = OR Y

-Si(CH3)2-O-Si(CH3)2-,Where Z = X

Where Z = Y

POLYIMIDE

THERMAL IMIDIZATION

POLY(AMIC ACID)

CH3H3C

H3C CH3

CH3

H3C

OR

-2H2O

Figure -4 : Reaction scheme for synthesizing poly(amic acid)

310

A-3.3.1.2. Synthesis of [PMDA +3,3-ODA] poly(amic acid) (PAA)

In the case of [PMDA + 3,3-ODA] poly(amic acid) which is based on 1,2,4,5

benzenetetracarboxylic anhydride, i.e., pyromellitic dianhydride (PMDA) and 3,3-

oxydianiline using the above procedure and the following materials and quantities (Table

23) were employed.

Table-23 : Monomers and chemicals used for the synthesis of [PMDA + 3,3-ODA] poly(amic acid)

Chemical/Monomer Mol.

Wt. Mole %

Mol. Wt. (g)

PMDA 218.12 100 0.08 17.4496 3,3’-ODA 200.24 100 0.08 16.0192 NMP (@ 20 % solid NV) 133.8752

A-3.3.1.2. A. Synthesis procedure

Accurately weighed 17.4496g (0.08mole) of solid PMDA was added to an equimolar

amount of 3.3’-ODA diamine (16.0192g) pre-dissolved in freshly distilled NMP to make

20 % solid concentrations. The reaction mixture was stirred under nitrogen at room

temperature for over 8 hours to make poly(amic acid) (PEAA) solution, which was then

stored in a polypropylene (PP) bottle in refrigerator until used to cast film.

C

C C

C

NH

NH O

O

O

O

O n

[PMDA + 3,3-ODA] Poly(amic acid) (PAA)

OHHO

A-3.3.2. Synthesis of fluoro-polyimide (6F-PI)

Four additional fluoro-polyimides (6F-PI) of interest were synthesized as per the

synthesis schemes given in Figure 5.

311

A-3.3.2.1. Synthesis reaction scheme for fluoro-polyimide (6F-PI)

NH2 R

5 to 30% NV, NMPRT

6FDA

Base Catalyst / Acetic Anhydride-2H2O

Fluoro-polyimide Polymer [6F-PI]

CC

C

C

CF3

O O

O

OC

CF3

+

n Mole

CC

C

C

CF3

O O

O

HN

C

O

CF3OH

RHN

CC

C

C

CF3

O O

O

NC

CF3

n

Aromatic Diamine

POLYMERIZATION

HO

n MoleO

Y OO

X Where X = Single bond, -CH2-, -O-, -S- , -SO2- , -C(CH3)2-, -C(CF3)2-, -CO-, -C(CF3)Ph-,

etc.

Where R = OR


Where Z = Y

NH2

R

n

Fluoro-poly(amic acid) [6F-PAA]

O

N

O

CH3H3C

H3C CH3

OR

CH3

H3C


Figure-5 : Synthesis reaction scheme for fluoro-polyimide (6F-PI)

A-3.3.2.2. Synthesis of [6FDA + p-PDA] fluoro-polyimide polymer

[6FDA + p-PDA] is based on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane

dianhydride (6FDA) and 1, 4- phenylenediamine (p-PDA) was synthesized using the

above procedure and the following materials and quantities (Table 24) were employed.

312

Table-24 : Monomers and chemicals used for the synthesis of [6FDA + p-PDA] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (gm) 6FPA 444.20 100 0.12 53.304 p-PDA 108.143 100 0.12 12.98 NMP (@ 20 % solid NV) 265.136 β-Picoline 93.13 0.48 44.70 Acetic Anhydride (~10% extra) 102.09 0.264 26.952 Methanol 12,000

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

n

[6FDA + p-PDA] Fluoro-polyimide (6F-PI)

A-3.3.2.3. Synthesis of [6FDA +1,4-Diamino Durene] fluoro-polyimide polymer

[6FDA + 1,4-Diamino Durene] based on 2,2-bis(3,4-dicarboxyphenyl)

hexafluropropane dianhydride (6FDA) and 2,3,5,6-tetramethyl-1-4-phenylenediamine

(Durene diamine) was synthesized using the above procedure and the following materials

and quantities (Table 25) were employed.

