Thermoplastic elastomers via controlled radical …Thermoplastic Elastomers via Controlled Radical Graft Polymerization PROEFSCHRIFT ter verkrijging van de graad van doctor aan de

Thermoplastic elastomers via controlled radical graftpolymerizationCitation for published version (APA):Tuzcu, G. (2012). Thermoplastic elastomers via controlled radical graft polymerization. Technische UniversiteitEindhoven. https://doi.org/10.6100/IR739789

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https://doi.org/10.6100/IR739789

https://doi.org/10.6100/IR739789

https://research.tue.nl/en/publications/thermoplastic-elastomers-via-controlled-radical-graft-polymerization(61692637-7226-44c1-897d-fe1345877ab2).html

Thermoplastic Elastomers via Controlled Radical

Graft Polymerization

PROEFSCHRIFT

ter verkrijging van de graad van doctor aan de TechnischeUniversiteit Eindhoven, op gezag van de rector magnificus,

prof.dr.ir. C.J. van Duijn, voor een commissie aangewezen doorhet College voor Promoties in het openbaar te verdedigen op

woensdag 31 oktober 2012 om 16.00 uur

door

Gozde Tuzcu

geboren te Izmit, Turkije

mailto:[email protected]





http://www.something.net

http://www.something.net

Dit proefschrift is goedgekeurd door de promotor:

prof.dr.ir. L. Klumperman

Copromotor:

dr.ir. J.G.P. Goossens

A catalogue record is available from the Eindhoven University of Technology Library.

ISBN: 978-90-386-3286-5

Copyright c© 2012 by Gozde Tuzcu

The work described in this thesis was performed at the Laboratories of Polymer Chem-

istry (SPC) and Polymer Technology (SKT) within the department of Chemistry and

Chemical Engineering, Eindhoven University of Technology, the Netherlands. This

work is part of the research program of the Dutch Polymer Institute (DPI), project

#649.

Printed by the Eindhoven University Press, The Netherlands.

Cover design by Gozde Tuzcu.

”Life is not the opposite of death.

Death is the opposite of birth.

Life is eternal.”

Anathema

To my family...

Contents

Glossary ix

1 Introduction 1

1.1 Rubbers and Thermoplastic Elastomers . . . . . . . . . . . . . . . . . . 2

1.1.1 Vulcanization and Thermoset Elastomers . . . . . . . . . . . . . 2

1.1.2 Thermoplastic Elastomers . . . . . . . . . . . . . . . . . . . . . . 3

1.1.2.1 Types and General Characteristics of Thermoplastic Elas-

tomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.1.2.2 Aspects of Industrial Production of TPEs . . . . . . . . 9

1.2 CRP in Macromolecular Architecture . . . . . . . . . . . . . . . . . . . . 11

1.2.1 Use of CRP methods in TPE synthesis . . . . . . . . . . . . . . . 13

Bibliography 19

2 Synthesis and End-group Functionalization of Thermoplastic Poly-

mers 23

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.2 Experimental Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.2.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.2.3 Synthesis of PS and P(SMI) with ω-amine Functionality . . . . . 29

2.2.3.1 ω-Bromide-functional PS . . . . . . . . . . . . . . . . . 29

2.2.3.2 ω-Amine-functional PS . . . . . . . . . . . . . . . . . . 30

2.2.3.3 α-Nitrile-functional PS . . . . . . . . . . . . . . . . . . 31

2.2.3.4 α-Amine-functional PS . . . . . . . . . . . . . . . . . . 31

2.2.3.5 ω-Bromide-functional P(SMI) . . . . . . . . . . . . . . 31

iii

CONTENTS

2.2.3.6 ω-Amine-functional P(SMI) . . . . . . . . . . . . . . . . 32

2.2.4 Synthesis of PS and P(SMI) with ω-thiol Functionality . . . . . . 32

2.2.4.1 ω-Dithioester-functional PS . . . . . . . . . . . . . . . . 32

2.2.4.2 ω-Thiol-functional PS . . . . . . . . . . . . . . . . . . . 32

2.2.4.3 ω-Dithioester-functional P(SMI) . . . . . . . . . . . . . 32

2.2.4.4 ω-Thiol-functional P(SMI) . . . . . . . . . . . . . . . . 33

2.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.3.1 ARGET ATRP of Styrene . . . . . . . . . . . . . . . . . . . . . . 33

2.3.2 Transformation of Bromide Moiety to Amine in PS . . . . . . . . 35

2.3.3 Transformation of Bromide Moiety to Thiol in PS . . . . . . . . 40

2.3.4 RAFT Polymerization of Styrene . . . . . . . . . . . . . . . . . . 42

2.3.5 Transformation of Nitrile Moiety into Amine in PS . . . . . . . . 45

2.3.6 Transformation of Dithioester Moiety into Thiol in PS . . . . . . 47

2.3.7 ω-Amine-functional P(SMI) . . . . . . . . . . . . . . . . . . . . . 50

2.3.8 ω-Thiol-functional P(SMI) . . . . . . . . . . . . . . . . . . . . . . 53

2.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Bibliography 59

3 Thermoplastic Elastomers via Amine-Anhydride Coupling 61

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62


3.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

3.2.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

3.2.3 Dehydration of Maleic Acid Pendant-functions on EPM . . . . . 65

3.2.4 Amine-anhydride Coupling of EPM and PS-NH2 . . . . . . . . . 65

3.2.5 Amine-anhydride Coupling of EPM and P(SMI)-NH2 . . . . . . 65

3.2.6 Dehydration of Amic Acid Function into Imide . . . . . . . . . . 65


3.3.1 Approaches for the Quantitative Analysis of Grafting Efficiency . 66

3.3.2 Effect of Molar Mass of Building Blocks . . . . . . . . . . . . . . 69

3.3.2.1 Molar Mass of the Grafting Chain . . . . . . . . . . . . 69

3.3.2.2 Molar Mass and Functionality of the Grafted Chain . . 71

3.3.3 Effect of the Composition of the Building Blocks . . . . . . . . . 72

iv

CONTENTS

3.3.4 Effect of Stoichiometry of Building Blocks and Reaction Concen-

tration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Bibliography 77

4 Thermoplastic Elastomers via Thiol-ene Coupling 79

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80


4.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

4.2.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

4.2.3 Model Reactions for Thiol-ene Coupling . . . . . . . . . . . . . . 82

4.2.4 Thiol-ene Coupling of Vinylic PB and PS-SH . . . . . . . . . . . 83

4.2.5 Thiol-ene Coupling of Vinylic PB and P(SMI) . . . . . . . . . . 83


4.3.1 Proof of Concept - Model Reactions . . . . . . . . . . . . . . . . 83

4.3.2 Radical Thiol-ene Coupling in Polymer-polymer Coupling . . . . 86

4.3.3 Effect of Molar Mass of Building Blocks . . . . . . . . . . . . . . 88

4.3.3.1 Molar Mass of the Grafting Chain . . . . . . . . . . . . 88

4.3.3.2 Molar Mass of the Grafted Chain . . . . . . . . . . . . 89

4.3.4 Effect of Stoichiometry of Building Blocks and Reaction Concen-

tration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

4.3.5 Composition of Building Blocks, Effects of Two-solvent System . 91

4.3.6 Effect of Reaction Temperature and Initiator Activity . . . . . . 95

4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Bibliography 99

5 Thermoplastic Elastomers via Nitroxide Mediated Graft Polymeriza-

tion 101

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102


5.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

5.2.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

5.2.3 Synthesis of Amine-functional NMP Initiator . . . . . . . . . . . 105

v

CONTENTS

5.2.3.1 Synthesis of 2-methyl-2-[N-tert-butyl-N-(1-diethoxyphosphoryl-

2,2-dimehtylpropyl)amino]-N-propionylsuccinimide (NPS

SG-1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

5.2.3.2 Synthesis of 2-methyl-2-[N-tert-butyl-N-(1-diethoxyphosphoryl-

2,2-dimethylpropyl)aminoxy]-N-aminoethylpropionamide

(NAP SG-1) . . . . . . . . . . . . . . . . . . . . . . . . 105

5.2.4 NMP of Styrene . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

5.2.5 Ex-situ Modification of ω-nitroxide Functionality . . . . . . . . . 106

5.2.6 Synthesis of NMP Macroinitiator . . . . . . . . . . . . . . . . . . 106

5.2.7 Graft Polymerization of Styrene from Macroinitiator . . . . . . . 106

5.2.8 In-situ Modification of ω-nitroxide Functionality . . . . . . . . . 107


5.3.1 Synthesis of Amine-functional NMP Initiator . . . . . . . . . . . 107

5.3.2 A pre-study: NMP of Styrene . . . . . . . . . . . . . . . . . . . . 109

5.3.3 In-situ and Ex-situ End-modification of ω-nitroxide-functional PS 112

5.3.4 Synthesis of NMP Macroinitiator . . . . . . . . . . . . . . . . . . 113

5.3.5 Graft Polymerization of Styrene from Macroinitiator and In-situ

Modification of the Nitroxide Functionality . . . . . . . . . . . . 115

5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

Bibliography 121

6 Structure-Property Relations of TPEs with Graft Topology 123

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124


6.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

6.2.2 Methods and Characterization Techniques . . . . . . . . . . . . . 126

6.2.2.1 TEM Measurements of the Samples . . . . . . . . . . . 126

6.2.2.2 Compression Molding of the TPE Samples . . . . . . . 126

6.2.2.3 DMTA Analysis of TPE Samples . . . . . . . . . . . . . 126

6.2.2.4 Tensile Tests of TPE Samples . . . . . . . . . . . . . . 126

6.2.2.5 Interpretation of Data . . . . . . . . . . . . . . . . . . . 127


6.3.1 Morphology of the Graft TPEs: A General Comparison . . . . . 127

vi

CONTENTS

6.3.2 Effect of Stoichiometry of the Components . . . . . . . . . . . . 129

6.3.2.1 Morphology . . . . . . . . . . . . . . . . . . . . . . . . . 129

6.3.2.2 Thermomechanical Properties . . . . . . . . . . . . . . 129

6.3.2.3 Tensile Properties . . . . . . . . . . . . . . . . . . . . . 132

6.3.3 Effect of Coupling Efficiency . . . . . . . . . . . . . . . . . . . . 132

6.3.3.1 Morphology . . . . . . . . . . . . . . . . . . . . . . . . . 132



6.3.4 Effect of the Molar Mass of the Components . . . . . . . . . . . 140

6.3.4.1 Morphology . . . . . . . . . . . . . . . . . . . . . . . . . 140



6.3.5 Effect of the Composition of the Building Blocks . . . . . . . . . 144

6.3.5.1 Thermomechanical and Tensile Properties . . . . . . . . 145

6.3.6 Effect of Topology . . . . . . . . . . . . . . . . . . . . . . . . . . 147

6.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

Bibliography 153

7 Outlook 155

Bibliography 159

Summary 161

Acknowledgements 165

Curriculum Vitae 169

vii

Glossary

1-PEBr (1-bromoethyl) benzene

∆Gmix Gibbs free energy of mixing

∆Hmix enthalpy of mixing

∆Smix entropy of mixing

σmax maximum stress

σR stress at break

σ50 stress at 50% elongation

σ100 stress at 100% elongation

ACHN 1,1’-Azobis(cyclohexanecarbonitrile)

AIBN azobisisobutyronitrile

AMVN 2,2’-Azobis(2.4-dimethyl valeroni-

trile)

ARGET activators regenerated by electron

transfer

ATR attenuated total reflectance

ATRP atom transfer radical polymerization

BHT 3,5-di-tert-butyl-4-hydroxytoluene

BMS BH3.S(CH3)2, borane dimethyl sul-

fide complex

CDB cumyl dithiobenzoate

CE coupling efficiency

CHCl3 chloroform

CIPDB 2-cyanoisoprop-2-yl dithiobenzoate

CRP controlled radical polymerization

CTA chain transfer agent

CuBr2 copper(II)bromide

D dispersity

DCC N-N’dicyclohexylcarbodiimide

DCM dichloromethane

DCU N,N’-dicyclohexylurea

DMF dimethyl formamide

DMTA dynamic mechanical thermal analysis

E′ storage modulus

εR strain at break

EBiB ethyl 2-bromo-2-methylpropanoate

EPM maleated poly(ethylene-co-

propylene) rubber

EPDM poly(ethylene-co-propylene-co-

diene) rubber

EVA poly(ethylene-co-vinyl acetate)

FTIR fourier transform infrared spec-

troscopy

GC gas chromatography

GPEC gradient polymer elution chromatog-

raphy

HCl hydrochloric acid

LDPE low density polyethylene

LiAlH4 lithium aluminum hydride

MALDI-TOF-MS matrix assisted laser des-

orption/ionization time-of-flight

mass spectrometer

MAMA SG-1 2-((tert-butyl(1-(diethoxyphosphoryl)-

2,2-dimethylpropyl)amino)oxy)-2-

methylpropanoic acid

Me6TREN tris[2-(dimethylamino)ethyl]amine

MgSO4 magnesium sulfate

M c molar mass between the crosslink

points

M e entanglement molar mass

ix

GLOSSARY

M n number average molar mass

M p peak molar mass

NPS SG-1 2,5-dioxopyrrolidin-1-yl-2-((tert-

butyl(1-(diethoxyphosphoryl)-

2,2-dimethylpropyl)amino)oxy)-2-

methylpropanoate

NAP SG-1 diethyl (1-(((1-((2-aminoethyl)amino)-

2-methyl-1-oxopropan-2-yl)oxy)(tert-

butyl)amino)-2,2-dimethylpropyl)

phosphonate

N2H4.H2O hydrazine monohydrate

NaN3 sodium azide

NaOH sodium hydroxide

NHS N-hydroxysuccinimide

NMP nitroxide mediated polymerization

NMR nuclear magnetic resonance

NR natural rubber

PB 1,2-polybutadiene

P(Bu)3 tributylphosphine

P(Ph)3 triphenylphosphine

PS polystyrene

P(SMA) poly(styrene-alt-maleic anhydride)

P(SMI) poly(styrene-alt-N-phenyl maleimide)

PVC poly(vinylchloride)

RAFT reversible addition fragmentation

chain transfer

RI refractive index

SEBS poly(styrene-b-ethylene/butylene-b-

styrene)

SEC size exclusion chromatography

SN2 bimolecular nucleophilic substitution

TAI trichloroacetyl isocyanate

TC thermoplastic component

TEM transmission electron microscopy

THF tetrahydrofuran

Tg glass transition temperature

Tm melting temperature

TPE thermoplastic elastomer

UV ultraviolet

x

1

Introduction

Abstract

Thermoplastic elastomers (TPEs) are the successors of conventional thermoset rub-

bers. While bringing cheaper solutions for the production process, they introduce new

tunable properties by utilizing new inventions in macromolecular engineering. Despite

the polymerization step, which is more sophisticated and expensive, the overall pro-

duction process is more profitable than conventional thermoset elastomer production

due to the excluded curing step. Now, controlled/living radical polymerization (CRP)

techniques provide simpler and robust polymerization conditions while bringing the

possibility of controlling the architecture of the macromolecules and is expected to be

a robust tool for the polymer industry. In this PhD study, TPEs with graft copolymer

topology were studied by utilizing CRP techniques in different synthetic approaches.

1

1 Introduction

1.1 Rubbers and Thermoplastic Elastomers

The words ‘elastomer’ and ‘rubber’ are generally used interchangeably. The word

‘elastomer’ is derived from elastic polymer and is a general term used for every kind

of polymer, which shows elastic behavior. However, the word ‘rubber’ is preferably

used for vulcanizates that are chemically crosslinked. An elastomer backbone can be

saturated such as ethylene propylene rubber (EPM), unsaturated such as natural rubber

(NR), or have pendant functionalities such as neoprene. An elastomer without chemical

or physical crosslinks is not sufficiently resistant against high shear or high temperature

applications. Desired rubbery behavior with a high temperature and shear resistance

can be achieved by forming a network structure within the elastomeric chains. Methods

that have been used for rubber and thermoplastic elastomer production and general

characteristic of different types of elastomers will be discussed in the following sections.

1.1.1 Vulcanization and Thermoset Elastomers

Natural rubber is a temperature and oxygen sensitive material due to fact that it

contains a large number of unsaturated bonds and has a low T g. Vulcanization by

molecular sulfur is the first technique invented for producing a durable elastomer with

good mechanical properties. Vulcanization is a general name for the chemical reactions

used for forming a 3-D network structure within the elastomer chains. There are sev-

eral vulcanization methods being used depending on the type of the elastomer to be

crosslinked. In industry, mainly two different vulcanization techniques are used: sul-

fur vulcanization and peroxide vulcanization. Sulfur vulcanization is the first method

invented by Charles Goodyear in 1844, and it is used for curing elastomers with unsat-

urated bonds. Peroxide vulcanization became more interesting after the introduction

of new synthetic elastomers with a saturated main chain. This interest was due to

the simpler chemistry involved in peroxide vulcanization. The peroxide vulcanization

process results in the formation of only covalent carbon-carbon bonds between the elas-

tomer chains, whereas in sulfur vulcanization, sulfide linkages form as well as covalent

carbon-carbon bonds. In this respect, sulfur vulcanization formulation would be more

complicated than peroxide formulation. However, the peroxide vulcanization reaction

has its own disadvantages, such as oxygen sensitivity. Eventually, both techniques have

2


their own specifications and are widely used in the rubber industry for the production

of thermoset elastomers with varying properties.

In vulcanization processes, a 3-D network structure is established. This covalent

crosslinking prevents the material to flow at elevated temperatures. This feature leads

the crosslinked rubbers to be used in high shear applications such as tires. However,

crosslinking prevents reprocessing and recycling, as well. There are some techniques

used [1] for recycling of the crosslinking rubber such as pulverizing under high shear

stress and devulcanizing at high temperatures in an extruder. The elastic constant of

S-S bonds is much lower than that of C-C bonds, therefore the pulverization process

under high shear potentially leads to selective devulcanization. There are chemical

techniques that selectively cleave the sulfur linkages, such as reacting the swollen rub-

ber with alkali metals [2]. Devulcanization processes need to be improved to provide

simpler and cheaper solutions for rubber recovery, since the waste rubber as landfills is

overwhelmingly increased and this way of processing the waste rubber is not economical

and environmentally friendly [3]. However, devulcanization of scrap rubber is an extra

step in the production of recycled rubber, which increases the energy consumption and

almost every technique results in partially degraded rubber [3]. Thermoset elastomer

production essentially returns to the producer costly with additional vulcanization step

and a devulcanization step for the reclaim of the rubber, which is not efficient or eco-

nomical. Thermal stability of the thermoset rubber brings the limitations in reclaiming

and reprocessing. Thermoplastic elastomers could be the solution for this contradiction

between the high thermal stability and efficient reprocessibility. TPEs may become the

successors of crosslinked rubbers if thermal stability gets improved with retention of

reprocessing efficiency.

1.1.2 Thermoplastic Elastomers

Following the significant development in applications of polymer chemistry during

World War II, it was possible to produce polymers with desired composition and

constitution. Thermoplastic elastomers have been invented and commercial produc-

tion has been started in the 1950s, with the first patent by DuPont on thermoplas-

tic polyurethanes [4]. Before TPEs were developed, only crosslinked rubbers and

plasticized PVC were available in the market as a flexible/rubbery material. While

crosslinked rubbers show so-called rubbery behavior, they have disadvantages in terms

3

1 Introduction

of compounding with fillers, stabilizers and curing agents and in terms of reprocessi-

bility, plasticized PVC is a thermoplastic material, which can be reprocessed and com-

pounded [5]. Low density polyethylene (LDPE) and ethylene-vinyl acetate copolymer

(EVA) are other examples of thermoplastic polymers that can be flexible. However, the

ultimate property of these materials are not rubbery due to absence chemical/physical

network formation among the chains. The key property of a thermoplastic elastomer is

a consistent rubbery behavior over a temperature range, which EVA or PVC does not

have [6],[7]. This behavior could only be achieved by vulcanization of the rubbers. The

contradiction of achieving a rubbery behavior and reprocessing between the crosslinked

rubbers and plasticized PVC-like materials were to be resolved by thermoplastic elas-

tomers.

1.1.2.1 Types and General Characteristics of Thermoplastic Elastomers

Commercially available TPEs are also either block copolymers with incompatible

segments, or elastomer/hard thermoplastic polymer blends. Blends generally exhibit

macrophase separation (domain size in µm scale), while block copolymers have a mi-

crophase separation, which is also called segregation (domain size in nm scale). An

illustration of phase separation in TPEs is shown in Figure 1.1.

Block copolymers can be classified into two main types, which are copolymers with

a crystalline hard phase and those with an amorphous hard phase. The figure illustrates

the TPE morphology with an amorphous hard phase. TPEs with an amorphous hard

phase have two distinct T gs, separately for the soft and the hard phase, while TPEs

with a crystalline hard phase have a T g for the soft phase and a Tm for the crystalline

phase. An example of a typical modulus-temperature curve for a styrenic TPE is

shown in Figure 1.2, which has similar thermomechanical behavior as semi-crystalline

block TPEs. Modulus-temperature curves are obtained by dynamic mechanical thermal

analysis (DMTA) measurements. This technique provides information about the T g

of the phases, the hardness of the material, the temperature window where rubbery

behavior is observed, and suitable temperature values for the melt processing.

The T g or Tm of the hard phase is generally far above ambient temperature to

be able to give sufficient stiffness to TPE in a wide service temperature range and

related to the flow temperature, T flow of the material, which is the temperature for

the processing (point D in Figure 1.2). The T g value of the elastomer phase indicates

4


Figure 1.1: Illustration of the phase separation in TPEs - Blue areas are denotedas the dispersed hard phase, and black lines are the matrix elastomer phase

mo

du

lus

(MP

a)

temperature ( C)°temperature ( C)°

1000

1

100

10

-50 0 50 100 150

A

B

C

D

Figure 1.2: Typical modulus-temperature curve for styrenic TPEs - point A isthe T g of elastomer phase, point B is the Tflex, point C is the T g of the hard phase, andpoint D is Tflow

5

1 Introduction

the lowest temperature of rubbery behavior and is closely related to the T flex. T flex is

the temperature where rubbery behavior starts to be observed, which is the minimum

service temperature (point B in Figure 1.2). T g and/or Tm values are denoted as the

temperature values at the peak points of loss modulus-temperature curves and T flex

is denoted as the intercept point of the tangents of the glass transition and rubbery

plateau in storage modulus-temperature curve [8]. The temperature region until the

T g of the hard phase is called rubbery plateau, where the material is expected to have

a consistent, temperature-independent modulus. The modulus of the rubber plateau

determines the hardness of the material. In thermoset elastomers, this plateau contin-

ues until the degradation starts at very high temperatures, in TPEs, the rubber plateau

continues until the T g of the hard phase. T flow, which is the temperature at which

the material starts to flow, is the minimum temperature for melt processing. T flow in

DMTA analysis is the point where the storage modulus drops below 1 MPa, where the

material has no mechanical strength anymore. The slope of the curve at T g or Tm

indicates the dispersity of the chain length of the segments, which is reported both for

block copolymers with a crystallizable segment [8], and those with totally amorphous

segments [9]. A large slope value is indicative of a low dispersity of the chains constitut-

ing the phases. This parameter determines the consistency/temperature-dependence

of the rubbery plateau. TPEs with well-defined topology have steeper curves at the

phase-change points, which results in more consistent modulus at the rubber plateau,

and more well-defined T flex and T flow values.

An illustrative comparison of typical modulus-temperature curves of different poly-

meric materials is shown in Figure 1.3, which shows the main differences of thermo-

mechanical properties between a thermoplastic polymer, an elastomer, a thermoset

elastomer and a thermoplastic elastomer.

Below its T g, every material is in the glassy state and shows a high modulus.

Every polymer is hard and mostly brittle below its T g. Fully amorphous polymers,

which show no phase separation, have one T g, above this temperature they start to

flow (illustration (a) in Figure 1.3). An elastomer has similar behavior, however due

to the high entanglement density, it creeps with a very low modulus (illustration (b)).

Thermoset polymers, which have a network structure, have also only one T g, however

they do not flow above their T g, because the crosslinks prevent significant movement of

chains relative to each other (illustration (d)). Instead of flowing, the rubbery behavior

6


E’

(MP

a)

T ( C)°T ( C)°

( a )

( d )( c )

( b )

E’

(MP

a)

E’

(MP

a)

E’

(MP

a)

T ( C)°T ( C)°T ( C)°T ( C)°

T ( C)°T ( C)°

Figure 1.3: Illustrations of typical modulus-temperature curves of differentpolymeric materials - (a) thermoplastic polymer, (b) neat elastomer, (c) thermoplasticelastomer, (d) thermoset elastomer

remains until the material starts to degrade. Thermoplastic elastomers, as described

above in detail, shows a combined behavior of a thermoplastic polymer and an elastomer

(illustration (c)).

Additional properties such as elastic modulus, yield strength, and elongation at

break are distinguishing features of an elastic material. These features are investigated

by stress-strain curves obtained by tensile strength tests. A comparison of stress-strain

curves of polymeric materials with different mechanical properties is shown in Figure

1.4. A very hard and brittle material exhibits a behavior similar to curve A that has no

yield stress. The material breaks before it is exposed to plastic deformation. A material,

which is hard but not as brittle as the example of curve A, exhibits a yield point, but

breaks immediately due to insufficient entanglements, which is illustrated by the curve

B. If a thermoplastic material has sufficient entanglements, it shows a strain softening

after the yield point, where the material creeps. Strain softening continues up to the

point where the chains are aligned, possible local crystallization and entanglements

results in strain hardening. This behavior of a hard and tough material is illustrated

by the curve C. Neat elastomers have a tensile behavior similar to curve E, which is

7

1 Introduction

a very low yield stress, high elongation at break with a very low modulus. This is

actually the flow behavior of a highly viscous liquid. Thermoplastic elastomers have a

tensile behavior similar to curve D. Higher yield stress, due to the hard segment, but

no strain softening if there is no creep in the hard phase. The build-up in stress is due

to the physical crosslinks among the elastomer chains. Crosslinked rubber has similar

behavior as thermoplastic elastomers under tensile stress. However, crosslinked rubbers

show almost no yield stress, since they possess a perfect 3-D network structure, plastic

deformation is virtually absent. The elastic modulus of the crosslinked rubber depends

on the crosslinking density.

A B

C

D

E

stre

ss

strain

Figure 1.4: Typical stress-strain curves for different polymers - A, hard andbrittle; B, hard and strong; C, hard and tough; D, soft and tough; E, soft and weak

Elastic modulus is defined as the slope of the stress-strain curve in the elastic region.

Elastic modulus (stiffness) of thermoplastic elastomers with block topology depends

on the chain length of the soft block and the hard block(s). This feature eventually

defines the volume fractions of the hard phase and the soft phase. The chain length

of the segments determines the number of entanglements per chain as well, which is

another parameter determining the tensile properties. Furthermore, molar mass of

the elastomer segment between the crosslinking points (M c) has a direct relationship

with the stiffness of the corresponding material. This relationship is described by the

8


Equation 1.1 [10]:

f = (RTρ/Mc)(λ− 1/λ2) (1.1)

where f is the tensile stress; ρ is the density of the polymer; R is the gas constant; T

is the absolute temperature; M c is the molar mass between crosslinks; λ is the extension

ratio. A tri-block TPE has an M c value the same as the molar mass of the elastomer

segment. However, tensile behavior of a tri-block TPE deviates from the estimated

behavior due to neglecting the effects of hard phase as a filler and the entanglements

in the elastomeric phase [10]. This filler effect, especially in high volume percentages of

the hard segment results in a yield point in stress-strain curves with a strain softening,

where the hard segment creeps under stress.

1.1.2.2 Aspects of Industrial Production of TPEs

Commercially available TPEs consist of 6 different types, which can be classified into

two main groups of block copolymers with incompatible segments and elastomer/hard

thermoplastic polymer blends. A table for the classification of TPE materials is shown

in table 1.1.

Table 1.1: Types of commercial TPE products

TPEsType Class Production

methodStructure

Copolymers

TPE-S* anionic poly-merization

di-/tri-blockcopolymer

TPE-U polyaddition multi-blockcopolymer

TPE-E polycondensation multi-blockcopolymer

TPE-A polycondensation multi-blockcopolymer

BlendsTPE-O metal catalysis homo-

/copolymerblend

TPE-V metal catalysis homo-/copolymerblend

+ dynamic vul-canization

crosslinked

*TPE-S: styrenic TPEs, TPE-U: thermoplastic polyurethanes,TPE-E: thermoplastic polyesters, TPE-A: thermoplastic polyamidesTPE-O: thermoplastic polyolefins, TPE-V: thermoplastic vulcanizates

In industry, production techniques and formulations for TPE blends are greatly

9

1 Introduction

patented. The materials are based on a wide variety of thermoplastic polymers and

elastomers, which are obtained by simple blending, reactive blending or dynamic vul-

canization. Blending may be followed by a curing process resulting in a partially

crosslinked product, which is still reprocessible. Blending provides improvement of

the properties of the polymers and synthesis of new materials from existing polymers.

Blends have a wide variety of different types of polymers and elastomers. Thermoplastic

polyolefins (TPE-O) include the majority of the commercial TPE blends. Polyolefins

are synthesized via transition metal catalysis. The constitution of the polymers is de-

termined by the molecular structure of the metal complex used, which leads to partial

crystallization of the segments. TPE-Os consist of a semi-crystalline polyolefin (such as

PP or PE) and a polyolefin rubber (such as EPM or EPDM), and crystalline parts of the

segments phase separate, forming physical crosslinks that leads to a overall thermoplas-

tic elastomer characteristics. Miscibility of the phases enhances the co-crystallization

of the components [11], which plays a role in the morphology and properties of the

resultant blend. In industry, blends are partially cured for better durability.

Thermoplastic vulcanizates (TPE-V), which is a TPE blend dynamically vulcan-

ized during the compounding step. The resultant material is a crosslinked rubber

dispersed in a thermoplastic matrix. Vulcanization is generally done due to the low

tensile strength and oil resistance of the elastomer phase [12]. The classes of TPE

blends have no strict distinction. While there are simple blends of elastomers and ther-

moplastics, there are blends composed of copolymers, which used singularly as a TPE,

with thermoplastics and elastomers, to enhance the compatibility of the elastomer and

thermoplastic phases [13], or altering the morphology and properties of the TPE block

copolymer [14].

The other four types of TPEs are block copolymers exhibiting phase separation.

In industry, TPEs with block copolymer topology are being produced either via step-

growth polymerization (thermoplastic polyurethanes (TPE-U), polyesters (TPE-E) and

polyamides (TPE-A)) or anionic polymerization (styrenic TPEs, TPE-S).

In step-growth polymerization, segmented block copolymers are formed where the

hard segment is crystallisable and provides the driving force for the phase separation

[15]. The constitution of the segments are well-defined, however the D of the resultant

polymer is 2.0, which is typical in step-growth polymerization. Additionally, due to the

nature of step-growth polymerization, high molar masses can only be reached at high

10

1.2 CRP in Macromolecular Architecture

conversions. Therefore, the synthesis of TPEs are done in two steps, where first the α,ω-

di-functional oligomers are synthesized as a precursor of the blocks and block copolymer

is synthesized by the polycondensation of the oligomers [16]. This two-step process leads

to longer segments which would exhibit explicit crystallization. Production of TPEs via

step-growth polymerization is generally done in bulk, which needs high temperatures to

maintain the homogeneity of the reaction. These two requirements induce side reactions

throughout the polymerization process and lead to crosslinking/degradation [17].

Anionic polymerization is a living polymerization process. Polymers synthesized

via anionic polymerization have a D close to 1.0. The polymerization proceeds with

no termination until all the monomer is consumed. This feature provides the ability to

tune the properties of the material precisely by tuning the molar mass. The resultant

polymer can be further end-functionalized and copolymers with different topologies can

be achieved with various coupling techniques [18]. Disadvantage of such a technique

is the fact that water, oxygen and CO2 should be totally excluded from the reaction

environment. Trace amounts of those impurities lead to termination. This weakness of

anionic polymerization limits the industrial applications that requires robustness.


Controlled radical polymerization (CRP) is the most recent development for synthe-

sizing well defined polymers with low D values and high degrees of end-functionality.

Before the CRP methods were invented, the only living polymerization techniques were

ionic polymerizations (living cationic and anionic polymerization). Cationic polymer-

ization was very limited in terms of industrial application due to the hard control and

complexity of the polymerization reaction and very low temperatures needed for ob-

taining polymers with low dispersity [19]. Anionic polymerization is relatively more in-

dustrially applicable, since the reaction conditions are more convenient and controllable

[20] however both polymerization techniques suffer from the high sensitivity towards

water, oxygen and the type of solvent used, which makes the technique weak in terms of

industrial applications. Polycondensation or radical polymerization were widely used in

industrial applications in spite of high dispersities of the resultant polymers. By the in-

troduction of CRP techniques, it became possible to produce well-defined polymers via

fairly robust reaction conditions. There have been different CRP techniques developed

11

1 Introduction

in last decades, which can be divided into three main groups in terms of mechanism,

i.e. atom transfer radical polymerization (ATRP), reversible addition-fragmentation

chain-transfer polymerization (RAFT polymerization) and nitroxide-mediated radical

polymerization (NMP). The mechanism of these reactions will be introduced and dis-

cussed in detail in further chapters.

Since the 1960’s, polymer chemists have been searching for a polymerization tech-

nique that is living/pseudo-living and robust. In 1995, the groups of Matyjaszewski

and Sawamoto, independently reported ATRP, which was the most robust pseudo-

living polymerization reported to that date [21]. This discovery was a major step for

the industrial world as well as the scientific world, which enables the radical polymer-

ization to be controlled and tailored. ATRP works on the basis of a halogen atom

transfer between a growing chain and a metal complex, which makes the growing chain

switch between dormant and active mode, providing uniform growth of the chains.

Eventually, polymers with very low dispersity and high halogen end-functionality are

obtained. There are different ATRP methods serving different options for designing

suitable formulations for a specific application. For instance, reverse ATRP with active

catalysts is suitable for reactions which requires a low reaction temperature such as

emulsion polymerization [22]. Activators regenerated by electron transfer (ARGET)

ATRP serves an easy reaction set-up and low concentrations of metal halide, next to

the possibility of polymerization in presence of air with monomers bearing functions

that are intrinsic reducing agents [23].

RAFT polymerization was discovered as a controlled radical polymerization tech-

nique in 1998. RAFT polymerization can be used with a wide variety of monomers and

reaction conditions, resulting in very low dispersities [24]. RAFT polymerization mech-

anism is based on a conventional radical polymerization, in which the propagation was

controlled by chain transfer agents (CTA). Thiocarbonylthio compounds are generally

used as a CTA, and free radical initiators are used as initiators. Polymers synthe-

sized via RAFT polymerization have high thiocarbonyl thio end-functionality. There

are different types of CTA classified according to the Z substituent of the molecule,

e.g. dithiobenzoates, dithiocarbamates and trithiocarbonates. Each type of CTA has

different chain transfer rates that allow one to adjust the polymerization conditions

according to the reaction temperature, monomer and solvent to be selected [25]. The

rate of the polymerization is also tuned by using different R groups, which play a role in

12


determining the chain transfer coefficient relative to its stability in the form of a radical

[26]. In this respect, RAFT polymerization is a very versatile CRP technique, which

enables to have a reaction design according to the desired conditions and performance.

NMP has the simplest mechanism among all CRP methods. An alkoxyamine is

used both as a thermal initiator and as ‘capping’ agent. The ‘living’ nature of NMP

reactions is based on ‘persistent radical effect’ concept first proposed by Fischer [27],

on which ATRP is based, as well. The substituents on the alkoxyamine determine

the stability of the nitroxide radical, end-capping the growing polymer chain, and the

alkyl radical, initiating the polymerization, both of which are formed by the homolytic

dissociation of the alkoxyamine.

All three CRP methods performed in this thesis will be introduced and discussed

in detail in the relevant chapters.

Macromolecular architecture and tailoring has found new possibilities by the in-

troduction of CRP methods. Different CRP methods generate different chain-end

functionalities, and with various chemical reactions, it is possible to obtain various

chain-end functionalities that can be used for further polymer-polymer coupling re-

actions, switching polymerization methods for chain extension reactions to synthesize

novel copolymers with various topologies. The combination of different CRP methods

within each other and with robust and efficient chemical reactions allows the polymer

chemist to design almost any macromolecule imaginable. In this respect, one step fur-

ther is made in tailoring macromolecules to answer the needs of developing polymer

technology. However, there is still some way to go for an efficient and sustainable indus-

trial production. In this respect, nature is an excellent model for robust polymerization

techniques that provide monodisperse polymers with perfectly designed architectures.

The very best example of this concept is protein synthesis. Exploring nature’s way of

building macromolecules in an efficient and sustainable manner is the ultimate point of

polymer science. The gap between molecular biology and polymer chemistry is the con-

ditional challenge to overcome the limitation of mimicking/realizing nature in polymer

industry.

1.2.1 Use of CRP methods in TPE synthesis

In academia, many different techniques have been and are still being developed for

the synthesis of thermoplastic elastomers. Synthetic studies associated with TPEs

13

1 Introduction

are based on biodegradable blends or copolymers [28], [29]; copolymers with various

topologies such as star [30], graft [31],[32]; block copolymers synthesized with vari-

ous techniques such as RAFT emulsion polymerization [33]. Multi-block copolymers

produced via polyaddition are investigated in terms of biodegradability in recent years

[34]. Many experimental and theoretical studies are done for the structure-morphology-

property relations of TPEs with various topologies, such as modeling phase separation

behavior of TPEs with non-linear molecular structure, which showed that these non-

linear topologies lead to a better stabilization of spherical and cylindrical phases at high

volume fractions of the hard phase [35]. The mechanical properties of the TPE basi-

cally depend on the strength of the interaction between the two phases and the intrinsic

properties of each phase. The elastomeric phase is expected to have a large elastic de-

formation, while the thermoplastic phase is expected to be sufficiently hard to support

elastic deformation without creep. These parameters are dependent on macromolecular

topology as well as the composition of the segments. Composition of the segments is

one of the key parameters determining the elastic modulus and the temperature win-

dow for the rubbery behavior, due to the fact that it determines the T g and the Tm of

the phases. On the other hand, the topology of the copolymer is the main parameter

determining the properties of the interaction between the soft and the hard phase. A

TPE blend has only physical interaction between the phases, namely entanglements

and van der Waals interactions. Tri-block styrenic TPEs have covalent bonds between

the segments, which is the main reason for its superior properties compared to a blend.

Tri-block TPEs are currently synthesized by anionic polymerization. One of the main

reasons for this preference is the lack of a technique to polymerize olefins and thermo-

plastics in one pot. Polymerization of olefins is not possible via conventional radical

methods, due to poor control of the constitution, which leads to uncontrolled branch-

ing. The only way of using CRP methods on TPE synthesis is to use a pre-synthesized

elastomer and either modify it to a macroinitiator and polymerize the thermoplastic

segment from it, or make copolymers with block or graft topology via polymer-polymer

coupling with a high end-functional thermoplastic polymer. The ultimate properties

are ideally expected to be obtained by tri-/multi-block topology, in which the elastomer

segment is covalently bonded to two thermoplastic segment from both chain-ends. Al-

though the tri-block topology is the best structure for the best properties, due to the

large chain lengths, the melt viscosity of the block copolymer is much higher than the

14


intrinsic viscosities of the homopolymers constituting the building blocks [10]. This

leads to limitations in the flow process due to high entanglement density per chain and

high order-disorder transition temperatures. The research on TPEs therefore shifted

to graft and star topologies, in which CRP techniques and click reactions are widely

used. While TPEs with star topology can be considered as a bundle of block copoly-

mers, TPEs with graft topology slightly differ from TPEs with block topology. In the

graft topology, hard segments are chemically bonded to the elastomeric main chain as

pendant chains. The graft topology does not significantly change the hydrodynamic

volume of the main chain, which is expected to have no significant effect on viscosity, as

well. In this manner, graft topology could be an alternative to overcome the processing

limitations of TPEs. In Figure 1.5 two cartoons illustrate the TPEs with block and

graft topologies.

HP

SP (M )c

HP

SP

(M )cDE

Figure 1.5: Illustrative comparison of a block and a graft topology - HP: hardphase, SP: soft phase, M c: molar mass between crosslinking points, DE: dangling end

In graft topology, the parameters determining the structure-property relations are

different than those in block-topology. First of all, the M c value changes in conjunction

with the grafting density. Secondly, graft topology results in dangling ends at both sides

of the elastomer main chain. The chain length of the dangling ends is another parameter

that is also related to the grafting density. Thirdly, there is a correlation between

the chain length and the grafting density in terms of weight fraction of the grafted

chains. The weight fraction of the hard segment should not exceed a certain value,

which depends on the interaction parameters of the components, otherwise it leads

to phase inversion. This brings an inverse correlation between the grafting density

15

1 Introduction

and the length of the grafted chain for a certain weight ratios of the components.

The key element in synthesizing TPEs with graft topology is the degree of control

over the resultant structure, namely narrow distribution of the chain lengths and a

minimum fraction of free non-grafted chains. In polymer chemistry, three different

approaches are used for the synthesis of a copolymer with graft topology involving

CRP techniques. First approach is ‘grafting through’, in which a mixture of monomers

and macromonomers are copolymerized in one pot. Monomers constitute the main

chain and the macromonomers constitute the grafting chains. Second approach is

called ‘grafting onto’, in which the main chain with pendant functions and grafting

chains with end-functionalities are synthesized separately and conjugated via coupling

reactions. The third approach is called ‘grafting from’, in which the main chain polymer

is employed as a macroinitiator and the monomer is polymerized from the initiating

pendant functions, constituting the grafting chains. All three grafting approaches are

illustrated in Figure 1.6

( a )

( c )

( b )

Figure 1.6: Grafting reactions - (a) grafting onto, (b) grafting from, (c) graftingthrough

In this thesis, ‘grafting onto’ and ‘grafting from’ approaches are investigated. ‘Graft-

ing through’ is not an option, since copolymerization of olefins with thermoplastic

macromonomers via CRP techniques or conventional free radical methods is not cur-

rently possible, as explained above. In the ‘grafting onto’ approach, amine-anhydride

16


and radical thiol-ene coupling reactions are investigated, to achieve desired thiol and

amine end-functionalities, RAFT polymerization and ARGET ATRP are employed.

ATRP and RAFT polymerization will be introduced and discussed in detail in Chapter

2. The ‘Grafting onto’ approaches by amine-anhydride coupling and radical thiol-ene

coupling are introduced and discussed in Chapter 3 and 4, respectively. In the ‘grafting

from’ approach, NMP is investigated, since this technique has a simple formulation.

This technique will be introduced in Chapter 5, which relates to the synthesis of TPEs

with nitroxide mediated graft polymerization. All synthesized TPEs with graft topol-

ogy are compared in terms of structure-morphology-property relations in Chapter 6.

Outlook and recommendations are given in Chapter 7.

17

1 Introduction

18

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22

2

Synthesis and End-group

Functionalization of

Thermoplastic Polymers

Abstract

Performance of a macromolecular architecture based on polymer-polymer coupling

is strongly dependent on well-defined building blocks. CRP techniques make it possi-

ble to synthesize a wide range of different types of polymers with low dispersity (D)

and desired chain-end functionality with high yields in a robust way. In this chapter,

the synthesis of two different high T g thermoplastic polymer, polystyrene (PS) and

poly(styrene-alt-N-phenyl maleimide)(P(SMI)) have been described with two different

desired chain end-functionalities, which are thiol and amine moieties. These high T g

polymers have been used further for polymer-polymer coupling studies, which will be

reported in detail in following chapters.

23

2 Synthesis and End-group Functionalization of Thermoplastic Polymers

2.1 Introduction

The most straight-forward way to obtain well-defined amorphous high T g polymers

with high ω- or α- functionality starts with a suitable living radical polymerization tech-

nique. The polymer chain is terminated or initiated by a suitable functionality that, if

necessary, can be converted into the desired end-group. One of the controlled polymer-

ization methods that has been performed in the present study is ARGET ATRP. ATRP

in general provides a ω-halide functionality, which is considered as a good leaving group

for nucleophilic substitution or elimination reactions. Additionally, PS synthesized by

ARGET ATRP has a high chain-end functionality (around 90%), and dispersity of 1.2

for conversions of 40% or higher [1]. All these features make ARGET ATRP products

excellent building blocks for further polymer-polymer coupling reactions.

One of the motivations to choose ARGET ATRP is the fact that the amount of

copper used is much less than the amount used in a conventional ATRP procedure,

which is more environment-friendly and makes the follow-up of the polymerization and

the work-up easier. Secondly, the presence of a reducing agent in excess amount helps

to make the reaction less sensitive to oxygen, which makes the reaction more robust

while resulting in low dispersity and high functionalities.The third motivation for using

ARGET ATRP is that ascorbic acid, which is used as a reducing agent, has a limited

solubility in anisole. This leads to a reduction in propagation rate relative to a solvent

in which the reducing agent would be completely soluble. [2].

The other polymerization technique performed in the current study is RAFT poly-

merization. The motivation for using the RAFT polymerization technique was to be

able to obtain higher ω-thiol functionality, which was only 60% via ARGET ATRP

followed by S -alkylation. RAFT polymerizations performed with CIPDB results in

ω-dithiobenzoate functionality and α-nitrile functionality, which could be transformed

into a thiol via aminolysis and an amine via reduction, respectively. Additionally,

RAFT polymerization is compatible with the maleic anhydride monomer unlike ATRP.

Copolymerization of maleic anhydride with styrene will result in a thermoplastic poly-

mer with a higher T g next to the improved surface adhesion properties thanks to the

anhydride functionalities.

Motivations for postpolymerization reactions described in the literature are gener-

ally polymer-polymer coupling reactions or reinitiation by various types of polymer-

24

2.1 Introduction

izations. Polymer-polymer coupling studies are nowadays often based on robust click

reactions such as Huisgen azide-alkyne 1,3-cycloaddition [3]. The combination of dif-

ferent polymerization methods is studied to utilize the advantages of each technique

such as the synthesis of block copolymers where both blocks require different poly-

merization methods [4] or the synthesis of block or multiarm star copolymers with a

heterogeneous di- or tri- functional CRP initiator without the disadvantage of low yield

end-functionality of the macroinitiator [5]. Both RAFT and ATRP techniques are the

basic tools used intensively for the synthesis of complex macromolecular architectures.

In this study, as indicated above, the CRP methods are used to obtain highly ω- or

α-functional polymers, which will be used as building blocks for coupling reactions on

the way to the synhtesis of TPEs with graft topology. The post-polymerization reac-

tions done on ω-bromide-functional and ω-dithioester-functional polymers were chosen

according to the desired amine and thiol functionality. The minimum number of steps

and maximum conversion yields were sought and the techniques were compared in terms

of these features.

Among all approaches for the synthesis of ω-amine-functional polymers, the first

approach (route 1) was Gabriel synthesis. Gabriel synthesis is named after the German

chemist Siegmund Gabriel who investigated the transformation of halide compounds

to a primary amine by N -alkylation of potassium phthalimide in 1887 [6]. Traditional

Gabriel synthesis compromise a phthalimide salt, which nucleophilicly substitutes or

eliminates the halide moiety followed by the hydrolysis of the phthalimide moiety into

a primary amine by hydrazine. Nucleophiles give more elimination reactions if their

basicity gets stronger or if the nucleophile or the halide compound gets more sterically

hindered. While long alkyl primary halides give high yields of substitution, tertiary

halides give 100% elimination product. The bromide moiety in PS is a secondary halide,

which will result in both elimination and substitution products, which was worth to

investigate quantitatively. The approaches to obtain ω-amine-functional PS primarily

synthesized via ARGET ATRP are shown in Figure 2.1

The second approach (route 2) for the ω-amine functionality was azidation followed

by reduction by LiAlH4 or by a Staudinger reaction. Azidation reactions are known to

be quantitative and easily reduced to an amine by various reducing agents in various

conditions. For instance, lithium aluminum hydride is one of the widely used reducing

agent for azide end-functional PS [7], [8]. In cases where the functional groups on the

25


Figure 2.1: Route 1(top), and Route 2 (bottom) for ω-amine-functional PS -Steps are ARGET ATRP of PS followed by gabriel reaction (route 1) or azide route (route2)

polymer are susceptible to be reduced by LiALH4, a milder reducing agent has to be

chosen for the reduction. Triphenylphosphine (P(Ph)3) is a commonly used reducing

agent used in the cases where the LiAlH4 reduction results in side reactions. However,

reduction by P(Ph)3 proceeds in two steps, in which the first step, the formation of

phosphoranimine adduct, is fast; and the second step, the hydrolysis of phosphoran-

imine by water is slow [9]. In this work, LiAlH4 and P(Ph)3 are compared as reducing

agents for the ω-azide-functional PS and P(SMI) in terms of yield and side reactions.

The third approach for the ω-amine functionality was reduction of α-nitrile func-

tionality of PS synthesized via RAFT polymerization. BMS, which is known to be a

mild reducing agent for nitrile groups and a good candidate for the selective reduction

of nitriles in the presence of dithioester, was used for the reduction of nitrile to amine

in PS with ω-dithioester functionality. The reaction was investigated in terms of yield

and side reactions. This route was an opportunity to obtain both thiol and amine

functionality from a single batch, which will have the same molar mass, distribution

and primary functionality, which could be used as constant parameters in the study

of further polymer-polymer coupling reactions. Figure 2.2 shows the reaction steps to

obtain amine end-function on a PS primarily synthesized via RAFT polymerization.

26

2.1 Introduction

Figure 2.2: Route for amine end-functional PS primarily synthesized via RAFTpolymerization - PS with a nitrile moiety is obtained after RAFT polymerization andreduction of nitrile moiety by BMS in an acidic medium

The first approach for the ω-thiol-functional polymers was S -alkylation route fol-

lowing ARGET ATRP. The aim for investigating this route was to be able to obtain

both amine and thiol functionalities from a single batch. S-alkylation of thiourea with

an alkylbromide followed by the cleavage of the formed isothiouronium salt with an

alkali is an indirect method of mercapto-de-halogenation [10]. This reaction is a well

known ancient method for the transformation of halides into thiols. Similar to the

Gabriel synthesis, nucleophilic thiourea attack gives mainly substitution for primary

halides and elimination for sterically hindered halides.