Table-25 : Monomers and chemicals used for the synthesis of [6FDA + 1,4-Diamino Durene] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.12 53.304 1,4-Diamino Durene 164.25 100 0.12 19.71 NMP (@ 20 % solid NV) 292.04 β-Picoline 93.13 0.48 44.70 Acetic Anhydride (~10% extra) 102.09 0.264 26.952 Methanol 12,000 ml

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

n

CH3

CH3H3C

H3C

[6FDA + 1,4-Diamino Durene] Fluoro-polyimide (6F-PI)

313

A-3.3.2.4. Synthesis of [6FDA +4,4-ODA] fluoro-polyimide polymer

[6FDA + 4,4-ODA] is based on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane

dianhydride (6FDA) and 4,4-oxydianiline (4,4-ODA) was synthesized using the above

procedure and the following materials and quantities (Table 26) employed.

Table-26 : Monomers and chemicals used for the synthesis of [6FDA + 4,4-ODA] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.04 17.768 4,4-ODA 200.24 100 0.04 8.0096 NMP (@ 20 % solid NV) 103.11 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride (~20% extra) 102.09 0.048 4.901 Methanol 4000 ml

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

On

[6FDA + 4,4-ODA] Fluoro-polyimide (6F-PI)

A-3.3.2.5 Synthesis of [6FDA + 4,4-6F-Diamine] fluoro-polyimide polymer

[6FDA + 4,4-6F-Diamine], based on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane

dianhydride (6FDA) and 2,2-bis(4-aminophenyl) hexafluoropropane, (4,4-6F diamine)

was synthesized using the above procedure and the following materials and quantities

(Table 27) were employed.

Table-27 : Monomers and chemicals used for the synthesis of [6FDA + 4,4-6F- Diamine] polymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (gm) 6FDA 444.20 100 0.10 44.20 4,4-6F-Diamine 334.2642 100 0.10 33.42642 NMP (@ 20 % solid NV) 311.39 β-Picoline 93.13 0.20 18.626 Acetic Anhydride( ~20% extra) 102.09 0.12 12.2508 Methanol 10,000

314

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

C

CF3

CF3n

[6FDA + 4,4-6F-Diamine] Fluoro-polyimide (6F-PI)

A-3.3.3. Synthesis of fluoro-copolyimide (6F-CoPI)

Three fluoro-copolyimide were also synthesized as per the synthesis scheme given in

Figure 6 for dielectric properties comparison purpose only.

A-3.3.3.1. Synthesis reaction scheme for fluoro-copolyimide (6F-CoPI)

NH2 A

5 to 30% NV, NMPRT

6FDA


Fluoro-copolyimide polymer (6F-CoPI)

CC

C

C

CF3

O O

O

OC

CF3

+

(m1 Mole %)

CC

C

C

CF3

O O

O

HN

C

O

CF3OH

AHN

Aromatic Diamine

POLYMERIZATION

HO

(n Mole %)O

Y OO

X


, etc.

Where A = OR


Where Z = Y

NH2

m1

Fluoro-copoly(amic acid) (6F-CoPAA)

O NH2 B

(m2 Mole %)Aromatic Diamine

NH2+

[ m1 + m2 = n ]

CC

C

C

CF3

O O

O

HN

C

O

CF3OH

BHN

HO

m2

CC

C

C

CF3

O O

O

NC

O

CF3

AN CC

C

C

CF3

O O

O

NC

O

CF3

BN

m1m2

Y OO

X


, etc.

Where B = OR


Where Z = Y

CH3H3C

H3C CH3

OR

Figure-6 : Synthesis reaction scheme for fluoro-copolyimide (6F-CoPI)

315

A-3.3.3.2. Synthesis of [6FDA + (50%) 1,4-Diamino Durene + (50%) p- PDA] fluoro-copolyimide polymer [6FDA + (50%) 1,4-Diamino Durene + (50%) p-PDA] Copolyimide based on 2,2-

bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and a mixture of 50

mole % of 1,4-phenylenediamine (p-PDA) and 50 mole% 2,3,5,6-tetramethyl-1-4-

phenylenediamine (Durene diamine) was synthesized using the above procedure and the


Table-28 : Monomers and chemicals used for the synthesis of [6FDA + (50%) p-PDA+ (50%) 1,4-Diamino Durene] copolymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.04 17.768 p-PDA 108.143 50 0.02 2.1629 1,4-Diamino Durene 164.25 50 0.02 3.285 NMP (@ 20 % solid NV) 92.864 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.901 Methanol 4000 ml

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

5050

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

H3C CH3

H3C CH3

[6FDA + (50%) 1,4-Diamino durene + (50%) p-PDA] Fluro-copolyimidee (6F-CoPI)

A-3.3.3.3. Synthesis of [6FDA + (50%) 1,4-Diamino Durene + (50%) m-PDA]

fluoro-copolyimide polymer [6FDA + 50 mole% 1,4-Diamino Durene + 50 mole% m-PDA] Copolyimide is based

on 2,2-bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and a mixture of

50 mole % of 1,3-phenylenediamine (m-PDA) and 50 mole% 2,3,5,6-tetramethyl-1-4-

phenylenediamine (Durene diamine) was synthesized using the above procedure and the


316

Table-29 : Monomers and chemicals used for the synthesis of [6FDA + (50%) m-PDA+ (50 %) 1,4-Diamino Durene] copolymer

Chemical/Monomer Mol. Wt. Mole % Mol. Wt. (g) 6FDA 444.20 100 0.04 17.768 m-PDA 108.143 50 0.02 2.1629 1,4-Diamino Durene 164.25 50 0.02 3.285 NMP (@ 20 % solid NV) 92.864 β-Picoline 93.13 0.08 7.4504 Acetic Anhydride( ~20% extra) 102.09 0.048 4.901 Methanol 4000 ml

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

5050

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

H3C CH3

H3C CH3

[6FDA + (50%) 1,4-Diamino durene + (50%) m-PDA] Fluro-copolyimide (6F-CoPI)

317

APPENDIX – B

ESTIMATION OF DIELECTRIC CONSTANTS (ε′) OF POLYIMIDES

POLYMERS

318

APPENDIX – B:

ESTIMATION OF DIELECTRIC CONSTANT (ε′) OF POLYIMIDES POLYMERS

B-1. Non-fluorinated Polyimide Polymers B-1.1. Estimation of dielectric constant of [ODPA + m-Tolidine] polyimide

C

C C

CO

O

O

N

O

O

N

CH3

H3Cn

[ODPA + m-Tolidine] Polyimide (PI)



2

C

O

NCO

2x 51.28

2x108.50 2x276.59 2x 145.10

2

2x 25.00

2x 65.50 2x 128.60 2x 76.10

1 - O -

1x 5.20

1x 8.50 1x 30.00 1x 16.00

2 – CH3

2x 5.64

2x 23.00 2x 17.66 2x 15.03

∑ 169.04 402.50 875.70 488.46

Now using Lorentz and Lorenz’s and Vogel’s equations (10) and (11) respectively

LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [ODPA + m-Tolidine] at 1 kHz

ε′ = (2x169.04 + 402.50) ÷ 402.50-169.04) = 3.17 by eq. (10)

ε′ = (875.70 ÷ 488.46)2 = 3.22 by eq. (11)

EXPERIMENTAL Value : ε′ = 3.48 (at 1 kHz),

319

B-1.2. Estimation of dielectric constant of [PMDA + 3,3-ODA] polyimide

C

C C

C

N N O

O

O

O

O

n

[PMDA + 3,3-ODA] Polyimide (PI)



1 C

C C

CN N

O

O

O

O

1x 76.845

2x 151.00 1x 428.02 1x 214.10

2

2x 25.00

2x 69.00 2x128.60 2x 76.10

1 - O -

1x 5.20

1x 8.50 1x 30.00 1x 16.00

∑ 132.045 297.50 715.22 382.30


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [PMDA + 3,3-ODA] at 1 kHz

ε′ = (2x132.045 + 297.50) ÷ 297.50-132.045) = 3.39 by eq. (10)

ε′ = (715.22 ÷ 382.30)2 = 3.50 by eq. (11)

EXPERIMENTAL Value : ε′ = 3.42 (at 1 kHz),

320

B-1.3. Estimation of dielectric constant of [BPDA + m-PDA] polyimide

n

CO

NCO

CO

NCO

[ BPDA + m-PDA ] Polyimide (PI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

1

1x 25.00

1x 69.00 1x 128.60 1x 76.10

∑ 127.56 286.00 681.60 366.30


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [BPDA + m-PDA] at 1 kHz

ε′ = (2x127.56 + 286.00) ÷ 286.00 - 127.56) = 3.415 by eq. (10)

ε′ = (6810.60 ÷ 366.30)2 = 3.205 by eq. (11)