Figure 2.3: Routes for thiol end-functional PS - Aminolysis (top) and S -alkylation(bottom)

As an alternative approach to the S -alkylation, ω-thiol-functional PS and P(SMI)

were synthesized via the aminolysis of the thioester by a primary amine that nucle-

ophilicly substitutes the dithioester. The aminolysis reaction is known to give quan-

titative yields as long as oxidative coupling of thiyl anions is suppressed [11, 12, 13].

Oxidative coupling is prevented by reducing agents such as sodium bisulfate [12], TCEP

27


[14] or PBu3 [11]. Reducing agents such as zinc/acetic acid are also used to cleave the

disulfide bonds into thiols as a second step after aminolysis of the thioester moiety [15].

Figure 2.3 shows both of the approaches to obtain an thiol end-functionality in PS.

In this chapter, aiming at the synthesis of well defined high T g thermoplastics with

high amine and thiol end-functionality, different polymerization and post-polymerization

methods were compared in terms of robustness and reaction efficiency.

2.2 Experimental Section

2.2.1 Materials

Styrene (Aldrich, >99%) was vacuum distilled and stored under argon, azobisisobuty-

ronitrile (AIBN, Aldrich) was recrystallized from methanol, tris[2-(dimethylamino)ethyl]

amine (Me6TREN) was synthesized according to the literature [16], N-phenyl maleimide

(MI, Aldrich, 97%), anisole (Aldrich, 99%), toluene (Biosolve, AR), dimethylformamide

(DMF, Biosolve, AR), 1,4-dioxane (Merck, >99%), L-ascorbic acid (Sigma, >99%),

CuBr2 (Aldrich, 99%), ethyl 2-bromoisobutyrate (EBiB, Aldrich, 98%), 1-phenyl ethyl-

bromide (1-PEBr, Aldrich, 97%), thiourea (Aldrich, 99%), potassium phthalimide

(Aldrich, 98%), hydrazine monohydrate (N2H4.H2O, Aldrich, 98%), sodium azide (NaN3,

Aldrich, 99%), lithium aluminium hydride (LiAlH4, Aldrich, 95%), hydrochloric acid

(HCl, Merck, 32% in water), dichloromethane (DCM, Biosolve, AR), methanol (Bio-

solve, AR), ethanol (Biosolve, AR), n-hexane (Biosolve, AR), tetrahydrofuran (THF,

AR, Biosolve) triphenylphosphine [P(Ph)3, Aldrich, 95%], anhydrous magnesium sul-

fate (MgSO4, Sigma, >98%), 2-cyanoprop-2-yl dithiobenzoate (CIPBD, Aldrich, >97%),

cumyl dithiobenzoate (CDB, synthesized by van den Dungen [17]), dimethyl sulfide bo-

rane [BMS, BH3.S(CH3)2, Aldrich, 2 M in THF], ethanolamine (Aldrich, 99.5%), and

tributylphosphine [P(Bu)3, Aldrich, 97%] was used as received.

2.2.2 Methods

Monomer conversion in the polymerization reactions was determined by a GC450

gas chromatograph (Varian) equipped with a CP-Wax 52CB capillary column (length:

25 m; diameter: 0.4 cm) and with a glass PEG pre-column. Injection temperature was

250 ◦C, and detector temperature was 300 ◦C. Analyses were carried out according to

28


the following temperature profile: 60 ◦C for 1 min, from 60 ◦C to 100 ◦C with 10 ◦C/min

rate, from 100 ◦C to 210 ◦C with 20 ◦C/min rate, 210 ◦C for 1 min.

The 1H NMR analyses were performed on a Mercury 400, CDCl3 was used as a

solvent for all samples. 10-15 mg of sample was dissolved in 0.8 mL of CDCl3.

Number average molar mass (M n) and dispersity (D) values were measured by

Size Exclusion Chromatography (SEC) on a Waters Alliance system equipped with

a Waters 2695 separation module, a Waters 2414 refractive index detector (35 ◦C), a

Waters 2487 dual absorbance detector, a PSS SDV 5 µm guard column followed by 2

PSS SDV linearXL 5 µm columns (8 mm * 300 mm) in series at 40 ◦C. Tetrahydrofuran

(THF stabilized with BHT, Biosolve) with 1% (v/v) acetic acid was used as eluent at a

flow rate of 1.0 mL/min. The molar masses were calculated with respect to polystyrene

standards (Polymer Laboratories, M p = 580 Da up to M p = 7.1x106 Da). The samples

were dissolved in eluent solution with a concentration of 1 mg/mL and filtered through

a 0.2 µm PTFE filter (13 mm, PP housing, Alltech).

MALDI-TOF-MS analysis were performed on a Voyager DE-STR from Applied

Biosystems equipped with a 337 nm nitrogen laser with an accelerating voltage of 25

kV. The cationizing agent was either silver trifluoroacetate (Aldrich, 98%) or potas-

sium trifluoroacetate (Fluka, >99%). Polymer samples were dissolved in THF with a

concentration of 1 mg/mL. Spectra were acquired in the reflector mode.

2.2.3 Synthesis of PS and P(SMI) with ω-amine Functionality

2.2.3.1 ω-Bromide-functional PS

A dry Schlenk flask was charged with CuBr2 (0.0108 g, 0.0482 mmol) and ascorbic

acid (0.0849 g, 0.482 mmol) and filled by argon gas. In a separate flask, Me6TREN

(0.1109 g, 0.482 mmol) was dissolved in 1-2 mL anisole and added to the reaction

flask. The formation of copper complex was observed by the yellowish green color of

the solution. 15.06 g of monomer (styrene)(0.14 mol) and 14 mL anisole (total solvent

amount was 16.5 mL) were added to the reaction flask and the solution was degassed

for half an hour by bubbling argon through. After degassing ended, the Schlenk flask

was heated up to 90 ◦C in an oil bath. In a separate flask, EBiB (0.94 g, 4.82 mmol) was

weighed and dissolved in 1-2 mL anisole and degassed for half an hour by bubbling argon

through. The initiator solution was injected into the reaction flask. The polymerization

29


was allowed to proceed until the desired conversion was reached, and the reaction was

quenched by cooling and exposing the contents of the flask to air. The polmer in the

reaction mixture was precipitated in 160 mL of ethanol, vacuum filtrated, and the

residue was dried overnight under vacuum at 60 ◦C. In necessary cases, product was

purified from residual solvent and monomer by repeating the work-up procedure by

redissolving the polymer in THF.

2.2.3.2 ω-Amine-functional PS

Gabriel Synthesis Route Typically, ω-bromide-functional PS (2.5 g, 0.001 mol)

and potassium phthalimide (1.85 g, 0.01 mol) were dissolved in 10 mL DMF. The

mixture was stirred at 80 ◦C overnight in an argon atmosphere. The reaction mixture

was precipitated in ethanol, filtered, and dried under vacuum at 60 ◦C. The reduction

of ω-phthalimide function into an amine was done as follows: ω-phthalimide-functional

PS (2.5 g, 0.001 mol) was dissolved in 10 mL DMF and hydrazine monohydrate (0.5

g, 0.01 mol) was added. The reaction mixture was degassed with argon for 30 minutes

and heated to 80 ◦C. The mixture was stirred overnight in an argon atmosphere. After

cooling down to ambient temperature, the reaction mixture was treated with HCl to

liberate the amine. The reaction mixture was precipitated in ethanol, filtered, and

dried under vacuum at 60 ◦C.

Azide Route Typically, ω-bromide-functional PS (2.5 g, 0.001 mol) was dissolved

in 10 mL DMF, and sodium azide (130 mg, 0.002 mol) was added to the solution.

The mixture was stirred overnight at room temperature. Formed NaBr salt was fil-

tered, and the filtrate was precipitated in ethanol, vacuum filtered, and the residue

was dried overnight under vacuum at 60 ◦C. The reduction of ω-azide-functional PS

was performed via two different procedures. In the first reduction procedure, 10-fold

excess LiAlH4 (0.4 g) was dispersed in 10 mL dry THF, PS (2.5 g, 0.001 mol) was dis-

solved in 30 mL dry THF, and slowly added to the LiALH4 suspension. The solution

was stirred for 12 hours at room temperature. The excess LiAlH4 was separated by

filtration and the polymer in the filtrate was precipitated in methanol. The polymer

was filtrated and redissolved in DCM. The grey precipitate formed was filtrated over

celite, the filtrate volatiles were evaporated in a rotary evaporator and the residue was

redissolved in CHCl3, precipitated in ethanol and vacuum filtered. The product was

30


dried overnight under vacuum at 60 ◦C. In the second reduction procedure, PS (2.5 g,

0.001 mol) was dissolved in 10 mL THF/water mixture (20:1), and next P(Ph)3 (1.31

g, 0.005 mol) was added. The solution was stirred for 24 hours at room temperature

and the volatile content was evaporated in rotary evaporator, the residue was dissolved

in 40 mL toluene/water mixture (1:1), mixed until the layers were clear. The aque-

ous layer was separated and the toluene layer was extracted three times with water

(3x20 mL). The combined toluene solution was dried over MgSO4, concentrated, and

the polymer was precipitated in ethanol and vacuum filtered. The product was dried

overnight under vacuum at 60 ◦C.

2.2.3.3 α-Nitrile-functional PS

A dry Schlenk flask was charged with styrene (10.4 g, 0.1 mol), toluene (8 mL) and

CIPDB (0.44 g, 0.002 mol), and degassed for 30 minutes by bubbling argon through.

The flask was immersed in an oil bath and heated up to 70 ◦C. In a separate flask,

AIBN (0.0656 g, 0.0004 mol) dissolved in toluene (2 mL), degassed for 30 minutes

and injected into the Schlenk flask. The reaction was allowed to proceed until the

desired conversion was reached. The reaction was quenched by cooling and exposing

the content of the flask to air. The product was isolated from the reaction mixture by

precipitation in ethanol, vacuum filtered, and dried overnight under vacuum at 60 ◦C.

2.2.3.4 α-Amine-functional PS

Typically, α-nitrile-functional PS (2.5 g, 0.001 mol) was dissolved in 10 mL THF and

BH3.S(CH3)2 (0.5 mL; 2 M in THF, 0.001 mol) was added. The solution was heated to

reflux for 5 hours. After cooling to ambient temperature, the solution was treated with

1M HCl solution in THF (4 mL), and stirred at ambient temperature for 1 hour. This

step was repeated three times. The solution was concentrated up to 20% solid content,

precipitated in cold ethanol and vacuum filtered. The product was dried overnight

under vacuum at 60 ◦C.

2.2.3.5 ω-Bromide-functional P(SMI)

Copolymerization of styrene and N-phenyl maleimide was performed similarly as

stated in section 2.2.3.1. Styrene and N-phenyl maleimide monomers are used in

equimolar amounts.

31


2.2.3.6 ω-Amine-functional P(SMI)

Transformation of the bromide end-group into an amine was done via azide route

followed by the Staudinger reaction as described in subsection 2.2.3.2. Isolation of the

product was done by precipitating the polymer product in n-hexane.

2.2.4 Synthesis of PS and P(SMI) with ω-thiol Functionality

2.2.4.1 ω-Dithioester-functional PS

ω-Dithioester-functional PS was synthesized by RAFT polymerization as described

in section 2.2.3.3.

2.2.4.2 ω-Thiol-functional PS

Aminolysis Route Typically, ω-dithioester-functional PS (2.5 g, 0.001 mol) was

dissolved in 1,4-dioxane (10 mL) in a Schlenk flask, degassed for 30 minutes by argon

bubbling, P(Bu)3 (0.2 g, 0.001 mol) and 2-ethanolamine (0.6 g, 0.01 mol) were simul-

taneously injected into the flask. The solution was stirred at ambient temperature, in

an argon atmosphere for 3 hours. After precipitating in ethanol, and vacuum filtration,

collected product was dried overnight under vacuum at 60 ◦C.

S-alkylation Route Typically, ω-bromide-functional PS (2.5 g, 0.001 mol) and

thiourea (0.77 g, 0.01 mol) were dissolved in DMF (30 mL). The solution was stirred at

100 ◦C for 24 hours. 0.4 g NaOH was dissolved in 3 mL distilled water and added to the

polymer solution. The solution was stirred at 110 ◦C for an additional 24 hours. After

cooling down the reaction mixture, 0.5 mL H2SO4 (95%, 0.01 mol) was dissolved in 2

mL water and added to the reaction mixture and the solution was stirred at ambient

temperature for an additional 5 hours. The product was precipitated in ethanol, and

vacuum filtered. The product was dried overnight under vacuum at 60 ◦C.

2.2.4.3 ω-Dithioester-functional P(SMI)

ω-Dithioester-functional P(SMI) was synthesized by RAFT polymerization as de-

scribed in section 2.2.3.3. 1,4-Dioxane was used instead of toluene.

32

2.3 Results and Discussion

2.2.4.4 ω-Thiol-functional P(SMI)

ω-Thiol-functional P(SMI) was synthesized via aminolysis as described in subsection

2.2.4.2.


2.3.1 ARGET ATRP of Styrene

ARGET ATRP was found to be a robust controlled radical polymerization technique.

The presence of a reducing agent both lowers the oxygen sensitivity of the reaction,

and allows catalytic amount of copper to be used. Secondly, copper(II)bromide used

as a starting compound, is much more stable than copper(I) bromide during storage,

so that the amount of copper to be used efficiently is much precise than the ATRP

systems using copper(I), and makes the preparation steps easier. The mechanism of

ARGET ATRP is illustrated in Figure 2.4

Figure 2.4: Mechanism of ARGET ATRP - (a) activation step in main equilibrium,(b) deactivation step in main equilibrium, (c) propagation, (d) termination, (e) regenerationof Cu(I) activator

Table 2.1 shows results of different batch of ω-bromide-functional PS synthesized

with experimental details. Theoretical M n values are calculated according to the

monomer-to-initiator ratio with the conversion value calculated from the GC mea-

surements. The M n values calculated theoretically, and the values obtained from SEC

and the 1H NMR measurements may be different. There are various reasons for these

differences; emphe.g. low theoretical values with respect to the measured ones may

imply the inefficiency of the initiating step, high theoretical values with respect to the

33


measured ones could be thermal initiation. However, the theoretical values calculated

and measured are in rather good agreement with each other.

Lower concentration of active radical chains results in lower D values. The sample

PS4 has a higher D value than the other samples in the table indicating poor control

of the active chains and termination. Kinetic plots of the PS2 and PS4 show that

termination reactions are more significant, and PS4 having higher molar mass shows

higher dispersity. Figure 2.5 shows the ln([M]0/[M]t) vs. time curves of these two

reactions compared with those of the reactions PS8 and PS9.

Table 2.1: ω-bromide-functional PS samples synthesized via ARGET ATRP

Sample [Mon]:[Ini] Time Conversion Initiator M n M n M n Functionality D(h) (%) used (theo) (SEC) (1H NMR) (%)(1H NMR) (SEC)

PS1 30:1 24 60 EBiB 1874 2155 2770 93 1.14PS2 93:1 90 46.5 1-PEBr 5580 5542 7664 90 1.15PS3 30:1 25 53 1-PEBr 1590 1766 2523 94 1.17PS4 207:1 70 56 1-PEBr 12048 11017 13206 76 1.4PS5 48:1 4 34 1-PEBr 1784 1424 1737 90 1.13PS6 96:1 21.5 45 1-PEBr 4500 4396 4083 97 1.11PS7 192:1 21.5 23 1-PEBr 4600 4930 5249 99 1.17PS8 29:1 49 93 EBiB 2842 3317 4155 93 1.13PS9 29:1 49 93 EBiB 2842 2938 3530 90 1.15

All ARGET ATRP reactions are performed with [ini]:[Cu(II)Br2]:[Me6TREN]:[Asc.A.]

of 1 : 0.01 : 0.1 : 0.1. End-functionality yields were calculated according to the ra-

tio of signals of initiating group and signal of the gemini proton next to the bromide

moiety (see Figure 2.1 for structures). Two different ATRP initiators were used in

ARGET ATRP of styrene. One is EBiB, which has a methylene group adjacent to the

ester moiety. Methylene group has a signal at around 3.5 ppm and this signal does

not overlap with any other signals of the polymer. 1-PEBr has a methyl group with

a signal at 1.0 ppm, which is slightly overlapping with the methylene signals of the

main chain. This overlap increases the uncertainity in calculating the extent of func-

tionality and M n values by 1H NMR. The extent of this error depends on the average

chain length of the polymer. For instance, PS5 sample has a lower M n value and in

the 1H NMR spectrum of the sample overlapping is less significant than in the case

of PS6 sample. Nevertheless, integration in the 1H NMR spectra itself has a 5% error

in standard measurements, additionally poor signal to noise ratio in integrating the

signals of end-functionalities and initiating moieties in polymers increases this error.

The results found in the 1H NMR spectra of PS synthesized with 1-PEBr are in 10%

error window that we find adequately accurate. MALDI-TOF measurements show the

34


10 20 30 40 50 60 70 80 90 100

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

ln([

M] 0

/[M

] t)

time (h)

0.9514

PS2

20 30 40 50 60 70

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

ln([

M] 0

/[M

] t)

time (h)

0.97482

PS4

0 10 20 30 40 50

0.0

0.5

1.0

1.5

2.0

2.5

3.0

ln([

M] 0

/[M

] t)

time (h)

0.98703

PS8

0 10 20 30 40 50

0.0

0.5

1.0

1.5

2.0

2.5

3.0

ln([

M] 0

/[M

] t)

time (h)

0.9989

PS9

Figure 2.5: ln([M]0/[M]t) vs time plots of ARGET ARTP reactions - PS2 (topleft), PS4 (top right), PS8 (bottom left) and PS9 (bottom right) with R2 values of thelinear fits

presence of bromide moiety qualitatively, but MALDI-TOF data is not quantitative

due to the uncontrolled selective ionization of the chains. Therefore, the 1H NMR data

is the most efficient of all possible quantitative characterization methods.

2.3.2 Transformation of Bromide Moiety to Amine in PS

Polymers that are synthesized via ARGET ATRP have a halide moiety as an ω-

function. The polymers synthesized in this study have a bromide moiety. Transfor-

mation of the bromide moiety into an amine was possible via a number of different

approaches. First approach (route 1) was the Gabriel synthesis, i.e. the alkylation of

the bromide function with a phthalimide, followed by the deprotection with hydrazine,

which gives the ω-amine functionality. As an alternative to the Gabriel synthesis, a

second approach (route 2) was followed. This was the azidation of the bromide moi-

ety, followed by the reduction of the azide into an amine. Figure 2.1 is illustrating

both routes performed for the synthesis of amine end-functional PS in the introduction

section.

35


In route 1, the reaction products of the transformation of bromide into phthalimide

were found to be 45% ω-phthalimide function and 55% PS with unsaturated end-group,

according to the 1H NMR analysis. The main reason for the low yield was the low

nucleophilic activity of the phthalimide against the secondary alkyl bromide moiety and

the preference of an elimination reaction instead of an SN2 reaction. The competition

between an SN2 and an elimination reaction is affected not only by the position of the

halide, but also by the solvent used in the reaction and by the reaction temperature.

DMF and THF are two solvents, which are suitable for the minimization of elimination

reactions due to their appropriate polarity index values for this reactions. In this study,

DMF was chosen since it has been found to be more efficient for substitution than THF

due to the moderate solubility of potassium phthalimide [18]. Despite the use of DMF,

there is relatively much elimination product, which is probably due to the fact that the

terminal bromide is secondary.

In route 2, bromide functionality of PS that was synthesized with the same ARGET

ATRP procedure, was transformed into an azide, and the azide moiety was reduced to

an amine with a reducing agent where two different reducing agents are comparatively

used. LiAlH4, which is a powerful reducing agent, was used succesfully for the reduction

of azide by Fallais et al. [7]. In addition, the ester moiety of the EBiB initiator present

as an α- function was reduced to an alcohol as a side reaction.

The 1H NMR spectrum of PS-N3 (Figure 2.6), shows the quantitative transforma-

tion of the bromide moiety into azide without any side reactions. In the spectrum

of PS-NH2 that was obtained by the LiAlH4 reduction, reduction of ester moiety was

observed as a side reaction. The signals at 2.9 ppm and 0.6 ppm were assigned to the

reduction product of the initiating ester moiety.

The (partial) reduction of the ester moiety leads to problems in the quantification

of the ω-amine function via 1H NMR due to the disappearance of the shifts of gem-

ini protons adjacent to the ester group, which are labeled in comparative 1H NMR

spectra of PS-N3. Moreover, an α-hydroxy functionality may interfere later on with

the intended amine-anhydride coupling reaction. The solution to the problem could

be either change of the initiator used, or using a milder reducing agent that selectively

reduces the azide function in the presence of an ester moiety. Both approaches were

investigated, since both of them have their own advantages. A milder reducing agent,

P(Ph)3, was studied since the signal of the initiating group, the methylene group on the

36


ppm (t1)1.02.03.04.0

ppm (f1)1.02.03.04.0

(i)

(ii)

a b

c

d

d

e

DMF

Figure 2.6: Comparative 1H NMR spectra of PS-NH2 (i) and PS-N3 (ii) -Signal assignments are as follows: (a) gemini proton adjacent to azide moiety, (b) twogemini protons adjacent to ester moiety (initiating group), (c) two methyl groups adjacentto the ester moiety, (d) two gemini protons adjacent to hydroxy group (reduction productof the ester moiety), (e) two methyl groups of the 2-dimethyl alcohol moiety

37


ester moiety, is an isolated chemical shift at 3.6 ppm. Therefore the functionality yield

can be calculated precisely by using EBiB initiator. An alternative initiator, 1-PEBr

was also tried, since the hydrolysis of phosphoranimine was expected to be incomplete.

Another reason to use 1-PEBr as an alternative initiator was the fact that methylene

group on EBiB initiator will not give a significantly separate shift in the intended amine

functional P(SMI) synthesis, since the main chain shifts of P(SMI) copolymer overlap

with the ester methylene shift. Comparative 1H NMR spectra of PS-Br synthesized

with EBiB initiator, its azide and amine end-functional derivatives, and the amine

derivative reacted with trichloroacetyl isocyanate (TAI) are shown in Figure 2.7 with

the corresponding structures and labeled protons. The reduction of azide was done

with P(Ph)3. In spectrum labeled as (iv), there’s seen 3 signals labeled as (e) which

are the aromatic groups of P(Ph)3. Since they have a weaker signal in the spectrum of

PS-NH2, which is labeled as (iii), they are suggested to be nucleophilicly substituted

by excess TAI, while a carbodiimide moiety forms at the ω position of PS, and P(Ph)3

leaves as an oxide [19].

The azide route with P(Ph)3 reduction was also performed with PS-Br that is

synthesized with 1-PEBr. Quantitative yields were obtained for this reaction as well.

SEC measurements have shown that hydrodynamic volume is affected by the mod-

ification of the end-groups, which is observed in the SEC measurements of low molar

mass PS (see Figure 2.8) more significantly compared to relatively high molar mass PS.

In the same figure, the high molar mass shoulder observed in the SEC traces of PS-

NH2 is the product formed during the reduction of the azide moiety by P(Ph)3. The

molar mass of the shoulder is exactly two times of that of the main peak, which implies

the combination of the two functional chain ends. Shoulder formation was observed in

both PS samples prepared by EBiB and 1-PEBr. This phenomenon could be due to the

coupling of two azide functional chains during the transition state that is illustrated in

Figure 2.9.

Two azide functional PS chains conjugate in the presence of a phosphine, where

the phosphine is complexing with azide groups from two PS chains. The transition

states of phosphoranimine formation was described in Leffler and Temple’s work [21].

It is observed that stirring the reaction for a longer time in a THF-water mixture

improves the dissociation of the conjugated chains. Presence of water as a proton source

throughout the reaction was credited to decrease the extent of coupling. Reduction with

38


ppm (t1)

1.02.03.04.05.06.07.08.0

ppm (t1)

1.02.03.04.05.06.07.08.0

ppm (t1)

1.02.03.04.05.06.07.08.0

ppm (t1)

1.02.03.04.05.06.07.08.0

a

a

a

a

b

b, c

b

b

c

c

c

d

e

f g

(i)

(ii)

(iii)

(iv)

Figure 2.7: Comparative 1H NMR spectra of the steps of azide route followedby Staudinger reaction with corresponding structures - Spectra are as follows:PS-Br(i), PS-N3(ii), PS-NH2(iii) and PS-NH2 treated with TAI(iv), (a) methyl groupsadjacent to the ester, (b) methylene group adjacent to ester, (c) gemini proton adjacent toend-functionality, (d) hydrolysis product of TAI [20], (e) triphosphine oxide (see the text),(f) proton of the first amide group of TAI, (g) proton of the second amide group of TAI

3.0 3.5 4.0 4.5

0.0

0.5

1.0

dwt/d

(logM

)

log M

PS-N3 PS-NH2 PS-Br

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2

0.0

0.5

1.0

dwt/d

(logM

)

log M

PS-N3 PS-NH2 PS-Br

Figure 2.8: Comparison of SEC traces of ω-bromide-functional PS and its azideand amine derivatives - The samples are PS3 with a M n of 2000 g/mol (right) and PS2with a M n of 5500 g/mol (left) (Table 2.1)

39


Figure 2.9: Phosphoranimine formation during azide-phosphine reaction - Illus-tration of the transition states during phosphoranimine formation

LiAlH4 gives quantitative yields as well and no coupling of chains were observed in SEC

measurements. Therefore, ω-amine-functional PS would be preferred to be synthesized

by LiAlH4 reduction due to the disadvantage of problematical hydrolysis step of P(Ph)3

reduction. However, LiAlH4 is a strong reducing agent, which wouldn’t be preferred in

the synthesis of ω-amine-functional P(SMI) that will likely give side reactions with the

imide carbonyls.

2.3.3 Transformation of Bromide Moiety to Thiol in PS

ω-Thiol-functional PS was synthesized from PS-Br synthesized by ARGET ATRP by

S-alkylation of the bromide end-group followed by the hydrolysis of the isothiouronium

salt formed. Yield of the thiol functionality, which was calculated from the 1H NMR

spectrum, was 60%. S-alkylation was complete, but not only the substitution product

formed but also did the elimination product. Hydrolysis of the isothiouronium salt was

not complete and thiouronium moiety was observable both in 1H NMR and MALDI-

TOF-MS analysis. Figure 2.10 shows the comparative the 1H NMR spectra of ω-

bromide-functional PS and ω-thiol-functional PS, where all signals of end-groups are

assigned.

Intended nucleophilic substitution of bromide by thiourea also gives elimination

products due to the secondary bromide moiety at the end of the chain, which is observed

in Gabriel reaction as well, with an adjacent phenyl ring increasing the steric hindrance.

40


ppm (t1)

0.01.02.03.04.05.06.07.08.09.0

ppm (t1)

0.01.02.03.04.05.06.07.08.09.0

d,e

(i)

(ii) a b

c d

f

(i) (ii)

a b

c d

e

f

Figure 2.10: Comparative 1H NMR of PS-Br (i) and PS-SH (ii) - Signal as-signments: (a) acidic protons of amine group of isothiouronium moiety (ii), (b) terminalproton of unsaturated end-group (ii), (c) gemini proton adjacent to bromide moiety (i),(d) methine protons adjacent to ethylester-α function (i,ii), (e) gemini proton adjacent toisothiouronium moiety (ii), (f) gemini proton adjacent to thiol moiety (ii)

41


Eventually, modification of the bromine moiety into a thiol in a two-step reaction,

which is a relatively laborious technique with a maximum 60% functionalization yield,

was not sufficiently successful for the utilization of the building blocks synthesized with

this technique further in intended thiol-ene coupling reactions. The synthesis of ω-thiol-

functional PS via aminolysis of dithioester moiety, which would be primarily obtained

by RAFT polymerization, was decided to be investigated as an alternative approach.

2.3.4 RAFT Polymerization of Styrene

PS was synthesized via RAFT polymerization where AIBN has been used as a radical

initiator and dithiobenzoate with a cyanoisopropyl leaving group as a RAFT agent.

This procedure leads to a polymer with a dithiobenzoate moiety as an end-function and

cyanoisopropyl moiety as an initiating function. The main difference between RAFT

polymerization and ATRP in terms of kinetics is the initiation behavior and equilibrium.

The mechanism of RAFT polymerization is shown in Figure 2.11. As shown in this

figure, the initiation is actually the same as the initiation in conventional free radical

polymerization (reaction Ia and Ib). Additional to the conventional initiation, in RAFT

polymerization, the R group on the chain transfer agent (CTA) homolytically cleaves

during chain transfer and reinitiates new chains (reaction IIIb). The amount of CTA

relative to the radical initiator is large, so that the theoretical molar mass is accepted

to be calculated based on the molar ratio of monomer to CTA. This actually means

that the number of chains initiated by radical initiator is negligible relative to the

number of chains initiated by CTA. The conventional initiation continues throughout

the polymerization, which leads to the observation of low molar mass tailing in SEC

analysis. These initiation phenomena leads to higher D values, also due to the non-

stoichiometric amounts of initiating groups and CTA, termination reactions becomes

more significant in longer reaction times at high conversions.

The reason for relatively higher dispersity than a principally expected value are

the relatively large time constants in the pre-equilibrium (IIa and IIb) and the core

equilibrium (IV) between the active propagating radicals and dormant chains as Moad

and coworkers described [22], which inhibits the equal probability for all chains to grow

simultaneously. RAFT polymerization has been chosen for the synthesis of ω-thiol-

functional PS since the hydrolysis of the dithioester to a thiol is the most convenient

way to obtain a high thiol end functionality. Besides, usage of CIPDB as a CTA results

42


Initiator I

I. Initiation

Imonomer

P1

II. Pre-equilibrium

(Ia) (Ib)

Pm

SS

Z

R SS

Z

RPm SS

Z

PmR

RSS

Z

R SS

Z

RR

III. Propagation

(IIa)

(IIb)

Pnmonomer

Pn+1 (IIIa) Rmonomer

P1 (IIIb)

IV. Core equilibrium

Pn

SS

Z

Pm SS

Z

PmPn SS

Z

PnPm

V. Termination

Pn Pm Pn+m (Va) Pn Pm (Vb)Pn Pm

R R R-R (Vc) Pn I Pn (Vd)

Pn R Pn (Ve)

(IV)

Figure 2.11: Fundamental reaction stpes in the RAFT process - (Ia) dissociationof the initiator, (Ib) first monomer addition, (IIa, IIb) initial addition-fragmentation equi-librium, (IIIa) main propagation, (IIIb) reinitiation, (IV) main addition-fragmentationequilibrium, (Va) termination by combination of growing chains, (Vb) termination bydisproportionation of growing chains, (Vc) termination by combination of fragmented Rgroups, (Vd) termination by combination of growing chain and dissociated initiator, (Ve)termination by combination of growing chain and fragmented R group

43


in a nitrile-α-functional PS that can be further reduced to an amine function in one

step. Table 2.2 shows the results of different batches of ω-dithioester-functional PS

synthesized.

Table 2.2: ω-dithioester-functional PS samples synthesized via RAFT polymerization

Sample [Mon]:[CTA] Time Conversion M n M n M n Functionality (%) D(h) (%) (theo) (SEC) (1H NMR) (1H NMR) (SEC)

PS1 20:1 7 46 960 1147 1374 75 1.19PS2 20:1 16 32 865 1202 1270 73 1.11PS3 40:1 10 37 1541 2131 2291 68 1.2PS4 96:1 38 41 4100 6585 7123 70 1.25PS5 48:1 46 38 1900 4226 3895 70 1.25PS6 24:1 46 37 925 1892 2228 74 1.17PS7 40:1 29 26 1083 1704 1597 79 1.12PS8 80:1 48 31 2582 3445 3631 74 1.16PS9 160:1 48 35 5832 7105 7285 65 1.21PS10 285:1 40 32 9522 15967 15800 72 1.38PS11 20:1 24 42 874 976 1312 85 1.12

RAFT polymerization has two types of initiation: one is the ”initiation” taking

place by the attack of an initiator-derived primary radical to the monomer and the

other is the ”reinitiation” where the R group of the CTA homolytically cleaves during

the chain transfer and initiates a new chain by attacking to the monomer. These two

different initiation processes produce two different types of polymer one of which is

initiated by the thermal initiator and other is initiated by the CTA. All polymerization

reactions are performed at 70 ◦C at which AIBN has a halflife time of 10 hours. For

the polymerizations in which the reaction time is less than 30 hours, initiation con-

tinues throughout the polymerization by thermally cleaved initiator radical. McLeary

et al. have shown that CIPDB is completely consumed after 50 minutes in styrene

polymerization performed at 70 ◦C with AIBN [23] where the amount of CTA was 8

times of that of AIBN. In this study, the amount of CTA was 5 times that of AIBN,

which means the consumption time should be shorter. This fact implies that at least

70% of the PS chains were formed by reinitiation in all polymerizations performed, and

the rest of the chains were initiated by AIBN. Therefore, measured M n values would

be expected to be lower than the theoretical values. However, calculated theoretical

values are lower than the calculated value from the 1H NMR spectra, implying at first

that the initiation and reinitiation were not efficient. This could be only due to the

impurities present in both CTA and AIBN. The M n values from SEC measurement

were calculated according to PS standards. End-groups affect the retention time, thus

44


influence the M n value. Therefore, a systematic error due to the interaction of chain-

end functionalities with the stationary phase should be taken into account for SEC

measurements. There were no anomalies observed in the SEC traces and D values

were in the expected range for RAFT polymerization of styrene. The kinetic plots of

the reactions with a reaction time longer than 30 hours, in which the AIBN present

in the reaction mixture was mostly consumed (>75%), showed more termination than

the reactions quenched at shorter times. Therefore, it is concluded that CIPDB is not

dynamic enough to maintain a constant radical concentration.

The resulting polymers have 100% nitrile-α function as a result of the nitrile moi-

ety present both in CIPDB and AIBN. Terminal functionality and M n values of the

PS samples were calculated according to the 1H NMR analysis. Dithioester terminal

functionality were calculated according to the ratio of the area of the methyl protons

adjacent to the nitrile-α function (Aα) to the ortho protons of the ω-thiobenzoate func-

tion (Aω). M n values were calculated according to the ratio the area of the aromatic

proton signals of the main chain (Ap), respectively. An example of 1H NMR spectrum

of sample PS7 is shown in Figure 2.12 with integration results of the signals and the

formulas are:

%functionality =Aω/2

Aα/3(2.1)

Mn =Ap/5

Aα/3∗M(styrene) (2.2)

2.3.5 Transformation of Nitrile Moiety into Amine in PS

As stated in the previous subsection, PS synthesized with RAFT polymerization

has a nitrile moiety in the initiating group (α-function). The nitrile function can be

reduced to an amine by BH3.S(CH3)2 (BMS) in one step [24]. The transformation of

the nitrile moiety into an amine (Figure 2.2) was investigated as a third approach to

obtain amine-end-functional PS. This route was an opportunity to obtain an amine

function in a one-step post-polymerization process. Figure 2.13 shows the comparative

1H NMR of nitrile-α-functional PS-RAFT and PS product treated with BMS.

BMS is known to be an effective reducing agent for carboxylic acids, esters, primary

amides and nitriles [25]. Reactivity of BMS towards esters is lower than towards the

45


a

b

c

a

b

c

Figure 2.12: 1H NMR spectrum of sample PS7 - (a) ortho protons of the ω-thiobenzoate function (Aω), (b) aromatic protons of the main polymer chain (Ap), (c)methyl protons adjacent to the nitrile-α function (Aα)

ppm (t1)

0.501.001.502.00

ppm (t1)

0.501.001.502.00

a

a b c

(i)

(ii)

a b c

Figure 2.13: Comparative 1H NMR spectra and corresponding structures - (i)nitrile-α-functional PS and (ii) PS reduction product, (a) methyl signals adjacent to nitrile,(b) methyl signals adjacent to imine, (c) methyl signals adjacent to methylamine

46


acids and nitriles. This fact serves the possibility of selective reduction of nitriles in the

presence of dithioesters. Dithioesters are also known to be readily reactive towards both

electrophiles and nucleophiles. However, to the best of the author’s knowledge, there

is no study reported on reduction of dithioesters by BMS in literature. In the study

of reduction of PS-RAFT with a nitrile-α function, BMS reaction followed by an acid

treatment was performed to transform nitrile function into a methyl amine. SEC traces

of reaction samples show that there is shoulder formation. Increase in the molar mass

could imply both disulfide and borazine formation [25]. Disulfide formation should

exactly double the molar mass calculated from SEC measurements, while borazine

forms a three-arm-star structure, which will not be seen as a double or triple molar

mass in SEC traces. The 1H NMR analysis (Figure 2.13) showed that there are amine,

imine and nitrile end-groups and SEC measurements showed that there is an increase

in the molar mass more than a double, which means there is a conjugation between

two or more polymer chains due to complexation between boron and nitrogen and

disulfide formation. Acid treatment did not break the conjugation, which strengthens

the possibility of disulfide formation. Therefore, the reduction of the nitrile moiety was

performed with a PS-SH as well in which the dithioester moiety was already transformed

into thiol by aminolysis. Acid treatment was successful according to SEC traces that are

shown in Figure 2.14. However, after isolation of the product, the 1H NMR spectrum

showed that reduction to an amine was not complete, the signals concerning the imine

moiety were still present. SEC trace of the isolated product showed the remaining

shoulder at higher than a double molar mass, which implies the conjugation remains.

Figure 2.14 shows the effect of acid treatment after the shoulder has formed. Upon

addition of HCl to the reaction, the shoulder is disappearing. The molar mass corre-

sponds of the peaks calculated are around 3000 and 8500, which also implies that there

is a complexation where more than 2 chains are involved.

2.3.6 Transformation of Dithioester Moiety into Thiol in PS

Aminolysis is a type of transesterification reaction where the nucleophilic amine

attacks to the carbonyl of the ester and forms an amide and a primary alcohol by

the migration of one of the acidic protons of the amine. This mechanism works for

thioesters as well. Figure 2.15 illustrates the thiol formation by the aminolysis of a

dithioester.

47


2.5 3.0 3.5 4.0 4.5 5.0 5.5

0.0

0.2

0.4

0.6

0.8

1.0

dw

t/d

(lo

gM

)

(no

rma

lize

d)

logM

(a)

(b)

(c)

(d)

Figure 2.14: SEC traces of the follow up of the reduction of the nitrile moietyon PS-SH by BMS - (a)before the acid treatment, (b) after the first HCl addition, (c)after the 2nd HCl addition , (d) after the 3rd HCl addition

S Z

S

R1

R2 NH2S

R1

Z

S

HN

R2

H

R1 SHZ

S

NH

R2

Figure 2.15: Mechanism of aminolysis reaction - The reaction takes place by thenucleophilic substitution of amine with the thiyl group of the thioester

48


The intermediate thiyl anion is susceptible to oxidation and can eventually produce

disulfides by oxidative coupling. Molecular oxygen or a high pH could trigger disulfide

formation. During aminolysis of the dithioester moiety, trace amounts of oxygen in

the reaction mixture induce disulfide formation. P(Bu)3 is a common reducing agent,

which is used in aminolysis reactions to suppress disulfide formation.

The 1H NMR spectra and SEC traces show that the aminolysis of the thioester

moiety is complete and no disulfide formation takes place in PS samples. The cleavage

of the dithiobenzoate moiety was indicated by the immediate color change from pink

to yellow. After vacuum filtration of the precipitate, the residue was a white powder

while the filtrate was a yellow solution. The yellow color is due to the formation of

the thioamide. Figure 2.16 shows the disappearance of the dithioester signals in the

1H NMR spectrum and Figure 2.17 shows the SEC traces of the same batch where no

disulfide formation takes place.

ppm (t1)6.507.007.508.008.50

ppm (t1)6.507.007.508.008.50

(i)

(ii)

a b

c

(i)

(ii)

a

b

c

c

Figure 2.16: 1H NMR spectra of PS-RAFT(i) and PS-SH(ii) - (a) ortho protonsof the benzoate, (b) para proton of the benzoate, (c) aromatic protons of the PS mainchain

49


2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

0.0

0.2

0.4

0.6

0.8

1.0d

wt/d

(lo

gM

)

log M

PS-RAFT

PS-SH

Figure 2.17: SEC traces - ω-dithioester-functional PS (black) and ω-thiol-functionalPS (red)

2.3.7 ω-Amine-functional P(SMI)

ω-Amine-functional P(SMI) was synthesized by ARGET ATRP of styrene with N-

phenyl maleimide followed by the transformation of the bromide moiety into an azide

and the reduction of the azide into an amine. In the copolymerization of styrene

and phenyl maleimide, monomers exhibit low reactivity ratios (<<1) due to the charge

transfer complex formation [26]. These two monomers give alternating copolymers even

where non-stoichiometric amounts of monomers are incorporated into the polymeriza-

tion reaction in case of both free radical polymerization conditions [27] and ATRP [28].

Table 2.3 shows two examples of copolymerizations of styrene and N-phenyl maleimide.

P(SMI)1 was synthesized with 10% excess amount of N-phenyl maleimide, and P(SMI)2

was synthesized with 20% excess styrene intending to compare the alternating fashion

by MALDI-TOF-MS. The MALDI-TOF-MS spectrum of P(SMI)1 (Figure 2.18) and

PSMI2 (Figure 2.19) show the constitutional fashion of the repeating units. The sam-

ples were ionized by potassium.

Table 2.3: ω-bromide-functional P(SMI) samples synthesized via ARGET ATRP

Sample [Mon]:[ini] Time Conv. M n M n M n D(h) (%) (theo) (SEC) (MALDI-TOF-MS) (SEC)

P(SMI)1 68:1 2.5 65 6008 6302 6137 1.66P(SMI)2 30:1 4.5 45 2125 1984 3741 1.49

50


799.0 2639.4 4479.8 6320.2 8160.6

Mass (m/z)

0

10

20

30

40

50

60

70

80

90

100

%In

ten

sit

y

1703.2 1708.8

Mass (m/z)

1703.2 1708.8

Mass (m/z)

1368.0 1611.8 1855.6 2099.4 2343.2 2587.0

Mass (m/z)

0

3725.0

0

10

20

30

40

50

60

70

80

90

100

%In

ten

sit

y

4st+

5m

i

5st+

5m

i

5st+

6m

i

7st+

7m

i

6st+

7m

i

6st+

6m

i

1st

1mi

Mass (m/z)

Mass (m/z)

Mass (m/z)

% in

te

nsity

% in

te

nsity

1611.8 1855.6 2099.42343.2

Figure 2.18: MALDI-TOF-MS spectrum of P(SMI)1 - Full spectrum (top), zoomin the region 1400-2600 (bottom left), and the comparison of signal shape of the measuredand calculated (bottom right)

51


599.0 2479.4 4359.8 6240.2 8120.6 10001.0

Mass (m/z)

0

4007.0

0

10

20

30

40

50

60

70

80

90

100

%In

ten

sit

y

1422.2 1426.4 1430.6

Mass (m/z)

1422.2 1426.4 1430.6

Mass (m/z)

1360.0 1613.2 1866.4 2119.6 2372.8 2626.0

Mass (m/z)

0

4007.0

0

10

20

30

40

50

60

70

80

90

100

%In

en

sit

y

4st+

5m

i

5st+

5m

i

5st+

6m

i

6st+

6m

i

Mass(m/z)

% intensity

% intensity

Mass(m/z)Mass(m/z)

1613.2 1866.4 2119.6 2372.8


The MALDI-TOF-MS spectra of both P(SMI)1 and P(SMI)2 show an alternating

fashion. In figures 2.18 and 2.19, the repeating units are shown. While the intensity

of the signals of perfectly alternating chains is the largest, the signals of the diads of

styrene or maleimide units are also present with a much lower prevalency. However,

there are no signals of chains in which there are two styrene or MI units more than the

other. These results are in agreement with the literature concerning the domination of

alternating fashion in non-stoichiometric feed of monomers [27] [28].

The bromide end-group ofthe polymer dissociates during the ionization, signals

showing up in the spectra of the P(SMI) samples are assigned to the chains with unsat-

urated ends. There is a distribution observed in the spectrum where the bromide end

group was not dissociated. None of the applied analysis methods could quantitatively

indicate the extent of end-functionality of the synthesized P(SMI) samples. FTIR could

be a method to quantitatively measure the extent of desired end functionality. How-

ever, the exact molar mass is not known, therefore the value found from FTIR analysis

would not be more than a rough estimate. The 1H NMR gives a rough implication of

the functionality yield, since the shift of the gemini proton of the bromide moiety is

52


visible.

From the procedures applied to the bromide-end function in PS, shown in Figure

2.1, azide route followed by P(Ph)3 reduction, which gave the highest yield, was also

applied for the transformation of bromide-end functionality in P(SMI) into an amine.

The first step, which is the transformation from bromide to an azide was successful

according to the 1H NMR measurements. A color change was observed during the

reaction, which may imply the interaction of NaN3 with the imide ring carboxyl groups.

No coupling was observed in SEC measurements. Reduction of the azide into an amine

was performed with P(Ph)3. Reduction with LiAlH4 was not performed since LiAlH4

is known to be a strong reducing agent that will reduce any type of carbonyl group

and also imides [29]. Reduction was done by Staudinger reaction. The first part of the

procedure was the same as the reduction of PS, however the separation of phosphine

oxide and the polymer product was not possible by extraction using a toluene-water

mixture. P(SMI) does not dissolve in toluene. The isolation of the product was done

by precipitation in n-hexane. Amine functionality was observed in the 1H NMR as

well as in MALDI-TOF-MS spectra. Comparison of 1H NMR signals of different ω-

functionalities of P(SMI) is shown in Figure 2.20. Calculated amine functionality yield

from the 1H NMR spectrum was 56%. SEC traces showed no high molar mass shoulder.

2.3.8 ω-Thiol-functional P(SMI)

One of the motivations to investigate the RAFT polymerization route was the syn-

thesis of P(SMA) copolymer. However, due to the failures in post-polymerization

reactions, the P(SMA) route was totally left. Instead of anhydride, a more stable,

resistant group against nucleophilic attacks but still with a high T g, MI was chosen for

the copolymerization studies.

RAFT copolymerization of styrene and MI showed a higher propagation rate than

the homopolymerization of PS. A coversion higher than 60% was reached in three

hours. Table 2.4 shows the reaction parameters and the characterization results of

RAFT polymerization of P(SMI). The molar ratio of monomer to CTA was given

according to the total monomer amount of styrene and MI. The molar mass of the

copolymers was measured by SEC and MALDI-TOF-MS. The real molar mass of the

copolymer was measurable neither by 1H NMR due to the overlapping of the methyl

53


ppm (t1)4.505.005.50

ppm (t1)4.505.005.50

ppm (t1)4.505.005.50

ppm (t1)4.505.005.50

a

a b

b

c

c

(i)

(i) (ii)

(ii)

(iii)

(iii)

(iv)

(iv)

Figure 2.20: 1H NMR signals of different ω- functionalities of P(SMI) -(i) ω-bromide-functional P(SMI), (ii)ω-azide-functional P(SMI), (iii) ω-amine-functionalP(SMI), ω-amine-functional P(SMI) reacted with TAI

54


peaks of the initiating function with the main chain methylene signals, nor by SEC due

to the calibration settings according to PS standards. However, MALDI-TOF-MS gave

an indication for the real molar mass, which could be compared with SEC results and

theoretical values. Although, the mass discrimination is a reality in MALDI-TOF-MS

analysis, there is a general agreement that MALDI average molar masses are accurate

for samples with low dispersity [30]. MALDI-TOF additionally gives an qualitative

information about the end groups and the topology of the chain.

Table 2.4: ω-dithioester-functional P(SMI) samples synthesized via RAFT polymerization

Sample [Mon]:[CTA] Time Conv. M n M n M n D(h) (%) (theo) (SEC) (MALDI-TOF-MS) (SEC)

P(SMI)3 22:1 3 67 4525 3374 5063 1.17P(SMI)4 100:1 3 61 11092 5746 9478 1.21

P(SMI)3 has been synthesized with 20 molar % excess styrene, and P(SMI)4 has

been synthesized with equimolar amounts of styrene and N-phenyl maleimide. Con-

stitutional analysis was done by MALDI-TOF-MS measurements. P(SMI)3 was syn-

thesized with CIPDB. In P(SMI)3, the dithioester end-functionality dissociated during

the MALDI-TOF-MS analysis and the spectrum of hydrogen-terminated product was

observed. However, there was another distribution observed, which complicated the

spectrum. Different distributions hamper the correct analysis for the constitutional

structure of the copolymer. P(SMI)4 was synthesized with CDB which was used as a

CTA. In MALDI TOF MS analysis, P(SMI)4 sample has also shown different distribu-

tions with signals overlapping each other. In this sample, the distributions were also

due to chains initiated separately by AIBN and CTA. Despite the fact that it was pos-

sible to follow the alternating chains in the spectrum, the effect of non-stoichiometric

monomer feed on the constitution of the chains was not clearly detectable. Figure

2.21 shows the MALDI-TOF-MS analysis results of the P(SMI)3. The molar mass of

this polymer was low enough to observe the overlapping peaks more clearly. Addition-

ally, the initiating group on AIBN and CTA were the same, decreasing the number of

distributions due to different end groups.

The distributions due to different end groups were concluded to be due to poor ion-

ization of dithioester moiety and producing different types of end functionalities during

the MALDI-TOF-MS measurements. In Figure 2.21, the calculated peak compared to

55


799.0 2639.4 4479.8 6320.2 8160.6 10001.0

Mass (m/z)

0

3340.0

0

10

20

30

40

50

60

70

80

90

100

2478.2 2483.8

Mass (m/z)

2478.2 2483.8

3228 3423 3618 3813 4008 4203

Mass (m/z)

0

3306.1

0

10

20

30

40

50

60

70

80

90

100

1st

1mi

Mass (m/z)

% in

ten

sit

y%

inte

nsit

y


56


measured one was for the chain with a dithiobenzoate moiety. However, that calculated

fraction is not the prevalent fraction.