LITERATURE Value : ε′ = 3.50 (at 1 kHz)*

EXPERIMENTAL Value : ε′ = 3.47 (at 1 kHz), * : Chapter 3, Reference # [33]

321

B-1.4. Estimation of dielectric constant of UPLIEXR [BPDA + 4,4-ODA] polyimide

O

nC

O

N

C

O

C

O

NCO

UPILEX-R [ BPDA + 4,4-ODA] Polyimide (PI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

2

2x 25.00

2x 65.50 2x128.60 2x 76.10

1 - O -

1x 5.20

1x 8.5 1x 30.00 1x 16.00

∑ 157.76 356.5 840.38 458.40


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [BPDA + 4,4-ODA] at 1 kHz

ε′ = (2x157.76 + 356.5) ÷ 356.50-157.76) = 3.38 by eq. (10)

ε′ = (840.38 ÷ 458.40)2 = 3.36 by eq. (11)

LITERATURE Value : ε′ = 3.50 (at 1 MHz)*, * : Chapter 3, References # [22, 98]

322

B-2. Fluoro-polyimides B-2.1. Estimation of dielectric constant of [6FDA + m-PDA] fluoro-polyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

n

[6FDA + m-PDA] Fluoro-polyimide (6F-PI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

1

1x 25.00

1x 69.00 1x 128.60 1x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

∑ 146.16 359.44 888.18 516.30


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [6FDA + m-PDA] at 1 kHz

ε′ = (2x146.16 + 359.44) ÷ 359.44 - 146.16) = 3.056 by eq. (10)

ε′ = (888.18 ÷ 516.30)2 = 2.96 by eq. (11)

LITERATURE Value : ε′ = 3.00 (at 1 MHz)*,

EXPERIMENTAL Value : ε′ = 3.045 (at 1 kHz), * : Chapter 3, References # [33]

323

B-2.2. Estimation of dielectric constant of [6FDA + p-PDA] fluoro-polyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

n

[6FDA + p-PDA] Fluoro-polyimide (6F-PI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

1

1x 25.00

1x 65.50 1x 128.60 1x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

∑ 146.16 355.94 888.18 516.30


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [6FDA + p-PDA] at 1 kHz

ε′ = (2x146.16 + 355.94) ÷ 355.94-146.16) = 3.09 by eq. (10)

ε′ = (888.18 ÷ 516.30)2 = 2.96 by eq. (11)


EXPERIMENTAL Value : ε′ = 3.036 (at 1 kHz), 3.016 (at 10 MHz) * : Chapter 3, References # [33]

324

B-2.3. Estimation of dielectric constant of [6FDA + 1,4-Dimino Durene] fluoro- polyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

n

CH3

CH3H3C

H3C

6FDA + 1,4-Diamino Durene] Fluoro-polyimide (6F-PI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

1

1x 47.56

1x 151.5 1x 199.24 1x 134.20

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

∑ 168.74 441.94 958.76 574.40


LL

LL

PVVP

−+

=2

'ε (11)

2

'

=

MPVε (10)

We get values of dielectric constant ε′ for [6FDA + Durene Diamine] at 1 kHz

ε′ = (2x168.74 + 441.94) ÷ 441.94-168.74) = 2.85 by eq. (10)

ε′ = (958.76. ÷ 574.40)2 = 2.79 by eq. (11)



CH3

CH3H3C

H3C

325

B-2.4. Estimation of dielectric constant of [6FDA + 4,4-6F-Diamine] fluoro- polyimide



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

2

2x 25.00

2x 65.50 2x 128.60 2x 76.10

2 – C –

2x 2.60

2x 5.28 2x 26.40 2x 12.00

4 –CF3

4x 8.00

4x 34.08 4x 90.00 4x 69.00

∑ 189.76 491.88 1223.18 742.40


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [6FDA + 4,4-6F-Diamine] at 1 KHz

ε′ = (2x189.76 + 491.88) ÷ 491.88-189.76) = 2.88 by eq. (10)

ε′ = (1223.18 ÷ 742.40)2 = 2.72 by eq. (11)

LITERATURE Value : ε′ = 2.78 (at 1 MHz)*, 2.58 (at 10 MHz)*,


C

C C

C

O

N

O

C

CF3

CF3

O

N

O

C

CF3

CF3n

[6FDA + 4,4-6F-Diamine] Fluoro-polyimide (6F-PI)

326

B-2.5. Estimation of dielectric constant of [6FDA + 4,4-ODA] fluoro-polyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