The ratio of the areas of main chain methylenes and aromatics in the 1H NMR

spectrum gives an indication about the composition of the polymer chain. Spectra of

both P(SMI)3 and P(SMI)4 showed stoichiometric amounts of styrene and N-phenyl

maleimide. MALDI-TOF-MS measurements also gave an indication that not more than

2 sequential repeating units of the same monomer are present. This observation implies

that nonstoichiometric feed of the comonomers result in prevalent alternating fashion

also in RAFT copolymerization of styrene with N-phenyl maleimide.

The M n values obtained from MALDI-TOF-MS analyses were compared with the

values calculated from 1H NMR according to the dithioester moiety. By this compar-

ison, rough estimation of end-functionalities was done. 80% dithioester functionality

was calculated for P(SMI)3 and 76% functionality was calculated for P(SMI)4.

ppm (t1)

6.006.507.007.508.008.50ppm (t1)

6.006.507.007.508.008.50

(i)

(ii)

a

b

c

(ii)

(i)

b

c

c

a

Figure 2.22: 1H NMR of P(SMI)3 (ii) and its reduction product after aminol-ysis (i) - (a) ortho protons of thiobenzoate, (b) para proton of thiobenzoate, (c) aromaticgroups of the main chain

Copolymers of styrene with maleic anhydride could be synthesized via RAFT poly-

merization. However, aminolysis reaction in this copolymer is not suitable due to

the high electrophilic nature of the anhydride groups. Maleimides do not react with

57


amines which makes the aminolysis reaction possible for the end-group modification of

maleimide copolymers synthesized via RAFT polymerization.

The procedure for the aminolysis of dithioester moiety into a thiol in PS has been

performed for ω-dithioester-functional P(SMI) as well. The product has been charac-

terized by 1H NMR, and it is observed that the signals that correspond to the aromatic

protons of the dithioester moiety have disappeared. SEC traces showed slight high

molar mass shoulder which implies that there is some disulfide formation. Deconvolu-

tion of the peaks showed that around 8% of the chains are terminated by coupling in

both samples. Figure 2.22 shows 1H NMR characteristic peaks of P(SMI)-RAFT and

P(SMI)-SH. Signals of protons of thiobenzoate group in ortho and para positions have

disappeared in the aminolyzed sample.

2.4 Conclusions

Among all approaches on the way of obtaining well-defined, highly functional high T g

thermoplastic polymers with a thiol moiety, the RAFT polymerization route followed

by aminolysis has been found to be the most effective for the synthesis of ω-thiol-

functional PS. RAFT polymerization followed by the aminolysis has milder reaction

conditions, shorter reaction time and higher end-function purity compared to the S-

alkylation route. ARGET ATRP followed by the azide route and LiALH4 reduction

is the most efficient route for the PS synthesized with 1-PEBr initiator in order to

have the highest functionality and for preventing further potential side reactions in

amine-anhydride coupling reactions. The staudinger reaction should be preferred for

the ω-amine-functional P(SMI) synthesis due to the side reaction of LiAlH4 with the

imide carbonyls. These well-defined high functional polymer are to be used as building

blocks for the further polymer-polymer coupling reactions on the way of synthesizing

TPEs with graft morphology.

58

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60

3

Thermoplastic Elastomers via

Amine-Anhydride Coupling

Abstract

Conversion efficiency is the most important factor in polymer-polymer coupling re-

actions. Ill-defined products are prohibited by high conversions even in stoichiometric

amount of the building blocks. Amine-anhydride coupling reaction between PS and

EPM was found to be highly efficient and robust at a wide variety of reaction parame-

ters. In this chapter, the study on amine-anhydride coupling reaction between ω-amine-

functional thermoplastic polymers (PS and P(SMI)) and maleated ethylene-propylene

copolymer (EPM) will be described and grafting yield results will be discussed with

respect to the various reaction parameters.

61

3 Thermoplastic Elastomers via Amine-Anhydride Coupling

3.1 Introduction

One of the synthesis routes of TPEs with graft morphology is the ‘grafting onto’

approach which is grafting a molecule bearing a suitable function onto a pendant-

functional polymer or a functional surface. The ‘Grafting onto’ approach is used for

making copolymers with brush-/comb-like topologies [1], for modification of a polymer

to alter its properties [2] and for surface modification [3]. Click reactions such as Huis-

gen azide-alkyne 1,3-cycloaddition are widely used in grafting onto reactions. Click

reactions are to give high yields in stoichiometric amounts of components, which leads

to well-defined structures in the synthesis of copolymers via polymer-polymer coupling.

Sharpless et al. state that the formation of an intermolecular C-C bond is much tougher

than the formation of heteroatom bonds. Heteroatom connections with spring-loaded

electron-poor sites are ‘the key elements in a fast, process-driven approach to molec-

ular discovery’ [4]. In this respect, reactions involving heteroatoms such as thiol-ene

coupling and amine-anhydride coupling are promising to be used as highly-efficient cou-

pling reactions. Amine-anhydride coupling is the scope of this chapter, while thiol-ene

coupling will be discussed in Chapter 4.

The coupling reaction between an amine and a cyclic anhydride is the most common

technique used for reactive compatibilization of blends in the melt. Amine-anhydride

coupling is known to be fast and able to proceed to complete conversion in a homo-

geneous melt. However, graft copolymer formation was found to be slower than the

formation of a block copolymer, and the rates were affected by thermodynamic inter-

actions of the immiscible polymers [5]. The amine-anhydride reaction is known to be

not diffusion controlled for homogeneous reactions [6], which is potentially promising

for high yields in heterogeneous reactions.

In polymer-polymer coupling reactions in general, physical parameters such as solu-

tion viscosity and miscibility of the polymers are the main factors affecting the coupling

yield. Polymer-polymer coupling reactions require special attention for one of these

physical aspects, which is miscibility or entropy of mixing. No matter how efficient

and robust a coupling reaction is, miscibility of the components plays the main role in

polymer-polymer coupling. Mixtures of incompatible polymers exhibit phase separa-

tion. Phase separation occurs in order to minimize the contact area between the two

components. Miscibility of two components can be predicted from the Gibbs energy of

62

3.1 Introduction

mixing (∆Gmix), which is formulated by the Equation 3.1:

∆Gmix = ∆Hmix − T∆Smix (3.1)

where ∆Hmix and ∆Smix are enthalpy and entropy of mixing, respectively at a

temperature T. If only ∆Gmix<0 and second derivative of ∆Gmix value with respect

to the composition is positive, the mixing is favorable. To achieve ∆Gmix<0, entropic

term should be larger than the enthalpic term. The most relevant explanation of the

entropy and the enthalpy of polymer mixtures is expressed in the Flory-Huggins theory.

Flory-Huggins equation can be expressed as shown in equation 3.2 [7]:

∆GmixRT

=φ1

r1lnφ1 +

φ2

r2lnφ2 + χFHφ1φ2 (3.2)

where φ1 and φ2 are the volume fractions and r1 and r2 are the relative molar

volumes of polymer 1 and polymer 2, respectively; where r1 is equal to 1 for a solvent,

χFH is the Flory-Huggins interaction parameter, R is the gas constant and T is the

absolute temperature. The first two terms in the equation are related to the entropy of

mixing and the last element is related to the enthalpy of mixing. The entropic element

of the equation simply states that entropy of mixing decreases with an increase in the

molar mass. In the enthalpic element, the χFH term is a material-specific parameter

which is dependent on temperature and concentration [7]. In the melt, PB is immiscible

with PS or P(SMI). The use of a common solvent overcomes this phase separation

barrier, by adding a third component in the Flory-Huggins theory, with r1 = 1, which

dramatically increases the value of the entropic element and shifts the Gibbs free energy

to a negative value.

Swelling and solubility properties of the components is another factor affecting the

miscibility. The dissolution process of a polymer is described by two steps. The first

step is swelling, where the solvent or any low molar mass compound diffuses through the

chains and forms a polymer gel. If the amount of solvent is large enough, the swelling

continues and at a point, solvent molecules surround the whole chain and disentangle-

ment starts. The polymer dissolves completely when there are no more entanglements

among the chains. Molar mass of a polymer has an effect on the dissolution process

of the polymer in a medium. A higher molar mass means a larger number of entan-

glements per chain and consequently more solvent is needed to dissolve polymers with

63


higher molar masses. The entanglement molar mass (M e), which is the molar mass

between the entanglement points, is an intrinsic property of a polymer. EPM could

be considered to have an approximate entanglement molar mass of 3000 which is the

average between the M e of polypropylene, which is 5000 and polyethylene, which is

1000 [8]. Polymers with low entanglement molar mass require a larger amount of sol-

vent to be fully dissolved. Interactions of amine and anhydride groups may potentially

be affected by the solubility properties of EPM and diffusion phenomena between the

thermoplastic phase and the elastomer phase.

In this chapter, the grafting onto approach was studied within an amine-ω-functional

high T g thermoplastic polymer, namely PS and P(SMI) and anhydride-pendant func-

tional elastomer in terms of amine-anhydride coupling. PS and P(SMI) obtained with

high amine end-functionalities were coupled with EPM elastomer. Molar mass of PS,

molar mass of EPM, weight ratio of the components, reaction concentration, stoichiom-

etry of the functional groups and composition of the grafting polymers were varied.

TPEs obtained were compared in terms of grafting yield and will be compared in terms

of resulting mechanical properties in Chapter 6.


3.2.1 Materials

Toluene (Biosolve, AR), tetrahydrofuran (THF, Biosolve, AR) were used as received,

PS-NH2 and P(SMI)-NH2 were synthesized according to the procedures explained in

Chapter 2. Maleated ethylene-propylene copolymers (EPM) with various molar mass

and maleic anhydride content (see Table 3.4) were donated by LANXESS N.V.

3.2.2 Methods

Compositional characterization of the samples was done by Fourier Transform In-

frared Spectroscopy consisting of a Bio-Rad Excalibur FTS3000MX infrared spectrom-

eter with an ATR diamond unit (Golden Gate). The solid samples were pressed onto

the ATR crystal with the help of the pressure handle, 60 scans were made per spectrum

with a resolution of 4 cm−1.



64



Waters 2487 dual absorbance detector (254 nm was used), a PSS SDV 5 µm guard

column followed by 2 PSS SDV linearXL 5 µm columns (8 mm * 300 mm) in series

at 40 ◦C. Tetrahydrofuran (THF stabilized with BHT, Biosolve) with 1% (v/v) acetic

acid was used as eluent at a flow rate of 1.0 mL/min. The molar masses were calculated

with respect to polystyrene standards (Polymer Laboratories, M p = 580 Da up to M p

= 7.1x106 Da). The samples were dissolved in eluent solution with a concentration of

1 mg/mL and filtered through a 0.2 µm PTFE filter (13 mm, PP housing, Alltech).

3.2.3 Dehydration of Maleic Acid Pendant-functions on EPM

A Schlenk flask was charged with 1 g of EPM (M n: 50 kg/mol, D: 2.25, 2.1% maleic

anhydride (w/w)), heated up to 150 ◦C in an oil bath, kept under high vacuum for 4

hours.

3.2.4 Amine-anhydride Coupling of EPM and PS-NH2

1 g of dehydrated EPM (0.21 mmol anhydride) was dissolved in 20 mL of PS solution

(1 g, 0.13 mmol amine) in dry toluene and stirred overnight at ambient temperature.

The polymer was precipitated in ethanol, filtered and dried under vacuum at 60 ◦C.

3.2.5 Amine-anhydride Coupling of EPM and P(SMI)-NH2

1 g of dehydrated EPM (0.21 mmol anhydride) was dissolved in 20 mL of P(SMI)

solution (1 g, 0.1 mmol amine) in dry THF and stirred overnight at ambient tempera-

ture. The copolymer was precipitated in ethanol, filtered and dried under vacuum at

60 ◦C.

3.2.6 Dehydration of Amic Acid Function into Imide

A Schlenk flask was charged with 2 g of amine-anhydride reaction product, heated

up to 150 ◦C in an oil bath, and kept under high vacuum for 4 hours.

65



3.3.1 Approaches for the Quantitative Analysis of Grafting Efficiency

Amine-anhydride coupling is a fast and robust reaction under dry conditions for low

molar mass compounds. Figure 3.1 shows the steps of the amine-anhydride coupling

reaction between EPM and PS. However, in polymer-polymer coupling reactions, there

are different parameters that can affect the coupling efficiency, namely the reaction

concentration and molar mass of the reacting polymers both of which affect the entropy

of mixing, the intrinsic rate of the coupling reaction, the viscosity of the solution and

therefore the miscibility of the building blocks and the mobility of the functional groups

in the solution.

Figure 3.1: Reaction route from commercial EPM to EPM-g-PS via amine-anhydride coupling - anhydride ring closure (a) followed by the addition of the amineend-functional PS (b) and further ring closure of the amic acid (c)

Grafting yields were calculated from the UV traces of SEC measurements. EPM

elastomer has no UV absorption at 254 nm, where the PS gives absorption. Therefore,

the UV trace of SEC measurements gives a quantitative analysis for grafting yield with

respect to the initial PS amount. Calculations of coupling efficiency with respect to

66


total PS, amine, EPM and anhydride are defined by equations 3.3, 3.4, 3.5, and 3.6,

which are:

CEPS =Ag

Ag +Af(3.3)

CEamine =CEPSf

(3.4)

CEEPM = CEPS ∗ [PS]

Mn(PS)∗ Mn(EPM)

[EPM ](3.5)

CEMAn = CEPS ∗ [PS]

Mn(PS)∗ Mn(MAn)

[MAn](3.6)

where CEPS is the coupling efficiency with respect to total PS amount in the

resultant TPE, CEamine is the coupling efficiency with respect to the amine end-

functionality, CEEPM is the coupling efficiency with respect to the EPM chains, and

CEMAn is the coupling efficiency with respect to the anhydride concentration present in

the solution. Ag is the area of the SEC signal corresponds to the conjugated PS chains,

Af is the area of the SEC signal corresponds to the free PS chains, f is the fraction

of PS chains with a amine functionality, [PS], [amine], [EPM] and [MAn] are the con-

centrations of the PS, amine moiety, EPM and anhydride groups in the corresponding

reactions.

The SEC method is not a sufficient technique to quantify the grafting yield with

respect to elastomer, since the retention times of the grafted and non-grafted elastomer

in RI traces are fairly close, and there is no clear observation of a change in the shape

of the peak. An example of a SEC measurement is shown in Figure 3.2.

Complementary characterization for the modified anhydride units was done by

FTIR. FTIR is a robust method in terms of analyzing the coupling efficiency with

respect to the elastomer. In amine-anhydride coupling, as it is seen in Figure 3.1, the

anhydride ring opens with the nucleophilic attack of the amine and amic acid is formed.

Following ring closure of the amic acid leads to the imide formation.

Infrared absorption frequencies of carboxylic anhydride, amide, acid and imide func-

tional groups are distinguishable in the spectrum. In Table 3.1, assignments of absorp-

tion frequencies of the concerned functional groups are shown.

FTIR measurements were performed by the ATR method. The presence of imide

carbonyl anti-symmetric stretch around 1785 cm−1 supports the SEC data qualitatively.

In Figure 3.3, the formation of an imide is seen while the anhydride units are still present

67


14 16 18 20 22

0.00

0.02

0.04n

orm

aliz

ed

UV

sig

na

l (2

54

nm

)

retention time (min)

C124

PS

EPM

Figure 3.2: UV traces of SEC measurements of reactants and the product ofamine-anhydride coupling - EPM and EPM-g-PS (C124, see Table 3.3) samples areboth measured before the ring closure

Table 3.1: Assignment of the IR absorption frequencies of corresponding groups [9]

Wavenumber(cm−1) Assignment1785 maleic anhydride C=O (anti-symmetric stretch)1860 maleic anhydride C=O (symmetric stretch)1725 maleic acid C=O1705 maleimide C=O (anti-symmetric stretch)1770 maleimide C=O (symmetric stretch)1650 amic acid C=O (amide stretch)1720 amic acid C=O(acid stretch)1540 amide N-H (bending)1370 methyl C-H (symmetric deformation)

which implies that the grafting is not complete. Quantitative analysis of the imidization

reaction by FTIR method was done by normalizing the spectra with respect to the

symmetric deformation of pendant methyl groups on elastomeric main chain which

gives an absorption around 1370 cm−1. Decrease in the area of anhydride carbonyl

anti-symmetric stretch absorption was calculated. This data gives an indication of the

grafting yield with respect to the elastomeric building block.

Both SEC and FTIR are not sufficient to analyze the grafting efficiency quanti-

tatively with respect to the elastomer, since the anhydride functionality is randomly

distributed on the EPM main chain. Quantitative analysis of non-grafted elastomer

needs to be done by a chromatographic technique. Although, the separation of func-

tional and non-functional chains of EPM was successful by the GPEC method [10],

the separation of functional non-grafted EPM chains and grafted EPM chains was not

68


1300 1400 1500 1600 1700 1800

CH2 + CH

3

CH3

aromatic C=Cimide anhydride

wavenumber (cm-1)

EPM-g-MA

EPM-g-MAn

EPM-g-PS

acid

Figure 3.3: Comparison of neat EPM (maleic acid pendant function), EPM-MAn (maleic anhydride pendant function), and EPM-g-PS (PS grafted EPM- The spectra are shifted vertically for clarity, and characteristic peaks are labeled

achieved. Therefore the results will not be discussed here.

3.3.2 Effect of Molar Mass of Building Blocks

3.3.2.1 Molar Mass of the Grafting Chain

PS-NH2 homopolymer has been synthesized in different molar masses for the utiliza-

tion in amine-anhydride coupling reactions. The details of the synthesis were discussed

in Chapter 2. Table 3.2 shows the list of the PS-NH2 samples with characterization

data.

Table 3.2: ω-amine functional PS utilized in amine-anhydride coupling reactions

Sample % f M n D(SEC) (SEC)

PS117 82 2,000 1.26PS123 78 5,800 1.25PS124 75 2,300 1.3PS137A 60 10,000 1.2PS137B 82 10,000 1.4PS148 24 4,800 1.26

Table 3.3 shows a list of coupling reactions between EPM and PS performed by

varying the molar mass of PS, solid content, and weight ratio of the reactants.

69


Table 3.3: A set of PS-EPM coupling reactions at varying reaction parameters

Sample solid content [MAn]/[NH2] EPM/PS M n PS CEamine CEEPM

(g/100 mL solvent) (w/w) (SEC) (%) (%)C101 5 1:1.8 1 2000 69 1200C125 10 1:0.6 1 5800 89 577C128 10 1:0.2 2 10000 90 179C104 20 1:0.3 2 5800 100 326C118 20 1:0.14 2 10000 63 92C105 17 1:0.16 4 5800 93 152C106 16 1:0.3 5 2300 100 343C107 15 1:0.17 9 2300 100 177C108 10 1:0.17 9 2300 87 150C123 13 1:0.07 9 5800 70 50C119 20 1:0.07 4 10000 25 19C122 10 1:0.1 3 10000 50 50C124 13 1:0.8 2 2300 83 709C130 10 1:0.04 9 10000 68 31

Increasing PS molar mass would be expected to result in lower coupling yields un-

der constant solid content and constant weight ratio of PS to EPM. However, variation

in the molar mass of PS while keeping the solid content and weight ratio of the reac-

tants constant, varies the stoichiometric ratio of amine to anhydride functionalities. A

comparison of the samples C125 and C128, where the solution concentration is rela-

tively low diminishing the effect of the viscosity, shows that high molar mass PS and

low molar mass PS possess nearly the same coupling efficiency. This implies that, the

other parameters such as stoichiometry of reactants and solution concentration could

be more significant than the molar mass of the thermoplastic polymer grafting onto the

elastomer.

Figure 3.4 represents the coupling efficiencies of the reactions as a function of EPM

concentration for different PS molar masses. The results imply that increasing the

EPM concentration, decreases the coupling efficiency of high molar mass PS. This is

valid for the PS with 10 kg/mol molar mass, however this was not seen for the PS with

5 kg/mol molar mass. It could be claimed that while the miscibility was sufficient even

in high concentrations of EPM for the 5 kg/mol PS, for the 10 kg/mol PS entropy of

mixing decreases so dramatically that it results in very low coupling efficiency values.

The results were associated with entropy of mixing since a visible phase separation was

observed in coupling reactions done in high concentrations with 10 kg/mol PS. This

phenomena will be discussed in Section 3.3.4.

70


2 4 6 8 10 12 14 16

40

50

60

70

80

90

100

110

CE

am

ine

EPM conc (g/100 mL solvent)

PS 2000

PS 5000

PS 10000

Figure 3.4: Coupling efficiency trends of EPM-PS coupling reactions - CEaminevs. EPM concentration is drawn with respect to the molar mass of PS

3.3.2.2 Molar Mass and Functionality of the Grafted Chain

Five different EPM elastomers were used in the coupling reactions. Table 3.4 shows

the results of PS-EPM coupling reactions with the characteristics of the EPM elas-

tomers that have been used. All reactions are done at a solid content of 10 g/100 mL

solvent.

Table 3.4: EPM-PS coupling with varying EPM molar mass and functionality

Sample [MAn]/[NH2] EPM/PS M n EPM %f CEamine CEEPM

(w/w) (SEC) (EPM) (%) (%)C141A 1:0.06 4 50,000 2.1 79 51C141B 1:0.06 4 50,000 2.2 87 63C141C 1:0.06 4 25,000 2.1 83 28C141D 1:0.12 4 50,000 1.1 50 34C141E 1:0.06 4 60,000 2.2 50 41

No significant difference in coupling efficiency was seen between the batches per-

formed with 50 kg/mol and 25 kg/mol EPM, however EPM with 60 kg/mol molar mass

showed significantly less coupling efficiency than the others, which is expected due to

lower entropy of mixing. The EPM sample with 1.1% anhydride content, which has 50

kg/mol molar mass, showed lower coupling efficiency than those with higher anhydride

71


content. The molar mass of the elastomer could be considered as a factor, due to its

effect on dissolution process. However, the decrease in the density of anhydride groups

also decreases the coupling efficiency. This implies that the diffusivity of PS chains are

more limited in EPM with low anhydride content. This is probably due to the fact

that low anhydride content lowers the ‘compatibilizer’ effect, and also the number of

encounters of the reacting groups.

3.3.3 Effect of the Composition of the Building Blocks

Synthesis of ω-amine functional P(SMI) was performed, of which the details were dis-

cussed in Chapter 2. Table 3.5 shows the reaction parameters compared with coupling

efficiency results of coupling reactions performed between EPM and P(SMI).

Table 3.5: EPM-P(SMI) coupling with varying solid content

Sample solid content [MAn]/[NH2] EPM/P(SMI) M n P(SMI) %f CEamine CEEPM

g/100 mL solvent (w/w) (SEC) (P(SMI)) (%) (%)C301 10 1:0.11 4 6000 56 10 114C302 7 1:0.11 4 6000 56 20 15.6C303 4 1:0.22 2 6000 56 8 33.3C304 7 1:0.22 2 6000 56 6 25C305 10 1:0.22 2 6000 56 6 25

Visible phase separation was observed at 10 % solid content. This observation shows

that the miscibility of P(SMI) with EPM is lower than that of PS with EPM. Dilution

slightly increased the coupling efficiency, however it is far away from a quantitative

yield. Since the reaction mixtures with relatively low concentrations were optically

clear, no dramatic increase in coupling yields suggests that molecular mixing was not

achieved in moderate dilution. In high dilutions, the decreased number of encounters

plays the significant role in low coupling efficiency. Using THF instead of toluene could

have a minor effect from the point of high hygroscopic nature of THF, which introduces

moist to the reaction.

3.3.4 Effect of Stoichiometry of Building Blocks and Reaction Con-

centration

In a common solvent, EPM and PS may be miscible or phase separate at room

temperature depending on the solution concentration and molar mass of polymers. As

the molar mass of the polymer increases, at constant solution concentration, the entropy

72


of mixing decreases. At a certain point, value of entropy of mixing is so low that two

polymers eventually phase separate in a common solvent. This phenomenon is valid

in case of increasing the solution concentration at constant molar mass of polymers.

Table 3.6 shows the list of coupling reactions where the stoichiometry of reactants and

solution concentration was varied.

Table 3.6: Comparative EPM-PS coupling reactions at varying reaction concentrationand stoichiometry of reactants

Sample solid content [MAn]/[NH2] EPM/PS M n PS CEamine CEEPM

(g/100 mL solvent) (w/w) (SEC) (%) (%)C114 13 1:0.20 3.3 5800 83 163C115 6.5 1:0.20 3.3 5800 83 163C116 4.3 1:0.20 3.3 5800 80 158C117 20 1:0.3 1 10000 62 179C118 20 1:0.14 2 10000 63 92C119 20 1:0.07 4 10000 25 19C120 20 1:0.03 9 10000 35 11C128 10 1:0.2 2 10000 90 179C130 10 1:0.04 9 10000 68 31

Elastomers, even in dilute solutions (< 5% solid content) increase the solution

viscosity dramatically, the chains swell and shows gel-like behavior. This viscosity

change plays a physical role in the coupling reactions. Higher viscosity reduces the

mobility of the chains. However, on the other hand, despite a high viscosity, high

concentration of the reaction mixture potentially leads to an increase in the possibility

of encounter of the reacting groups as well.

The samples C119 and C120 showed visible phase separation, while C117 and C118

showed no visible phase separation. This is due to the EPM concentration in the solu-

tion. Above a certain value of EPM concentration, two polymer phases are not miscible

anymore. As expected, the coupling efficiency of the reactions done in heterogeneous

medium are significantly lower than those done in homogeneous medium. While keep-

ing the reactant stoichiometry constant, the solution concentrations were decreased and

quantitative coupling was achieved with 10 kg/mol PS samples. Nevertheless, the effect

of stoichiometry was not observed. A graph of coupling efficiency vs. EPM concen-

tration was plotted with respect to the stoichiometric ratio of the reactant functions

(Figure 3.5), no significant trend is seen.

Further dilution was done (samples C114, C115 and C116) at constant stoichiome-

try of the reactants, and a slight decrease was found in the most dilute solution. This

73


2 4 6 8 10 12 14 16

40

50

60

70

80

90

100

110

CE

am

ine

EPM conc. (g/100 mL solvent)

[MAn]/[NH2]<4

4<[MAn]/[NH2]<7

7<[MAn]/[NH2]

Figure 3.5: Coupling efficiency trends of EPM-PS coupling reactions - CEaminevs. EPM concentration is drawn with respect to the stoichiometry of the reactants

implies that there is an optimum solution concentration for the highest coupling effi-

ciency which was found in the range between 10 and 20 g/100 mL solvent. In these

concentrations, depending on the stoichiometry of the reactants and molar mass of the

polymers as well, quantitative coupling could be achieved.

3.4 Conclusions

Amine-anhydride coupling was found to be a robust reaction for polymer-polymer

couplings with quantitative yields under optimum conditions. The data obtained in this

study showed that as long as PS and EPM is miscible in a common solvent, the amine-

anhydride reaction results in quantitative yields at ambient temperature. Increasing

molar mass of PS decreases the miscibility/diffusion of PS chains into the elastomeric

medium. The main parameter determining the coupling efficiency was found to be the

EPM concentration which directly affects the miscibility of the conjugating polymers

and solution viscosity. However if the molar mass of PS is low enough to allow diffusion

through the elastomeric medium, quantitative coupling is achievable in a wide rage

of solution concentration. Furthermore, overdilution decreases the coupling efficiency

74

3.4 Conclusions

due to the decreasing number of encounters of the reactant functions, which could be

compensated by larger reaction times.

Miscibility of P(SMI) and EPM is lower than that of PS and EPM under the

same conditions. Further dilution of P(SMI)-EPM coupling reactions resulted in higher

coupling efficiencies. The coupling efficiency is limited due to the necessity of high

dilution to overcome the incompatibility of the conjugating polymers.

Despite the fact that the quantitative coupling is achieved in the reactions per-

formed, the amine functionality is not 100% in the starting PS and P(SMI) compounds,

therefore the resultant TPEs still have non-grafted free thermoplastic polymer chains

present in their structure.

75


76

Bibliography

[1] H. Gao and K. Matyjaszewski. Journal of the American Chemical Society,129(20):6633–6639, 2007. 62

[2] T. Chen, G. Kumar, M. T. Harris, P. J. Smith, and G. F. Payne. Biotechnologyand Bioengineering, 70(5):564–573, 2000. 62

[3] F. Bauer, H. Ernst, U. Decker, M. Findeisen, H. Glsel, H. Langguth, E. Hartmann,R. Mehnert, and C. Peuker. Macromolecular Chemistry and Physics, 201(18):2654–2659, 2000. 62

[4] H. C. Kolb, M. G. Finn, and K. B. Sharpless. Angewandte Chemie InternationalEdition, 40(11):2004–2021, 2001. 62

[5] C. V. Macosko, H. K. Jeon, and T. R. Hoye. Progress in Polymer Science,30(89):939 – 947, 2005. 62

[6] C.A. Orr, J.J. Cernohous, P. Guegan, A. Hirao, H.K. Jeon, and C.W. Macosko.Polymer, 42(19):8171 – 8178, 2001. 62

[7] Y. C. Bae, J. J. Shim, D. S. Soane, and J. M. Prausnitz. Journal of AppliedPolymer Science, 47(7):1193–1206, 1993. 63

[8] F. Mighri, M. A. Huneault, A. Ajji, G. H. Ko, and F. Watanabe. Journal ofApplied Polymer Science, 82(9):2113–2127, 2001. 64

[9] C. X. Sun, M. A. J. van der Mee, J. G. P. Goossens, and M. van Duin. Macro-molecules, 39(9):3441–3449, 2006. 68

[10] P.J.C.H. Cools, F. Maesen, B. Klumperman, A.M. van Herk, and A.L. German.Journal of Chromatography A, 736(12):125 – 130, 1996. 68

77

BIBLIOGRAPHY

78

4


Thiol-ene Coupling

Abstract

Efficiency and orthogonality of the chemistry used in polymer-polymer coupling

reactions are the key concepts for synthesizing well-defined macromolecular architec-

tures without purification or post-reaction steps. Radical thiol-ene coupling reaction is

a good candidate for this aim, since this approach is known to be successful in poly-

merization and polymer functionalization applications, and there are few studies on

its efficiency in polymer-polymer coupling reactions. In this chapter, thermoplastic

elastomers with graft topology were synthesized via radical thiol-ene coupling reaction

between 1,2-polybutadiene and ω-thiol-functional PS and P(SMI). Coupling efficiency

results will be presented and discussed with respect to the varied reaction parameters.

79

4 Thermoplastic Elastomers via Thiol-ene Coupling

4.1 Introduction

Radical thiol-ene coupling is the second ’grafting onto’ approach for the synthesis of

TPEs with graft morphology. Thiol-ene coupling was investigated in different aspects

in polymer chemistry such as a polymerization technique for synthesizing copolymers

with different topologies, a ’click’ technique for polymer-polymer coupling and polymer

functionalization. Radical thiol-ene reaction has been found to be orthogonal and

efficient for the polymer functionalization [1], [2], as well as the Michael addition, in

which an activated double bond is coupled with a thiol-bearing molecule in presence of

a phosphine-based catalyst. Michael addition was also reported as an efficient technique

for polymer-polymer couplings [3], which therefore can be considered as a click reaction.

However limitations in efficiency have been reported in the polymer-polymer coupling

reactions via radical thiol-ene coupling [4]. These findings raised the question that

radical thiol-ene reactions could be proposed as a type of ‘click chemistry’ for polymer-

polymer coupling reactions. The mechanism for thiol-ene coupling is illustrated in

Figure 4.1.

R SH R S

R S

R1

SR

R1

SR

R1

R SHS

RR1

R S

ini.

Figure 4.1: Mechanism of radicalic thiol-ene reaction - Initiator is either a thermalinitiator or a photoinitiator

The mechanism of radical thiol-ene reaction is that of a type of a chain transfer

reaction. Ideally, the reaction pathways would consist of only an initiation, one-step

propagation and a chain transfer step which are shown in Figure 4.1 from top to bottom,

respectively. However, homo-propagation and hydrogen abstraction from unsaturated

bonds are also reported [4]. In the ideal mechanism, the key concept is that the free

radical formed abstracts the acidic proton of the thiol and the formed thiyl radical

subsequently reacts with the unsaturated bond. The formed adduct radical abstracts

80

4.1 Introduction

a proton from another thiol, and the formed thiyl radical attacks another unsaturated

bond. This sequence of steps is referred to as propagation. In the presence of a suf-

ficient amount of thiol with respect to the amount of unsaturated bonds, in principle,

it is expected that the free radical formed from the dissociation of the thermal initia-

tor selectively abstracts a hydrogen atom instead of reacting with the double bonds.

However, it turned out that a stoichiometric amount of thiol to alkene does not lead to

quantitative coupling. Only in the case of excess thiol to alkene, quantitative thiol-ene

coupling is observed [4].

One of the main motivations to use radical thiol-ene reaction for the TPE synthesis

was the opportunity to utilize 1,2-polybutadiene (PB) elastomer without prior modifi-

cation step. Michael addition is not an option for this material, since the double bonds

on PB are not adjacent to a electron-withdrawing group. Moreover, radical thiol-ene

coupling, in which no catalyst is required, counts as clean chemistry compared to Huis-

gen azide-alkyne 1,3-cycloaddition and Michael addition. Radical thiol-ene coupling

as a polymer-polymer coupling method has been scarsely reported [5], so that there is

plenty of scope for the exploration of the characteristics of radical thiol-ene chemistry

in macromolecular media.

In polymer-polymer coupling reactions in general, as discussed in the introduction

of Chapter 3, physical parameters such as solution viscosity and miscibility of the

polymers are the main factors affecting the coupling yield. PB is immiscible with PS or

P(SMI). PB has an M e of 2000 which is relatively a low value compared to other types of

polymers [6]. Similar to the concept introduced in Chapter 3, the extent of miscibility

of PB with the thermoplastic polymers in a common solvent, and diffusivity of PS

chains into swollen PB matrix will be the additional factors influencing the coupling

efficiency.

In this chapter, the efficiency of thiol-ene coupling reaction of 1,2-polybutadiene

(PB) with PS-SH and P(SMI)-SH was investigated by varying the molar ratio of thiol

moiety to alkene moiety, molar mass of the grafting and grafted chains, reactant con-

centration, reaction temperature and type of initiator.

81



4.2.1 Materials

Azobisisobutyronitrile (AIBN, Aldrich), 1,1’-Azobis(cyclohexanecarbonitrile) (ACHN,

Aldrich) were recrystallized from methanol, 2,2’-Azobis(2.4-dimethyl valeronitrile) (AMVN,

Wako), PB (Ricon R© 156, 1400 g/mol 66% 1,2-vinyl content), PB (Ricon R© 150, 20,000

g/mol, 75% 1,2-vinyl content), benzyl mercaptane, 1-phenyl ethyl mercaptane (1-

PESH), toluene (Biosolve, AR), 1,4-dioxane (Merck, >99%) were used as received,

thiol-ω-functional PS, and thiol-ω-functional P(SMI) were synthesized as described in

Chapter 2.

4.2.2 Methods

1H NMR analyses were performed on a Mercury 400, CDCl3 was used as a solvent

for all samples. 10-15 mg of sample was dissolved in 0.8 mL of CDCl3.




Waters 2487 dual absorbance detector (320 nm was used), a PSS SDV 5 µm guard

column followed by 2 PSS SDV linearXL 5 µm columns (8 mm * 300 mm) in series

at 40 ◦C. Tetrahydrofuran (THF stabilized with BHT, Biosolve) with 1% (v/v) acetic

acid was used as eluent at a flow rate of 1.0 mL/min. The molar masses were calculated

with respect to polystyrene standards (Polymer Laboratories, M p = 580 Da up to M p

= 7.1x106 Da). The samples were dissolved in eluent solution with a concentration of

1 mg/mL and filtered through a 0.2 µm PTFE filter (13 mm, PP housing, Alltech).

4.2.3 Model Reactions for Thiol-ene Coupling

In a Schlenk flask, PB (0.1 g, 1.85 mmol double bonds) and benzyl thiol (1.15 g, 9.25

mmol) were dissolved in 5 mL of toluene, degassed with nitrogen for 30 minutes, and

heated to 65 ◦C. 0.15 g of AIBN (0.925 mmol) was dissolved in 1 mL of toluene and

degassed separately. The AIBN solution was injected into the polymer solution. The

reaction mixture was stirred for 20 hours at 65 ◦C under nitrogen atmosphere.

82


4.2.4 Thiol-ene Coupling of Vinylic PB and PS-SH

In a Schlenk flask, PB (2 g, 37 mmol double bond) and thiol-ω-functional PS (1.0 g,

0.4 mmol) were dissolved in 20 mL of toluene, degassed with nitrogen for 30 minutes,

and heated up to 65 ◦C. 4.0 mg of AIBN (0.024 mmol) was dissolved in 1 mL of toluene

and degassed separately. AIBN solution was injected into the polymer solution. The

reaction mixture was stirred for 20 hours under nitrogen atmosphere.

4.2.5 Thiol-ene Coupling of Vinylic PB and P(SMI)

In a Schlenk flask, PB (2 g, 37 mmol double bond) and thiol-ω-functional P(SMI) (1.0

g, 0.2 mmol) were dissolved in 20 mL of 1,4-dioxane-toluene mixture (1:2), degassed

with nitrogen for 30 minutes, and heated up to 65 ◦C. 4.0 mg of AIBN (0.024 mmol)

was dissolved in 1 mL of toluene and degassed separately. AIBN solution was injected

into the polymer solution. The reaction mixture was stirred for 20 hours under nitrogen

atmosphere.


4.3.1 Proof of Concept - Model Reactions

Model thiol-ene coupling reactions were carried out in order to investigate the be-

havior of internal and external vinylic double bonds of PB elastomer towards a primary

thiyl radical. The reaction temperature was 65 ◦C, which is the temperature for a 10-

hour half-life time of AIBN in toluene. In the reactions, equimolar amounts of double

bonds to thiol were used and the amount of radical initiator was varied. The amount

of AIBN was varied between 50 mol% and 5 mol% with respect to thiol. Coupling

efficiency was calculated from 1H NMR analysis results.

The model thiol-ene reaction of a low molar mass vinylic PB with benzyl thiol

showed high coupling efficiency for the external double bonds. The effect of AIBN con-

centration was not clearly observed in the 1H NMR spectra, due to the poor integration

of overlapping peaks. The yields of coupling reactions with 50%, 10% and 5% AIBN

concentration were roughly calculated from 1H NMR spectra and it is found that ap-

proximately 90% of the external (pendant) vinyl groups were coupled with thiol, while

internal double bonds were much less reactive. Conversion of internal double bonds was

83


ca. 10%. This model reaction showed that internal bond reactivity towards a primary

thiyl radical is so low that the the extent of reaction of internal double bonds with a

secondary thiyl radical or a secondary thiyl moiety on a PS chain can be considered as

negligible.

The UV absorption of aromatic and aliphatic compounds is significantly different,

benzyl thiol has an absorption under 320 nm wavelength, whereas vinylic PB is not

active. As a consequence, the UV traces of SEC measurements at 320 nm provide a

qualitative result for the model grafting reactions. Figure 4.2 shows comparative RI

and UV 320 nm traces of PB before and after grafting reactions.

8 10 12 14 16 18 20

0.0

0.2

0.4

0.6

0.8

1.0

no

ma

lize

d R

I sig

na

l

retention time

PB-g-BT

PB

12 14 16 18

-0.01

0.00

0.01

0.02

UV

sig

na

l (3

20

nm

)

retention time

PB-g-BT

PB

Figure 4.2: Comparative SEC traces of neat PB and PB-g-BT (benzyl thiolgrafted) - RI trace (left), UV trace (320 nm) (right)

The RI traces shown in Figure 4.2 show a shift in retention time, which corresponds

to a change in the hydrodynamic volume of the material, which is due to a change in

the structure. In the UV traces, the difference between neat PB and the reaction

product after thiol-ene coupling with benzyl thiol clearly shows that the grafting was

successful. However, a high molar mass shoulder which is already present in the neat

PB clearly increased. This implies that some radicals were terminated by combina-

tion. Consequently, the calculation of reaction yield from 1H NMR spectra was slightly

overestimated.

A second set of model reactions with a secondary thiol was performed, which was

expected to give more insight in the coupling efficiency of ω-thiol-functional PS. In these

model reactions, 1-PESH and high molar mass PB were used. 1H NMR data indicated

that the external double bonds were not totally converted in the reactions where an

equimolar ratio of thiol to ene was used. This result, when compared to the first

84


set of model coupling reactions, shows that a secondary thiyl radical is significantly

less reactive than a primary thiyl. Table 4.1 summarizes the reactions with varied

parameters and extent of conversion values.

Table 4.1: model thiol-ene coupling reactions between vinylic PB and 1-PESH

Sample reactant [vinyl]:[thiol]:[AIBN] T CEvinyl

concentration ( ◦C) (%)(g/100 mL)

A1 2.85 10:10:0.5 65 65A2 3.01 10:5:0.25 65 58B1 2.85 10:10:0.5 65 62B2 2.31 10:5:0.5 65 65C1 3.51 10:10:0.25 65 50C2 2.96 10:10:1 65 75

The extent of modification of external vinyl bonds was found to be roughly 60%.

The calculation was done by assuming that the extent of reaction of internal double

bonds is so little that it can be neglected. The effect of initiator amount was found to

be significant. Increasing the initiator amount, increases the coupling efficiency. Sam-

ple A1 and B1 are a reproduction of the same reaction where 5% error was found in

the calculation of the coupling efficiency values. In the model reactions, no difficul-

ties existed during the filtration of the SEC samples prior to the measurements, and

no shoulders were observed for the samples where an equimolar amount of thiol to

vinyl groups was used. These results lead to a remark that there were no significant

termination reactions for these reactions, which makes the calculations from 1H NMR

spectra reliable. The samples A2 and B2 exhibit high molar mass shoulders in SEC

measurements (Figure 4.3), where the molar concentration of double bonds was in ex-

cess relative to thiols. The shoulder was more significant in sample A2 than it was in

sample B2, where less initiator was employed. This result suggests that a low concen-

tration of thiyl radicals with respect to the vinyl groups increases the homopropagation

of vinyl bonds due to a lack of thiol groups that supply the hydrogen atom for a chain

transfer. The calculation of the coupling efficiency values for samples A2 and B2 are

therefore an overestimation. However, an increase in initiator concentration increases

the extent of the addition of the thiol relative to homopropagation, which was also seen

in the samples where equimolar amounts of reactants were used.

The UV traces and the molar mass distribution results of the reaction products

listed in Table 4.1 compared to neat PB are shown in Figure 4.3. While neat PB

shows no UV activity, all coupled products are UV active. SEC measurements are

85


not absolutely quantitative, since the thiol compound has no distinct peak in the SEC

traces, and no internal standard was used in the reactions. However, normalization

of UV traces relative to RI traces was done and the areas calculated therefrom are in

agreement with the results obtained from 1H NMR analysis for the reactions where no

high molar mass shoulder observed.

12 13 14 15 16 17 18 19

0.0

0.2

0.4

0.6

0.8

1.0

RI sig

na

l

retention time

PB

A1

A2

B1

B2

C1

C2

13 14 15 16 17

-0.0002

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

0.0016

0.0018

No

rma

lize

d U

V s

ign

al (3

20

nm

)

retention time

PB

A1

A2

B1

B2

C1

C2

Figure 4.3: Comparative SEC traces of neat PB and PB-g-PT (1-phenyl ethylthiol grafted) samples - RI trace (left), UV trace (right)

4.3.2 Radical Thiol-ene Coupling in Polymer-polymer Coupling

The radical thiol-ene coupling reaction was investigated in terms of coupling effi-

ciency with respect to a number of parameters, namely molar masses of the building

blocks, stoichiometric ratio of the functional groups, reaction temperature and reac-

tant concentration. A number of reactions were performed in which these parameters

were varied. All thiol-ene coupling reactions were done in toluene and in the presence

of thermal free radical initiators. A molar excess of the double bonds was used in

all reactions, since the weight fraction of the elastomer in the resultant TPE should

exceed that of the hard segment. This fact is a disadvantage according to the model

reactions performed, where low coupling efficiency and PB-PB coupling were observed

in reactions in which less thiol used, and according to the literature mentioned in the

introduction section. However, the coupling efficiencies obtained from model reactions

are high enough to investigate the parameters affecting the coupling efficiency in poly-

meric medium. Additionally, differences in coupling efficiencies will be a parameter in

the discussions on structure-property relations, which will be introduced in Chapter 7.

86


Coupling efficiency results were calculated according to UV traces of SEC measure-

ments at 320 nm. The coupling product has a UV active fraction at lower retention

times which corresponds to PS conjugated to PB. The fraction at the higher retention

times corresponds to the non-conjugated PS. The ratio of the areas of these two peaks

to the total area gives the percent amount of conjugated and non-conjugated PS with

respect to the total PS present in the product. Calculations of coupling efficiency with

respect to total PS, thiol, PB and vinyl are defined by equations 4.1, 4.2, 4.3, and 4.4,

which are:

CEPS =Ag

Ag +Af(4.1)

CEthiol =CEPSf

(4.2)

CEPB = CEPS ∗ [PS]

Mn(PS)∗ Mn(PB)

[PB](4.3)

CEvinyl = CEPS ∗ [PS]

Mn(PS)∗ Mn(vinyl)

[vinyl](4.4)

where CEPS is the coupling efficiency with respect to total PS amount in the re-

sultant TPE, CEthiol is the coupling efficiency with respect to the thiol functionality,

CEPB is the coupling efficiency with respect to the PB chains, and CEvinyl is the cou-

pling efficiency with respect to the vinyl concentration present in the solution. Ag is

the area of the SEC signal corresponds to the grafted PS chains, Af is the area of the

SEC signal corresponds to the free PS chains, f is the fraction of PS chains with a

thiol functionality, [PS], [thiol], [PB] and [vinyl] are the concentrations of the PS, thiol

moiety, PB and vinyl groups in the corresponding reactions.

PS-SH homopolymer with different molar masses have been synthesized for uti-

lization in thiol-ene coupling reactions. The details of the synthesis were discussed

in Chapter 2. Table 4.2 shows the list of the PS-SH samples synthesized via RAFT

polymerization followed by aminolysis and were used in thiol-ene coupling reactions.

Maximum coupling efficiency achieved in all thiol-ene coupling reactions was around

60% with respect to total PS present in the product. This value is also in agreement

with the model reaction results.

87


Table 4.2: ω-thiol functional PS utilized in thiol-ene coupling reactions

Sample % f M n D(1H NMR) (SEC) (SEC)

PS125-1 60 7,500 1.28PS125-3 51 2,500 1.2PS136 75 14,000 1.33PS146-1 61 1,600 1.13PS146-2 78 3,400 1.16PS146-3 69 7,000 1.21

4.3.3 Effect of Molar Mass of Building Blocks

4.3.3.1 Molar Mass of the Grafting Chain

Table 4.3 shows the reactions performed between vinylic PB and ω-thiol-functional

PS where the molar mass of PS was varied. PB with a molar mass of 20 kg/mol was

used in all reactions. The coupling efficiency values were calculated with respect to the

thiol amount and number of PB chains.

Table 4.3: PB-PS coupling reactions by varying the molar mass of PS

Run solid content [DB]:[thiol]:[ini] PB/PS (w/w) T M n (PS) CEthiol CEPB

g/100 mL solvent ( ◦C) (%) (%)112 8.5 370:2.0:0.2 2 65 2,500 63 128113 8.5 370:0.8:0.06 2 65 7,500 37 30141 10 370:0.54:0.04 2 65 14,000 35 19150A 11 370:0.43:0.03 2.5 65 14,000 78 33150D 11 370:1.6:0.16 2.5 65 2,500 59 96150B 17 370:1.8:0.12 0.6 65 14,000 51 93150G 16 370:5.8:0.57 0.7 65 2,500 35 206151B 10 370:2.0:0.16 4 65 1,600 38 72151E 10 370:1.15:0.07 4 65 3,400 39 43142 10 370:0.27:0.02 4 65 14,000 33 9

According to the coupling efficiency results of the reaction sets, no distinct trend was

observed with respect to the molar mass of the polymer. First of all, keeping the weight

ratio of the reacting polymers constant, while varying the molar mass of PS, changes

the stoichiometric ratio of thiol to double bond. This has a tremendous influence on

the conversion of the second order thiol-ene coupling reaction [7]. If the stoichiometric

ratio of thiol to double bond would be kept constant, while varying the molar mass of

PS, weight ratio of reacting polymers would be affected, which influences the solution

viscosity and therefore the miscibility and the mobility of the components. Secondly,

the PS samples synthesized for coupling reactions have different different degrees of

chain-end functionality. Non-functional chains blur the correlation between the molar

mass and the coupling efficiency. Variation in the degree of chain-end functionality

88


also changes the ratio of thiol functionality to the initiator used. Model reactions

show that the initiator concentration is one of the main factors affecting the coupling

efficiency. Secondly, the molar mass of PS does not affect the viscosity of the reaction

mixture in a significant way. The viscosity of the solution is mainly determined by

the concentration of PB. As long as the components are miscible (no visible phase

separation), the molar mass range of PS used can be concluded to have no significant

effect on coupling efficiency, compared to stoichiometric ratio of thiol to double bonds

and compared to the initiator concentration.

4.3.3.2 Molar Mass of the Grafted Chain

The molar mass of the elastomer becomes the main parameter determining the vis-

cosity of the solution at constant values of the solid content. A high viscosity results

in a low mobility of the chains, which actually means that the frequency of encounters

of the functional groups decreases with increasing viscosity. However, if the viscosity

was kept constant by dilution, the frequency of encounters would decrease due to the

space occupied by solvent molecules. In the reactions performed in this study, the solid

content was kept constant in order to observe the diffusivity and miscibility behavior of

the conjugating chains. Two different molar masses of PB were investigated. Table 4.4

shows the reactions performed by varying the molar mass of PB, with reaction param-

eters and coupling efficiencies calculated according to total PS amount and external

vinylic bonds of PB.