On

[6FDA + 4,4-ODA] Fluoro-polyimide (6F-PI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

2

2x 25.00

2x 65.50 2x 128.60 2x 76.10

1 - O -

1x 5.20

1x 8.5 1x 30.00 1x 16.00

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 – CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

∑ 176.36 429.94 1046.78 608.40


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [6FDA + 4,4-ODA] at 1 kHz

ε′ = (2x176.36 + 429.94) ÷ 429.94-176.36) = 3.09 by eq. (10)

ε′ = (1046.78 ÷ 608.40)2 = 2.96 by eq. (11)



327

B-3. Fluoro-copolyimides B-3.1. Estimation of dielectric constant of [6FDA + (50%) m-PDA + (50%) p-PDA] fluoro-copolyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

50

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

50

[6FDA +(50%) p-PDA + (50%) m-PDA] Fluoro-copolyimide (6F-CoPI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

0.5 0.5x25.00

0.5x 65.50 0.5x 128.60 0.5x 76.10

0.5

0.5x25.00

0.5x 69.00 0.5x 128.60 0.5x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

∑ 146.16 357.69 888.18 516.30

Now using Vora-Wang’s equations (13) and (14) respectively

)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)

We get values of dielectric constant ε′ for [6FDA + (50%) m-PDA + (50%) p-PDA] at 1 kHz

ε′ = (2x146.16 + 357.69) ÷ 357.69 - 146.16) = 3.07 by eq. (13)

ε′ = (888.18 ÷ 516.30)2 = 2.96 by eq. (14)

EXPERIMENTAL Value : ε′ = 3.05 (at 1 kHz)

328

B-3.2. Estimation of dielectric constant of [6FDA + (50%) m-PDA + (50%) Durene Diamine] fluoro-copolyimide

C C

C

CH3C CH3

CH3H3C

CF3

O O

O

N

C

O

CF3

n

N

C C

C

CCF3

O O

O

N

C

O

CF3

N

m

[6FDA + (50%) 1,4 Diamino Durene + (50%) m-PDA] Fluoro-copolyimide (6F-CoPI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

0.5 0.5x 25.00

0.5x 69.00 0.5x 128.60 0.5x 76.10

0.5

0.5x 47.56

0.5x 151.5 0.5x 199.24 1x 134.20

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

∑ 157.44 400.69 923.50 545.35


)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)

We get values of dielectric constant ε′ for [6FDA + (50%) m-PDA + (50%) Durene Diamine] at 1 kHz

ε′ = (2x157.44 + 400.69) ÷ 400.69 - 157.44) = 2.94 by eq. (13)

ε′ = (923.5 ÷ 545.35)2 = 2.87 by eq. (14)


CH3

CH3H3C

H3C

329

B-3.3. Estimation of dielectric constant of [6FDA + (50%) p-PDA + (50%) Durene Diamine] fluoro-copolyimide

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

5050

C

C C

C

O

N

O

C

CF3

CF3

O

N

O

H3C CH3

H3C CH3

[6FDA + (50%) 1,4-Diamino Durene + (50%) p-PDA] Fluro-copolyimide (6F-CoPI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

0.5 0.5x 25.00

0.5x 65.50 0.5x128.60 0.5x 76.10

0.5

0.5x 47.56

0.5x 151.5 0.5x 199.24 1x 134.20

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

∑ 157.44 398.94 923.50 545.35


)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)

We get values of dielectric constant ε′ for [6FDA + (50%) p-PDA + (50%) Durene Diamine] at 1 kHz

ε′ = (2x157.44 + 398.94) ÷ 398.94 - 157.44) = 2.96 by eq. (13)

ε′ = (923.5.83 ÷ 545.35)2 = 2.87 by eq. (14)


CH3

CH3H3C

H3C

330

B-4. Fluoro-poly(ether imide)s B-4.1. Estimation of dielectric constant of [6FDA + p-SED] fluoro-poly(ether imide)

S

O

O

OOC

C

C

C

CF3

O O

O

N

C

O

CF3

N

n

[6FDA + p-SED] Fluoro-poly(ether imide) (6F-PEI)



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4

4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

1 – SO2–

1x 18.40

1x 32.50 1x 120.00 1x 64.06

∑ 249.96 608.94 1453.18 840.06


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [6FDA + p-SED] at 1 kHz

ε′ = (2x249.66 + 608.94) ÷ 608.94 - 249.66) = 3.09 by eq. (10)

ε′ = (1453.18 ÷ 840.66)2 = 2.99 by eq. (11)

LITERATURE Value : ε′ = 2.87 (at 1 MHz)*, ε′ = 2.74 (at 10 MHz)*

EXPERIMENTAL Value : ε′ = 3.10 (at 1 kHz) * : Chapter 3, References # [80]

331

B-4.2. Estimation of dielectric constant of [6FDA + BPADE] fluoro-poly(ether imide)

C

CH3

OOC

C

C

C

CF3

O O

O

N

C

O

CF3

N

n

[6FDA + BPADE] Fluoro-poly(ether imide) (6F-PEI)

CH3



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4

4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

1 CH3-C-CH3–

1x 13.90

1x 49.00 1x 61.00 1x 42.00

∑ 245.46 618.44 1395.68 818.60


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [6FDA + BPADE] at 1 kHz

ε′ = (2x245.46 + 618.44) ÷ 618.44 - 245.46) = 2.97 by eq. (10)

ε′ = (1395.68 ÷ 818.60)2 = 2.907 by eq. (11)

LITERATURE Value : ε′ = 2.65 (at 10 MHz)*

EXPERIMENTAL Value : ε′ = 3.04 (at 1 kHz)*, * : Chapter 3, References # [80]

332

B-4.3. Estimation of dielectric constant of [6FDA + BDAF] fluoro-poly(ether imide_

C OOC

C

C

C

CF3

O O

O

NC

O

N

n

[6FDA + BDAF] Fluoro-poly(ether imide) (6F-PEI)

CF3CF3

CF3



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4

4x 25.00

4x 65.50 4x 128.60 4x 76.10

2 – C –

2x 2.60

2x 5.28 2x 26.40 2x 12.00

4 –CF3

4x 8.00

4x 34.08 4x 90.00 4x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

∑ 250.16 642.88 1540.38 926.60


LL

LL

PVVP

−+

=2

'ε (10)

2

'

=

MPVε (11)

We get values of dielectric constant ε′ for [6FDA + BDAF] at 1 kHz

ε′ = (2x250.16 + 642.88) ÷ 642.88 - 250.16) = 2.92 by eq. (10)

ε′ = (1540.38 ÷ 926.60)2 = 2.77 by eq. (11)

LITERATURE Value : ε′ = 2.99 (at 100 kHz)*

EXPERIMENTAL Value : ε′ = 3.00 (at 1 kHz) * : Chapter 3, References # [80]

333

B-5. Fluoro-copoly(ether imide)s B-5.1. Estimation of dielectric constant of [6FDA + (75%) p-SED + (25%)

BPADE] fluoro-copoly(ether imide)

C C

C

C

CF3

O O

O

NNCO

CF3

Fluoro-copoly(ether imide): [ 6FDA +(75%) p-SED + (25%) BPADE ] (6F-CoPEI)

0.75

C

CH3

OO

CH3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.25

O



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4 4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

0.75 – SO2–

0.75x18.40

0.75x32.50 0.75x120.00 0.75x64.06

0.25 H3C– C –CH3

0.25x13.90 0.25x49.00 0.25x 61.70 0.25x42.00

∑ 248.835 606.065 1439.365 835.145 Now using Vora-Wang’s equations (13) and (14) respectively

)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)

We get values of dielectric constant ε′ for [6FDA + (75%) p-SED + (25%) BPADE] at 1 kHz

ε′ = (2x248.835 + 606.065) ÷ 606.065 - 248.835) = 3.09 by eq. (13)

ε′ = (1439.365 ÷ 835.1445)2 = 2.97 by eq. (14)


334


C C

C

C

CF3

O O

O

NNCO

CF3

Fluoro-copoly(ether imide): [ 6FDA +(50%) p-SED + (50%) BPADE ] (6F-CoPEI)

0.50

C

CH3

OO

CH3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.50

O



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4 4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

0.50 – SO2–

0.50x18.40

0.50x32.50 0.50x120.00 0.50x64.06

0.50 H3C– C –CH3

0.50x13.90 0.50x 49.0 0.50x 61.70 0.50x 42.0

∑ 247.71 610.19 1424.83 830.63


)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)


ε′ = (2x247.71 + 610.19) ÷ 610.19 - 247.71) = 3.05 by eq. (13)