Table 4.4: PB-PS coupling reactions by varying the Mwt of PB

Sample solid content [DB]:[thiol]:[AIBN] PB/PS (w/w) T M n (PS) M n (PB) CEPS CEvinyl

g/100 mL solvent ( ◦C) (%) (%)111 15 370:2.0:0.2 2 65 2,500 1,400 35 0.58112 8.5 370:2.0:0.2 2 65 2,500 20,000 32 0.45211A 8.5 370:2.3:0.15 2 65 3,400 1,400 27 0.32212A 15 370:2.3:0.15 2 65 3,400 20,000 43 0.45211B 10 370:2.3:0.15 2 65 3,400 1,400 21 0.26212B 10 370:2.3:0.15 2 65 3,400 20,000 31 0.33

Model reactions showed that a secondary thiol is almost non-reactive towards an

internal double bond. The PB samples used in this study have different molar fractions

of vinylic bonds. The highest extent of addition is observed in sample 111, where the

lowest molar mass components mixed at the highest concentration. However, the next

highest addition yields are seen in 112 and 212B in which higher molar mass PB is

89


used. This result is not in agreement with the polymer mixing theory, and when the

samples 211B and 212B are compared, higher molar mass PB is observed to show higher

coupling efficiency. This could be due to the overdilution of the low molar mass PB

and PS mixtures. Molecular mixing is enhanced by dilution, however, it decreases the

number of encounters of the thiyl radicals and and the vinyl groups that are already

at a lower concentration in low molar mass PB.

4.3.4 Effect of Stoichiometry of Building Blocks and Reaction Con-

centration

In this study, the stoichiometry of the building blocks was varied, while the concen-

tration of PB was kept between 6-8 g per 100 mL solvent to be able to allow the PS

chains in each batch to diffuse under equal conditions. Thus, the effect of thiol/ene

stoichiometry could be seen. PB with a molar mass of 20 kg/mol was used, and the

reaction temperature was 65 ◦C in all reactions.

Table 4.5: PB-PS coupling reactions at varying stoichiometry of the building blocks

Sample solid content [vinyl]:[thiol]:[AIBN] PB/PS (w/w) M n (PS) CEPS CEPB

g/100 mL solvent (%) (%)140 10 139:0.66:0.04 1 14,000 48 69141 10 180:0.47:0.03 2 14,000 26 19142 10 222:0.27:0.02 4 14,000 25 9150A 11 370:0.43:0.03 2.5 14,000 59 33150B 17 370:1.8:0.12 0.6 14,000 38 93150C 9 370:0.36:0.04 11 2,500 34 25150D 11 370:1.6:0.16 2.5 2,500 30 96150E 13 370:2.9:0.29 1.4 2,500 26 149150G 16 370:5.8:0.57 0.7 2,500 18 206150J 14 370:1.8:0.12 0.6 14,000 40 95

The first three entries in Table 4.5 were performed at a constant solid content.

An increase in the PB/PS weight ratio leads to a decrease in the coupling efficiency.

This is due to a decrease in the amount of solvent, which decreases the miscibility of

the components and immobilizes the chains. To distinguish between the parameters

solid content and PB concentration, the reactions with the code 150 in Table 4.5 were

performed. Figure 4.4 shows the comparative SEC traces of the coupling products of

the reactions 150C, D, E and G.

The graph shown in Figure 4.5 summarizes the trend of coupling efficiency with

respect to the solid content, stoichiometry of building blocks and PB concentration

of the reactions 150C, D, E, G. Coupling efficiency decreases with increasing PS/PB

90


14 16 18 20 22

0.0

0.5

1.0

no

rma

lize

d U

V s

ign

al (3

20

nm

)

retention time

PB

C150C

C150D

C150E

C150G

PS

Figure 4.4: UV traces of SEC measurements - Comparison of neat PB, PS andcoupling products of the reactions listed in Table 4.5

weight ratio and with increasing solid content. Although, the concentration of PB

decreases from 8 to 6.5, the efficiency of diffusion of PS into PB also decreases due to

the more concentrated reaction medium.

A comparative graph of the reactions 150A, B and J is shown in Figure 4.6. The

trend observed in this set of reactions is in agreement with the trend that was observed

in the previously mentioned reaction set. The coupling efficiency is mainly dependent

on the solid content, if the stoichiometry of functional groups is kept constant.

4.3.5 Composition of Building Blocks, Effects of Two-solvent System

The main motivation to use P(SMI) as the grafting polymer is to improve the thermal

properties of the resultant TPE, thanks to the high T g of P(SMI) which is around

180 ◦C for the fully alternating constitution [8]. Table 4.6 shows the characteristics of

P(SMI) copolymers used in the coupling reactions.

Table 4.6: ω-thiol functional P(SMI) utilized in thiol-ene coupling reactions

Sample functionality (%) M n (SEC) DP(SMI)3 75 5000 1.25P(SMI)4 70 9500 1.3

Toluene was not used as a solvent in these coupling reactions since P(SMI) does not

dissolve in toluene. Instead, the reactions are performed in toluene-dioxane mixtures.

91


c

d

e

g0

5

10

15

20

25

30

35

PB/PS

solid cont.

PB / tol

CE

Figure 4.5: Coupling efficiency trends of reactions 150C, D, E, G - CEPS resultsare plotted in comparison with the reaction parameters, values are normalized for betterdiscrimination

a

b

j0

10

20

30

40

50

60

PS / PB

PB / tol

solid cont.

CE

Figure 4.6: Coupling efficiency trends of reactions 150A, B, J - CEPS resultsare plotted in comparison with the reaction parameters, values are normalized for betterdiscrimination

92


The solubility of PB in 1,4-dioxane is lower than that in toluene [9]. Using a mixture

of two miscible solvents each dissolving one of the components better is a physical

factor affecting the coupling efficiency of the reactants. Table 4.7 shows the reaction

parameter and calculated coupling efficiencies of the PB-P(SMI) coupling reactions, all

reaction were performed at 65 ◦C and 20 kg/mol PB was used.

Table 4.7: PB-P(SMI) coupling reactions

Sample solid content [vinyl]:[thiol]:[AIBN] PB/P(SMI) M n toluene/dioxane CEP (SMI) CEPB

g/100 mL solvent (w/w) (P(SMI)) (v/v) (%) (%)201 6.6 185:2.00:0.1 1 5,000 2 16 64202 6.6 185:1.08:0.05 2 5,000 2 17 34203 6.6 185:0.5:0.025 4 5,000 2 22 22204 10 185:1.05:0.05 1 9,500 1 3 6205 10 185:0.5:0.025 2 9,500 2 8 8.5206 10 185:0.25:0.013 4 9,500 4 18 9.5

All entries in Table 4.7 show an opposite trend compared to the trend of the reaction

set performed with PS in which the stoichiometry was investigated as a parameter.

This opposite behavior cannot be attributed to compositional difference of P(SMI),

since P(SMI) is also immiscible with PB in the melt. Therefore, instead of an increase,

a decrease would have been expected for the same conditions. However, the reactions

were performed in different ratios of 1,4-dioxane-toluene mixtures, differently from the

batches with PS. 1,4-dioxane and toluene are miscible. All batches were optically clear

during preparation and throughout the reaction, which is an indication that there is

no phase separation between the polymer solutions, and P(SMI) does not precipitate

due to presence of toluene. The first three reactions were done in 2:1 toluene-dioxane

mixture. In the last three reactions, the volume ratio of toluene to 1,4-dioxane was

adjusted according to weight ratio of PB and P(SMI). Figure 4.7 shows the coupling

efficiency trends with respect to the reaction parameters.

First of all, due to the higher solid content in the second set of the reactions, the

coupling efficiency values are relatively lower. The increase in the coupling efficiency

is more significant in the second set of the reactions. This trend indicates that an

increase in the fraction of toluene, does not negatively affect the diffusivity of P(SMI)

chains into the PB phase. Oppositely, a higher amount of toluene swells PB to a larger

extent that miscibility of the polymer solutions is enhanced. Using two-miscible-solvent

system in general appears to be enhancing the miscibility of the polymer solutions. In

other words, the swelling of the elastomer is somewhat limited by using 1,4-dioxane

93


R201

R202

R203

R204

R205

R206

0

5

10

15

20

tol / diox

PB / P(SMI)PB / tol

P(SMI) / dioxCE

Figure 4.7: Coupling efficiency trends of reactions 201-206 - CEPS results areplotted in comparison with the reaction parameters, values are normalized for better dis-crimination

94


additionally which is a good solvent for P(SMI), where the mobility of PS gets enhanced

due to the higher amount of solvent incorporated with P(SMI) rather than PB. This

could result in such a mixture of somewhat multiple semi-phases that the P(SMI)

solution in 1,4-dioxane is in a dynamic equilibrium with the PB solution in toluene.

Decreasing the P(SMI) concentration while keeping the solvent ratio constant, allows

the dioxane to be incorporated more with PB, which explains why not a decrease but

an increase was observed in the first set. However, this effect appears to be not as

strong as the effect of increase in the extent of swelling of PB, which is indicated by

the dramatic change of coupling efficiency in the second set of the reactions.

4.3.6 Effect of Reaction Temperature and Initiator Activity

One of the side reactions in thiol-ene coupling is homopropagation of the unsaturated

bonds, which is initiated by the addition of the free radical formed by the dissociation of

the initiator. This is due to the preference of the initiator-derived radical which attacks

to a double bond instead of abstracting a hydrogen atom from a thiol. Essentially,

if thiol is not in excess, addition of the initiator-derived radical to a double bond

is a significant side reaction in polymer-polymer coupling. Therefore, the reaction

temperature or type of the thermal initiator would play a role in the selectivity between

the two reactions. In this respect, a set of reactions was designed in order to investigate

various azo-initiators at various temperatures. Table 4.8 summarizes the parameters

and coupling efficiency results of the reactions performed.

Table 4.8: Thiol-ene coupling of PB and PS with different thermal initiators and tem-peratures

Run solid content [vinyl]:[thiol]:[ini] Initiator PB/PS (w/w) T t M n (PS) CEPS CEPB

g/100 mL solvent ( ◦C) (h) (%) (%)151A 10 55:0.38:0.03 ACHN 4 88 24 1,600 56 175151B 10 55:0.38:0.03 AIBN 4 65 24 1,600 23 72151C 10 55:0.38:0.03 AMVN 4 51 24 1,600 30 94151D 10 55:0.23:0.015 ACHN 4 88 24 3,400 56 83151E 10 55:0.23:0.015 AIBN 4 65 24 3,400 29 43151G 10 55:0.23:0.015 ADVN 4 51 24 3,400 45 66151H 8 55:0.10:0.007 ACHN 4 88 24 7,000 55 39151J 8 55:0.10:0.007 AIBN 4 65 24 7,000 40 29151K 8 55:0.10:0.007 AMVN 4 51 24 7,000 43 31152A 8 55:0.23:0.015 ACHN 4 65 96 3,400 17 25152B 8 55:0.23:0.015 AIBN 4 65 24 3,400 40 59152C 8 55:0.23:0.015 AMVN 4 65 5 3,400 24 36

All three azo-initiators utilized in this study possess a nitrile moiety. The nitrile

95


group helps to stabilize the radical formed. Besides the stability and reaction preference

of the initiator-derived radical, reaction temperature plays a role in the side reactions.

Thioether adduct radicals have a choice to homopropagate, abstract a hydrogen atom

from another thiol or terminate by coupling with another radical group. Also in this

case, the probability of each of these events is also affected by the reaction temperature.

Highest coupling efficiency values were observed in the reactions done with ACHN

at 88 ◦C, the 10-hour half-life temperature of ACHN. This result is rather due to the

effect of the temperature on the mobility and therefore the miscibility of the polymer

chains than the activity of the initiator radical. Interestingly, reactions performed in the

presence of AMVN at 51 ◦C (10-hour half-life temperature of AMVN) showed higher

coupling efficiency than the reactions performed with AIBN at 65 ◦C. This is believed

to be due to the different structure of AMVN, which forms more stable radical than

AIBN [10]. A more stable radical, which is present in the medium containing the thiol

in minority and double bonds in majority, has a higher chance to abstract a hydrogen

from thiol which is the preferred path in ideal thiol-ene coupling reactions.

12 14 16 18 20 22 24

0.0

0.2

0.4

0.6

0.8

1.0

no

rma

lize

d R

I


C152A

C152B

C152C

Figure 4.8: Comparative SEC traces of PB-PS coupling reactions - at 65 ◦C withdifferent types of initiator

The prevalance of the initiator-derived radical could be followed by performing the

reactions at the same temperature. The runs listed as 152A, 152B and 152C in table

4.8 are the reactions done at the same temperature with different initiators. Reactions

were followed by SEC measurements. Highest coupling efficiency value was observed

96

4.4 Conclusions

in the reaction performed in the presence of AIBN and at 65 ◦C, which is the 10 hour-

half-life temperature of the initiator. Neither of the ACHN or AMVN achieved that

extent of coupling. This means that continuous radical formation with a certain rate is

necessary for achieving high efficiencies in thiol-ene coupling. However, the shape of the

peaks corresponds to the coupled products (Figure 4.8) are the same, indicating that

there is no difference in the selectivity between an addition and hydrogen abstraction

reaction.

4.4 Conclusions

Model reactions between a low molar mass secondary thiol and PB elastomer showed

that coupling is not complete due to the fact that a secondary thiyl radical is not

as reactive as a primary thiyl towards unsaturated bonds. In the presence of excess

double bonds relative to thiol functionalities, homopropagation or termination by the

combination of two propagating PB chains is observed as a side reaction.

As expected, in polymer-polymer coupling reactions, the coupling efficiency value

obtained did not exceed the coupling efficiency obtained in the model reactions. Among

the parameters varied, solid content and reaction temperature were found to be the most

dominant factors affecting the coupling efficiency. Molar mass of the reactants implied

to affect the coupling efficiency, but it was not clearly observed. The variations in the

molar mass of the components changed the other parameters such as the stoichiometry

of the reactant groups and the solution viscosity, which blur the correlation between

the molar mass and the coupling efficiency.

The reactions that were carried out in a binary solvent mixture showed totally dif-

ferent characteristics when compared to the reactions done in a single solvent. The

mutual mixing behavior of two solvents, and solubility properties of the polymer com-

ponents in these solvents resulted in a opposite trend in terms of coupling efficiency to

that was observed in single-solvent system.

Increase in temperature enhances the solubility and the miscibility of the compo-

nents, but type of the initiator was also found to be significant. No difference was

observed in the preference of the initiator-derived radical between a hydrogen abstrac-

tion and addition reaction. However, the activity of AMVN was found to be higher

than that of AIBN at their own 10-hour half-life temperatures. The structure of the

97


initiator seems to affect the coupling efficiency, thus AIBN is suspected to be the most

suitable radical source for the thiol-ene coupling reactions.

98

Bibliography

[1] C. E. Hoyle and C. N. Bowman. Angewandte Chemie International Edition,49(9):1540–1573, 2010. 80

[2] A. Dondoni. Angewandte Chemie International Edition, 47(47):8995–8997, 2008.80

[3] G. Mantovani, F. Lecolley, L. Tao, D. M. Haddleton, J. Clerx, J. L. M. Cornelissen,and K. Velonia. Journal of the American Chemical Society, 127(9):2966–2973,2005. 80

[4] S. P. S. Koo, M. M. Stamenovic, R. A. Prasath, A. J. Inglis, F. E. Du Prez,C. Barner-Kowollik, W. Van Camp, and T. Junkers. Journal of Polymer SciencePart A: Polymer Chemistry, 48(8):1699–1713, 2010. 80, 81

[5] B. S. Sumerlin and A. P. Vogt. Macromolecules, 43(1):1–13, 2010. 81

[6] D. R. Daniels, T. C. B. McLeish, B. J. Crosby, R. N. Young, and C. M. Fernyhough.Macromolecules, 34(20):7025–7033, 2001. 81

[7] B. Chiou and S. A. Khan. Macromolecules, 30(23):7322–7328, 1997. 88

[8] G. Liu, X. Li, L. Zhang, X. Qu, P. Liu, L. Yang, and J. Gao. Journal of AppliedPolymer Science, 83(2):417–422, 2002. 91

[9] R.G. Makitra, E.A. Zaglad’ko, A.A. Turovskii, and G.E. Zaikov. Russian Journalof Applied Chemistry, 77:323–326, 2004. 93

[10] S. J. Blanksby and G. B. Ellison. Accounts of Chemical Research, 36(4):255–263,2003. 96

99

BIBLIOGRAPHY

100

5


Nitroxide Mediated Graft

Polymerization

Abstract

The ‘grafting from’ technique is used as an alternative to ‘grafting onto’, since it

has some advantages compared to ‘grafting onto’ technique in terms of compatibility

of the reactants and grafting efficiency. In this last synthesis chapter, the ‘grafting

from’ approach was investigated in terms of nitroxide mediated graft polymerization

of PS from an elastomeric macroinitiator. By this technique, it is observed that the

grafting density and the molar mass of the grafts can be tuned in a more controlled

way, resulting in materials with well-defined structure.

101

5 Thermoplastic Elastomers via Nitroxide Mediated Graft Polymerization

5.1 Introduction

The second approach investigated in the synthesis of graft TPEs is the ‘grafting

from’ method. In this approach, the grafted chains are formed by polymerization from

the pendant functions of the main chain. In literature, the ‘grafting from’ technique

is used in many applications such as modification of surfaces [1], tuning the proper-

ties of proteins [2], and building complex macromolecular architectures [3], [4]. The

‘grafting from’ technique is also used as an alternative to the ‘grafting onto’ tech-

nique, since it does not suffer from the diffusion problems and low yields of polymer-

substrate/polymer-polymer coupling reactions [5].

Graft polymerization of a monomer from a polymer can simply be done by free

radical polymerization of a monomer in a medium where a polymer is present bearing

unsaturated groups as pendant functions or on the main chain. However, the resultant

material is a mixture of grafted polymer and free homopolymer of the monomer. The

resulting mixture cannot be counted as a well-defined structure. In order to synthesize

well defined copolymers via the ‘grafting from’ approach, a living/controlled polymer-

ization technique is required. CRP methods provide functional graft chain-ends, which

can be further chain-extended to obtain grafted block copolymers. Anionic polymer-

ization, ATRP and NMP work with a hetero-functional initiator, in which the leaving

group of the initiator participates in the ‘end-capping’ process. However, RAFT poly-

merization works with a normal radical initiator, and a highly reactive chain transfer

agent (CTA) which initiates the largest fraction of all polymer chains. This mechanism

of RAFT polymerization limits the potential of this technique to be used as a ‘graft-

ing from’ approach, due to the inevitable formation of free homopolymers. However,

RAFT polymerization finds applications as a ‘grafting from’ technique [2], [5]. ATRP

is a common technique used for the ‘grafting from’ approach. The advantage of ATRP

compared to the other CRP techniques is that the initiation takes place instantly which

allows all the grafting chains to grow simultaneously in the early stages of propaga-

tion. This feature results in denser grafts especially for surface applications where the

hindrance plays an important role. However, the presence of metal complexes leads to

some limitations particularly in bio-related applications.

The third CRP alternative, NMP, has a much simpler formulation than ATRP or

RAFT polymerization. The hetero-functional initiator, alkoxyamine, thermally disso-

102

5.1 Introduction

ciates and the cleaved persistent radical (nitroxide) works as an ’end-capping agent’.

Figure 5.1 shows the mechanism of NMP initiated with a hetero-functional initiator.

Figure 5.1: Mechanism of NMP - (a) dissociation of alkoxyamine, (b) initiation, (c)deactivation in main equilibrium, (d) activation in main equilibrium, (e) propagation

NMP could also be employed with just a nitroxide radical with conventional free

radical initiators, instead of an alkoxyamine. However, hetero-functional alkoxyamine

initiators have better control over molar mass and dispersity than the stable radical-

free radical initiator combination [6]. Additional nitroxide radical is also used together

with the alkoxyamine to have a better control on molecular weight and dispersity in

case of fast polymerizing monomers (e.g. acrylates), or to maximize the polymerization

rate by increasing the reaction temperature. [7].

Use of NMP as a ‘grafting from’ technique in the synthesis of TPEs requires end-

group modification, due to the thermal instability of the alkoxyamine moiety. The end-

functionalization of polymers synthesized via NMP is carried out in order to introduce

new functional end-groups and improving the thermal stability [8]. In this study, it was

desired to have hydrogen terminated chains to prevent any possible reactions during

melt processing. Thiols could be used for the substitution of alkoxyamine group by a

hydrogen. The reaction is illustrated in Figure 5.2. Thiols work as a chain transfer

agent in radical polymerizations, while terminating the growing chain with a hydrogen,

initiates other chains by addition to the double bond [9].

TPE with a graft topology was achieved by grafting an amine functional NMP

initiator onto the EPM (amine-anhydride coupling) followed by graft polymerization of

styrene from the macroinitiator. The amine-functional NMP initiator was synthesized

103


Figure 5.2: Modification of alkoxyamine moiety - Substitution of alkoxyamine witha labile hydrogen of thiol via a radical mechanism

by modification of the carboxylic acid group on the commercial NMP initiator MAMA

SG-1 (BlocBuilder R©).


5.2.1 Materials

Styrene (Aldrich, >99%) was vacuum distilled and stored under argon, 2-methyl-

2-[N-tert-butyl-N-(1-diethoxyphosphoryl-2,2-dimethyl propyl)aminoxy] propanoic acid

(MAMA SG-1, BlocBuilder R©, Arkema), n-hydroxysuccinimide (NHS, Aldrich, 98%),

N-N’dicyclohexylcarbodiimide (DCC, Fluka, 98%), 1-dodecanethiol (Aldrich, 98%),

EPM (Lanxess, 50 kg/mol, 2.1% maleic anhydride (w/w)), tetrahydrofuran (THF,

Biosolve, AR) pentane (Biosolve, AR) dichloromethane (Biosolve, AR), diaminoethane

(Sigma-Aldrich, >99%) acetone (Biosolve, AR) anisole (Aldrich, 99%), toluene (Bio-

solve, AR) were used as received.

5.2.2 Methods

Monomer conversion in the polymerization reactions was determined by a GC450

gas chromatograph (Varian) equipped with a CP-Wax 52CB capillary column (length:

25 m; diameter: 0.4 cm) and with a glass PEG pre-column. Injection temperature was

250 ◦C, and detector temperature was 300 ◦C. Analyses were carried out according to

the following temperature profile: 60 ◦C for 1 min, from 60 ◦C to 100 ◦C with 10 ◦C/min

rate, from 100 ◦C to 210 ◦C with 20 ◦C/min rate, 210 ◦C for 1 min.

1H NMR analyses were performed on a Mercury 400, CDCl3 was used as a solvent

for all samples. 10-15 mg of sample was dissolved in 0.8 mL of CDCl3.

Compositional characterization of the samples was done by Fourier Transform In-

frared Spectroscopy consisting of a Bio-Rad Excalibur FTS3000MX infrared spectrom-

eter with an ATR diamond unit (Golden Gate). The solid samples were pressed onto

104


the ATR crystal with the help of the pressure handle, 60 scans were made per spectrum

with a resolution of 4 cm−1.




Waters 2487 dual absorbance detector, a PSS SDV 5 µm guard column followed by 2

PSS SDV linearXL 5 µm columns (8 mm * 300 mm) in series at 40 ◦C. Tetrahydrofuran

(THF stabilized with BHT, Biosolve) with 1% (v/v) acetic acid was used as eluent at a

flow rate of 1.0 mL/min. The molar masses were calculated with respect to polystyrene

standards (Polymer Laboratories, M p = 580 Da up to M p = 7.1x106 Da). The samples

were dissolved in eluent solution with a concentration of 1 mg/mL and filtered through

a 0.2 µm PTFE filter (13 mm, PP housing, Alltech).

5.2.3 Synthesis of Amine-functional NMP Initiator

5.2.3.1 Synthesis of 2-methyl-2-[N-tert-butyl-N-(1-diethoxyphosphoryl-2,2-

dimehtylpropyl)amino]-N-propionylsuccinimide (NPS SG-1)

MAMA SG-1 (4.8 g, 12.6 mmol) and NHS (1.81 g, 17.7 mmol) were dissolved in 20

mL THF. The solution was degassed with Argon for 30 minutes. A degassed solution

of DCC (3 g, 14.5 mmol) in 5 mL THF was added. After stirring for 1.5 hours at

0 ◦C, the precipitated N,N’-dicyclohexylurea (DCU) was removed by filtration. The

filtrate was concentrated under vacuum to one third volume and placed at −20 ◦C.

After 2h, the residual DCU was precipitated and removed by filtration. The filtrate

was concentrated under reduced pressure. The recovered solution was precipitated

in pentane. The obtained precipitate was further washed with water to remove the

remaining NHS. After drying under vacuum at room temperature, a white powder was

recovered. Yield: 56.4% (3.4 g, 7.1 mmol).