ε′ = (1424.83 ÷ 830.63)2 = 2.94 by eq. (14)


335

B-5.3. Estimation of dielectric constant of 6FDA + (25%) p-SED + (75%) BPADE] fluoro-copoly(ether imide)

C C

C

C

CF3

O O

O

NNCO

CF3


0.25

C

CH3

OO

CH3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.75

O

Group Contribution of Molar Polarization

No. of Groups

GROUP PLL V PV M

2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4 4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

0.25 – SO2–

0.25x18.40

0.25x32.50 0.25x120.00 0.25x64.06

0.75 H3C– C –CH3

0.75x13.90 0.75x49.00 0.75x 61.70 0.75x42.00

∑ 246.585 614.315 1410.215 824.115


)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)


ε′ = (2x246.585 + 614.315) ÷ 614.315 - 246.585) = 3.01 by eq. (18)

ε′ = (1410.215 ÷ 824.115)2 = 2.93 by eq. (19)


336


C C

C

C

CF3

O O

O

NNCO

CF3

Fluoro-copoly(ether imide): [ 6FDA +(75%) p-SED + (25%) BDAF ] (6F-CoPEI)

0.75

C

CF3

OO

CF3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.25

O



2 C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4 4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

0.75 – SO2–

0.75x18.40

0.75x32.50 0.75x120.00 0.75x64.06

0.25 F3C– C –CF3

0.25x18.60 0.25x72.24 0.25x206.00 0.25x42.00

∑ 250.01 611.875 1475.54 862.15


)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)

We get values of dielectric constant ε′ for [6FDA + (75%) p-SED + (25%) BDAF] at 1 kHz

ε′ = (2x250.01 + 611.875) ÷ 611.875 - 250.01) = 3.07 by eq. (13)

ε′ = (1475.54 ÷ 862.15)2 = 2.93 by eq. (14)


337


C C

C

C

CF3

O O

O

NNCO

CF3

Fluoro-copoly(ether imide): [ 6FDA + (50%) p-SED + (50%) BDAF ] (6F-PEI)

0.50

C

CF3

OO

CF3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.50

O



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4 4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

0.50 – SO2–

0.50x18.40

0.50x32.50 0.50x120.00 0.50x 64.06

0.50 F3C– C –CF3

0.50x18.60 0.50x72.24 0.50x206.40 0.50x150.02.

∑ 250.06 621.81 1497.18 883.63


)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)


ε′ = (2x250.06 + 621.81) ÷ 621.81 - 250.06) = 3.02 by eq. (13)

ε′ = (1424.83 ÷ 830.63)2 = 2.87 by eq. (14)


338


C C

C

C

CF3

O O

O

NNCO

CF3

Fluoro-copoly(ether imide): [ 6FDA + (25%) p-SED + (75%) BDAF ] (6F-CoPEI)

0.25

C

CF3

OO

CF3

SO

OOC C

C

C

CF3

O O

O

NCO

CF3

N

0.75

O



2

C

O

NCO

2x 51.28

2x 108.50 2x 276.59 2x 145.10

4 4x 25.00

4x 65.50 4x 128.60 4x 76.10

1 – C –

1x 2.60

1x 5.28 1x 26.40 1x 12.00

2 –CF3

2x 8.00

2x 34.08 2x 90.00 2x 69.00

2 – O –

2x 5.20

2x 8.50 2x 30.00 2x 16.00

0.25 – SO2–

0.25x18.40

0.25x32.50 0.25x120.00 0.25x 64.06

0.75 F3C– C –CF3

0.75x18.60 0.75x72.24 0.75x206.40 0.75x150.02

∑ 250.11 631.745 1518.74 905.13


)()()2()2(2

'2211

2211

LLLL

LLLL

LLCOCO

COLLCOCO PVmPVn

VPmVPnPV

VP−+−

+++=

−+

=ε (13)

2

21

212

'

++

=

=

mMnMmPnP

MP VV

CO

VCOCOε (14)


ε′ = (2x250.11 + 631.745) ÷ 631.745 - 250.11) = 2.97 by eq. (13)

ε′ = (1518.74 ÷ 905.13)2 = 2.82 by eq. (14)


Documents

SYNTHESIS, FABRICATION, CHARACTERIZATION, …ii ROHIT KUMAR H. VORA Degree: Doctor of Philosophy (PhD), 1998-2003. Department: Chemistry PhD Thesis Title: Synthesis, Fabrication, Characterization,