5.2.3.2 Synthesis of 2-methyl-2-[N-tert-butyl-N-(1-diethoxyphosphoryl-2,2-

dimethylpropyl)aminoxy]-N-aminoethylpropionamide (NAP SG-1)

NPS SG-1 (3 g, 6.27 mmol) was dissolved in 30 mL dichloromethane. This was added

to a solution of etylenediamine (19.09 g, 317.65 mmol) in 30 mL dichloromethane. After

addition is complete, the reaction mixture was stirred for 5 hours at room temperature.

105


The solution was extracted with water (3x15 mL). Organic layer was concentrated under

vacuum at 20 ◦C, and the product was recovered as oil. Yield: 65% (1.95 g, 4.6 mmol).

5.2.4 NMP of Styrene

In a Schlenk flask, NPS SG-1 (0.05 g, 0.10 mmol) and styrene (5.22 g, 50.2 mmol) were

dissolved in 5 mL toluene, 0.5 mL anisole is added as an internal standard. The solution

was bubbled with argon for 30 minutes and the t0 sample was taken. The solution was

heated to 90 ◦C. Conversion was followed by GC and build up of molecular with SEC.

After reaching a certain conversion, the reaction was quenched and the solution was

precipitated in methanol. Subsequent to the vacuum filtration, the polymer was dried

under vacuum at ambient temperature.

5.2.5 Ex-situ Modification of ω-nitroxide Functionality

Nitroxide bearing PS (0.5 g, 0.08 mmol) and 1-dodecanethiol (30 mg, 0.15 mmol)

were dissolved in 10 mL toluene, heated to 100 ◦C and stirred for 45 minutes. The

product was isolated by precipitation in methanol, vacuum filtered and dried under

vacuum at 40 ◦C.

5.2.6 Synthesis of NMP Macroinitiator

EPM (0.5 g, 1.05x10−4 mol MAn) was heated up to 150 ◦C for 3 hours under high

vacuum in a Schlenk flask. NAP SG-1 (0.44 g, 1.05x10−3 mol amine functionality) was

dissolved in dry toluene (50 mL) was added and the flask was stirred until EPM was

dissolved and for additional 5 hours. The solution was precipitated in 400 mL acetone.

The macroinitiator was collected by vacuum filtration, and dried under vacuum at

ambient temperature.

5.2.7 Graft Polymerization of Styrene from Macroinitiator

The macroinitiator (0.5 g) was dissolved in 10 mL toluene and 1 mL anisole was

added as internal standard. The solution was bubbled with argon for 30 minutes in a

Schlenk flask. Styrene (4.52 g, 43.4 mmol) was added to the solution and the t0 sample

was taken. The solution was heated up to 90 ◦C. Conversion was followed by GC and

build up of molar mass with SEC. After reaching a certain conversion, the reaction was

106


quenched and the solution was precipitated in methanol. After vacuum filtration the

polymer was dried under vacuum at room temperature to remove any volatiles.

5.2.8 In-situ Modification of ω-nitroxide Functionality

During the polymerization procedure explained in Section 5.2.7, 1-dodecanethiol

(0.212 g, 1.05x10−3 mol) is added to the solution and the reaction was stirred at the

same temperature for 45 minutes.


5.3.1 Synthesis of Amine-functional NMP Initiator

MAMA SG-1 has a carboxylic acid group on its initiating side. By the transformation

of the acid group into an amine it will be possible to graft the initiator onto pendant

anhydride functions of EPM elastomer. Transformation of the carboxylic acid into an

amine was done in two steps, first of which was the attachment of succinimide by DCC

coupling to form an activated ester group, and subsequently reacting this succinimide

ester group with excess diamine. The reaction steps of the transformations are shown

in Figure 5.3.

Figure 5.3: Reaction steps of the transformation of MAMA SG-1 to NAP SG-1- First step is DCC coupling and the second step is aminolysis

107


During the attachment of succinimide on to the carboxylic acid, DCU, which forms

as an oxidation product of DCC, precipitates during the reaction and shifts the reaction

equilibrium to the right. The succinimide ester group formed is an activated ester which

is labile for nucleophilic attacks. A large excess of ethylenediamine nucleophilically

substitutes the succinimide group by minimizing the coupling reactions. Figure 5.4

shows comparative 1H NMR spectra of the SG1 derivatives.

ppm (t1)

1.02.03.04.05.06.07.08.0

ppm (t1)

1.02.03.04.05.06.07.08.0

ppm (t1)

1.02.03.04.05.06.07.08.0

a

b

c

d

e

a

a

a

b

b

d

d

c

e

f

g

f

g

h

j

j h

d

c

c

e

e

f

f

b

g

g

a

a

b

b

c

d

c

d

e

e

f

f

Figure 5.4: Comparative 1H NMR spectra of the SG1 derivatives - MAMA SG-1(bottom), NPS SG-1 (middle) and NAP SG-1 (top)

Integration on 1H NMR spectra of the derivatives shows that the isolated products

obtained the desired functionalities quantitatively. In the transformation of NPS SG-

1 into NAP SG-1, the product obtained was not completely isolated from the NHS

formed as a side product. The shift, which is seen at 2.8 ppm in the 1H NMR spectrum

of NAP SG-1 in Figure 5.4, is caused by the methylene protons of NHS. This shift is

seen in spectra of both NPS SG-1 and NAP SG-1, which leads one to suspect whether

the transformation is complete or not. Additionally, the shift of the proton of the

hydroxide group is not visible. However, the integration values of methylene protons

108


adjacent to phosphoryl group and methylene protons adjacent to the formed amide are

in agreement with the fact that succinimide ester groups are quantitatively converted

to amide. On the other hand, the integration values of methylene protons adjacent to

amide, amine and the protons of amine moiety are also in agreement with complete

conversion and selectivity. This fact also eliminates the possibility of coupling of two

SG-1 molecules in case of insufficient amount of diamine.

5.3.2 A pre-study: NMP of Styrene

Homopolymerization of styrene in toluene via NMP was investigated in order to have

an insight in polymerization kinetics depending on the concentration and temperature.

The findings of this study were expected to clarify the conditions to be applied for the

graft polymerization of styrene from EPM-g-SG1 macroinitiator. Table 5.1 summarizes

the reaction conditions and results of the polymerizations performed. MAMA SG-1 and

NPS SG-1 were comparatively used as an initiator in order to investigate the effect of

the structure of initiating moiety on reaction rate and controllability.

Table 5.1: Reaction conditions and results of NMP reactions

Run [Mon]:[Ini] Ini. t(h) T M n DR112 384:1 MAMA SG-1 28 90 7375 1.3R116 400:1 MAMA SG-1 47 90 18521 1.24R119 420:1 MAMA SG-1 27 90 18526 1.2R122 46:1 MAMA SG-1 3.5 90 820 1.05R106 476:1 NPS SG-1 6.5 95 6340 1.23R108 561:1 NPS SG-1 100 90 11038 1.36R110 357:1 NPS SG-1 53 100 26770 1.3R124 51:1 NPS SG-1 4.2 110 1961 1.1

The conversion of polymerization reactions performed with MAMA SG-1 was not

possible to follow with GC due to the dramatically fluctuating concentration values.

This was possibly due to the overlapping peaks of internal standard and dissociation

product of the MAMA SG-1 during GC measurement. However, a reasonable in-

crease in molar mass was observed in SEC measurements. Therefore, instead of the

ln([M]0/[M]t), ln(M n) was followed as a function of time. Polymerization studies of

styrene with MAMA SG-1 showed linear increase of ln(M n) against time. Two ln(M n)

and D vs. time plots of R119 and R122 are shown in Figure 5.5.

Plot of R119 shows a linear growth of ln(M n) against time up to 50% conversion,

roughly. Conversion values were estimated from the comparison of the M n values

109


20 40 60 80 100 120 140 160 180 200 220

1.000

1.025

6.55

6.60

6.65

6.70

6.75

Ð \

\ ln

(M

n)

time (min)

1250 1300 1350 1400 1450 1500 1550 1600 1650

1.1

1.2

9.60

9.65

9.70

9.75

9.80

9.85

9.90

Ð \

\ ln

(M

n)

time (min)

Figure 5.5: D and ln(M n) vs. time plots - R119 (right), R122 (left)

measured by SEC and theoretical M n to be reached at 100% conversion. Dispersity

values are also virtually constant. Plot of R122 gives an idea for the initiation behavior

of the polymerization. Linear growth of M n is observed up to 17% conversion, and

dispersity values remain constant at 1.03.

Polymerizations have also been performed in the presence of NPS SG-1. Conversion

values were successfully measured by GC. The last five entries in the table 5.1 are the

polymerizations done in the presence of NPS SG-1. The GC measurements were found

to be more realistic in the polymerizations performed by the NPS SG-1 than the ones

performed with MAMA SG-1, therefore conversion values were also taken into account

besides the ln(M n) vs. time plots. Figure 5.6 shows M n vs. conversion and ln([M]0

/[M]t) vs. time plots of the reactions performed at different temperatures (table 5.1).

The kinetic plots of the polymerizations show that there is slow initiation. When

the temperature is increased, slow initiation behavior diminishes. R110 gave the best

results in terms of controllability of the reaction, however 50% conversion has been

reached in 50 hours. R124 was found to be much faster, however the rate of initiation

was not compatible with the rate of propagation. Thus, slow initiation behavior was

observed in the kinetic plot of R124. Dispersity values remain constant at the values

entered in Table 5.1.

110


0 1000 2000 3000 4000 5000

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

ln([

M0]/[M

t])

time (min)

R108

0.00 0.05 0.10 0.15 0.20 0.25 0.30

1000

2000

3000

4000

5000

6000

7000

8000

9000

Mn

conversion

0.9037

R108

50 100 150 200 250 300 350 400 450

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

ln([

M0]/[M

t])

time (min)

R106

0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12

2000

3000

4000

5000

6000

Mn

conversion

0.9936

R106

0 500 1000 1500 2000 2500 3000 3500

0.0

0.2

0.4

0.6

0.8

1.0

ln([

M0]/[M

t])

time (min)

R110

0.1 0.2 0.3 0.4 0.5 0.6

0

5000

10000

15000

20000

25000

Mn

conversion

0.997

R110

60 80 100 120 140 160 180 200 220

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

ln([

M0]/[M

t])

time (min)

R124

0.05 0.10 0.15 0.20 0.25 0.30 0.35

1200

1400

1600

1800

2000

Mn

conversion

0.974

R124

Figure 5.6: ln([M]0/[M]t) vs. time and M n vs. conversion plots - from top tobottom, R108, R106, R110, R124 (see Table 5.1)

111


5.3.3 In-situ and Ex-situ End-modification of ω-nitroxide-functional

PS

The nitroxide moiety at the end of the grafted chains leads to crosslinking during

high temperature processing, due to high activation rate at high temperatures that

leads to termination by combination. Therefore, investigation on the end-modification

of PS was necessary. The end-modification was done both in-situ and ex-situ. In-situ

modification would be preferred, since the number of steps decreases and the probabil-

ity of termination reactions during the isolation of the polymer would be eliminated.

However, in-situ reactions performed in the model polymerizations resulted in initia-

tion of new chains. Free nitroxide radicals present in the solution end-cap the newly

initiated chains, therefore a linear increase is observed in ln([M]0/[M]t) vs. time plots,

with a sharp change in the slope (Figure 5.7).

R124

50 100 150 200 250

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

ln([

M] 0

/[M

] t)

time

thiol

addition

Figure 5.7: ln([M]0/[M]t) vs. time plot of R124 - The reaction conditions are inTable 5.1

The 1H NMR spectrum of the isolated PS after thiol treatment was indicating that

the SG-1 moiety remained. This could be due to the SG-1 moiety attached to the newly

initiated chains, or a non-complete end-functionalization. Therefore, the reaction was

done ex-situ, where no monomer is present to be initiated to form new chains. 1H

NMR spectrum showed that signals of SG-1 moiety at the end of the chain disappeared

(Figure 5.8).

The ex-situ modification was done at both 90 ◦C and 100 ◦C. After 45 minutes, the

112


ppm (f1)1.02.03.04.0

ppm (f1)1.02.03.04.0

(i)

(ii)

a

a

b

b

c

c, d, e

d

e f

g

h

h f g

Figure 5.8: Comparative 1H NMR spectra of PS - (i) PS bearing SG-1 moiety(before modification), (ii) PS after modification

reaction done at 90 ◦C showed no change in 1H NMR analysis. However, transformation

of nitroxide functional PS into hydrogen terminated PS was successful at 100 ◦C, which

is shown in Figure 5.8. The temperature should be 100 ◦C or higher in order to have

complete removal of nitroxide groups in 45 minutes. Ex-situ reaction shows that the

end-modification with thiol is successful. Therefore, the modification of TPE product

was done in-situ despite the fact that there will form new homopolymer chains, which

will not lead to crosslinking of the TPE.

5.3.4 Synthesis of NMP Macroinitiator

Characterization of the grafting product of NAP SG-1 initiator onto the EPM elas-

tomer was performed by FTIR. Figure 5.9 shows the comparison of neat EPM with

maleic acid and anhydride pendant functions and the macroinitiator with amic acid and

maleimide linkages. The assignments of the absorption frequencies of the corresponding

groups were mentioned in Chapter 3. The ring closure of amic acid into a maleimide

is done at 150 ◦C, where the alkoxyamine group dissociates. After ring closure of the

macroinitiator, the product was crosslinked. To circumvent this problem, the grafting

113


reaction from the macroinitiator was done without closing the ring. This leads to the

question about the thermal stability of the amic acid. The reaction of an anhydride

and an amine is known to be a thermally reversible reaction for low molar mass amines

[10].

1300 1400 1500 1600 1700 1800 1900

wavenumber (cm-1)

EPM-g-SG1 (imide)

EPM-g-SG1 (amic acid)

EPM-MAn

EPM-MA

Figure 5.9: Comparative FTIR spectra of EPM with different pendant func-tions - The spectra are shifted for clarity

The thermal reversibility of the amic acid linkage on the EPM was investigated by

FTIR. Figure 5.10 shows the shift in the signal from 1720 to 1705 cm−1 which indicates

that amic acid is converted into maleimide. The measurement is done at 100 ◦C, which

is the graft polymerization temperature of styrene from the macroinitiator.

FTIR analysis was also used for quantitative characterization of the grafting effi-

ciency of NAP SG-1 onto the EPM. Following the ring closure of the amic acid linkages

on the macroinitiator, an FTIR spectrum was taken. The remaining anhydride signal

was compared with the anhydride signal of neat EPM. In the case that no anhydride

signal was observed, the grafting was considered to be complete. Stoichiometric ratio

amine functions of NAP SG-1 to anhydride functions of EPM resulted in quantitative

coupling.

114


500 1000 1500 2000 2500 3000 3500

wavenumber (cm-1)

0

10min

20min

30min

40min

50min

1h

2h

3h

4h

5h

1450 1500 1550 1600 1650 1700 1750 1800

Figure 5.10: FTIR spectra of EPM-g-SG1 - Follow-up of absorption signals of pen-dant carbonyl functions as a function of time

5.3.5 Graft Polymerization of Styrene from Macroinitiator and In-

situ Modification of the Nitroxide Functionality

Graft polymerization of styrene was performed at 100 ◦C, at which the model reac-

tions showed highest propagation rate with minimum termination. ln([M]0/[M]t) vs.

time plot of a graft polymerization of styrene from EPM-g-SG1 macroinitiator is shown

in Figure 5.11, on the left hand side. R2 value of the curve is close to unity that the

graft polymerization was considered to be controlled.

The TPEs were synthesized by varying the molecular weight of grafted PS. Table 5.2

shows the parameters and the summary of the characterization results of the reactions

performed.

Table 5.2: Reaction conditions and results of graft polymerizations

Run St/EPM t(h) conv. M n %PS(w/w) (%) (PS)

R132 1 29 40 3500 28R134 2 35 18 3000 25R136 3 37 23 5000 40

The polymerization was followed by SEC as well. Besides the shift in the retention

time of the elastomer peak, formation of PS homopolymer was also observed (Figure

115


0 5 10 15 20 25 30

0.0

0.1

0.2

0.3

0.4

0.5

0.6

ln([

M] 0

/[M

] t)

time (h)

0.999

R132

0 5 10 15 20 25 30

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

ln([

M] 0

/[M

] t)

time (h)

thiol

addition

Figure 5.11: ln([M]0/[M]t) vs. time plot - the NMP of styrene from EPM-g-SG1(R132) before thiol addition (left), and that before and after the thiol addition

5.12). Homopolymer formation could be due to the remaining trace amounts of NAP

SG-1 in the macroinitiator during the work-up of its synthesis. However, the remaining

initiators worked as sacrificial initiator and homopolymer peak observed in the SEC

measurements were used for the estimation of the molar mass of the grafted PS chains.

The molar mass of grafted chains and free chains were considered to be the same [11].

The molar mass obtained from SEC measurements are in agreement with the theoret-

ically calculated value. In the same figure, a slight high molar mass shoulder starts to

form in the sample taken after 28 hours, which is indicative of heavier branching or

slight crosslinking.

UV traces of the samples were followed as a function of time during the graft

polymerization. An example for the run R134 is shown in Figure 5.13. The traces show

that the UV activity of the peak corresponding to the grafted product is increasing

(peak at 17.0 min), and after thiol addition, a slight decrease was observed (due to

the substitution of the alkoxyamine end-groups), and the intensity of the signal of

the sample taken after 3 hours showed no decrease in the UV activity of the grafted

product, which means the end-group modification is complete. Remaining UV activity

of the peak is due to grafted PS.

1-Dodecanethiol was added after a certain conversion was reached, and reaction

was kept at the same temperature. Following the thiol addition the polymerization

rate dramatically increased, which is shown in Figure 5.11, on the right-hand side.

However, no increase of the molar mass was observed in the homopolymer present in

116


14 16 18 20 22 24

0.0

0.2

0.4

0.6

0.8

1.0n

orm

aliz

ed

RI


4 h

16.5 h

28 h

Figure 5.12: RI traces of samples of R132 taken sequentially - Grafted product(peak at 17.0 min) and PS free homopolymer (peak at 22 min)

14 16 18 20 22

0.00

0.01

0.02

UV

sig

na

l (2

54

nm

)


t0

t10

t20

t35

t36

(a.t.)

t39

(a.t.)

Figure 5.13: UV traces of samples of R134 taken sequentially - UV traces duringpolymerization and after thiol addition (a.t.)

117


the mixture, which indicates that the elimination of the nitroxide was successful, and

thiyl radical formed by the hydrogen abstraction initiated new chains.

The change in the reaction rate is more significant in grafting reactions than in

the homopolymerization of styrene (compare Figure 5.7 and Figure 5.11). The rate of

polymerization after thiol addition in PS homopolymerization is two times larger than

that in graft polymerization, despite the fact that thiol was used in larger excess in

graft polymerization. The high viscosity of the medium results in slower diffusion of

the thiol compound into the elastomeric medium and slower propagation of the new

chains. However, propagation of the new chains is still much faster than the graft

polymerization rate relative to the rate of PS homopolymerization.

5.4 Conclusions

Synthesis of styrenic TPE with graft topology was successful with NMP ‘grafting

from’ approach. The alkoxyamine initiators used were found to be successful in control-

ling molar mass and the dispersity of the growing polymer. The modification of MAMA

SG-1 into NAP SG-1 was done in two steps and overall yield was 36%. Macroinitiator

was synthesized via amine-anhydride coupling of NAP SG-1 and EPM, and resulted

in high coupling efficiency. This indicates that the grafting density can be tuned by

varying the stoichiometry of the reactants. Trace amounts non-grafted alkoxyamine

initiator was the most probable cause of homopolymerization of styrene during the

graft polymerization. However, this trace amount of homopolymer gave an indication

for the progress of the molar mass of the PS growing from the macroinitiator, and the

performance of the thiol addition. Thiol worked successfully as a chain transfer agent

in these NMP reactions. Ex-situ reactions showed that thiol leads to the substitution

of alkoxyamine end-group with the labile hydrogen of the thiol, and the reaction is

complete in less than 1 hour at 100 ◦C. In-situ reactions lead to the initiation of new

chains and the continuation of the NMP of styrene, therefore the end-modification was

not observed in 1H NMR analysis. However, ex-situ reactions showed that the end-

modification with thiol is successful. Therefore, the end-functionalization of graft TPE

was possible to be done in-situ. The TPE products obtained at the end of NMP graft

polymerization and thiol treatment were soluble, indicating no significant crosslinking

is present. With ‘grafting from’ approach, it is found to be possible to tune the molar

118

5.4 Conclusions

mass of graft chains and end-modify them in-situ by quenching the polymerization by

a thiol at desired conversion.

119


120

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[2] P. De, M. Li, S. R. Gondi, and B. S. Sumerlin. Journal of the American ChemicalSociety, 130(34):11288–11289, 2008. 102

[3] G. Cheng, A. Bker, M. Zhang, G. Krausch, and A. H. E. Mller. Macromolecules,34(20):6883–6888, 2001. 102

[4] R. B. Grubbs, C. J. Hawker, J. Dao, and J. M. J. Frchet. Angewandte ChemieInternational Edition in English, 36(3):270–272, 1997. 102

[5] D. Roy, J. T. Guthrie, and S. Perrier. Macromolecules, 38(25):10363–10372, 2005.102

[6] C. J. Hawker, G. G. Barclay, A. Orellana, J. Dao, and W. Devonport. Macro-molecules, 29(16):5245–5254, 1996. 103

[7] C. Detrembleur, V. Sciannamea, C. Koulic, M. Claes, M. Hoebeke, and R. Jrme.Macromolecules, 35(19):7214–7223, 2002. 103

[8] E. Harth, C. J. Hawker, W. Fan, and R. M. Waymouth. Macromolecules,34(12):3856–3862, 2001. 103

[9] L. Petton, A. E. Ciolino, B. Dervaux, and F. E. Du Prez. Polym. Chem., 3:1867–1878, 2012. 103

[10] C. X. Sun, M. A. J. van der Mee, J. G. P. Goossens, and M. van Duin. Macro-molecules, 39(9):3441–3449, 2006. 114

[11] C. Bartholome, E. Beyou, E. Bourgeat-Lami, P. Chaumont, and N. Zydowicz.Macromolecules, 36(21):7946–7952, 2003. 116

121

BIBLIOGRAPHY

122

6

Structure-Property Relations of

TPEs with Graft Topology

Abstract

TPEs sythesized via various approaches, which are introduced and discussed in the

previous chapters, are investigated in terms of the relations between the molecular struc-

ture, morphology and thermomechanical and tensile properties of the material. The

graft TPEs with the ultimate properties are compared to TPEs with block topology.

The structure-property relations are investigated with respect to the coupling efficiency,

molar mass, composition and stoichiometry of the components, and the topology of the

samples. In this chapter, these parameters are introduced and data obtained via visual

and mechanical analyses of TPEs are elaborated and discussed in terms of achieving

ultimate mechanical properties.

123

6 Structure-Property Relations of TPEs with Graft Topology

6.1 Introduction

Thermal and mechanical properties of a material could be classified in two main cat-

egories: parameters determining the primary structure (composition and constitution),

and parameters determining the secondary structure (mesostructure or intermolecular

interactions). The primary structure is determined by the techniques used for macro-

molecular design, and it is supposed to not be affected by physical processes applied.

Secondary structure is also determined by the macromolecular design in the first place,

however, the thermal and mechanical processes affect the ultimate mesostructure.

Primary structure of a polymer is controlled by its composition, configuration and

constitution. Polymerization techniques determine the configuration and the consti-

tution of the polymer. An example could be the substituent groups on the metal

complexes used in metal-catalyzed polymerization of olefins that are determining the

stereoregularity of the polymer chain. The control on stereoregularity provides a con-

trol on the crytallization behavior of the polymer, which essentially determines the

secondary structure. Configurational and compositional characteristics of the metal

complex can also introduce constitutional changes, such as branching. Constitution of

a polymer could as well be adjusted just by choosing the monomers which have spe-

cific characteristics. For instance, maleic anhydride does not homopolymerize but only

copolymerize, of which the copolymerization with a co-monomer consequently may re-

sult in an alternating copolymer. Block and graft topologies are possible to build with

CRP techniques, which provides living chains to be transformed into various functions

that can be used for further polymerization or coupling reactions.

The secondary structure of a polymer is mainly determined by the primary struc-

ture. However, physical conditions as temperature or shear affect the way of physical

organization of the polymer chains. For instance, the heating rate determines the size

of the spherulites in polyolefins, which directly affects the morphology and resultant

properties of the material. Shear could convert the lamellar crystals into extended

chain crystals which consequently forms different microstructures, such as shish-kebab

morphology [1]. Crystalline parts, which have a different density and microstructure,

consequently behave as a different phase. This phenomenon is called crystallization-

induced phase segregation [2].

124


Fully amorphous polymers phase separate due to the thermodynamic incompati-

bility of the polymer chains. This is generally a result of the different compositions

of the chains. A blend composed of two incompatible polymer shows a macro-phase

separation, where the size of the phases is in the micrometer range. The size of the sep-

arated phases in blends could be decreased by compounds called compatibilizers, or by

modification both or one of the components, which enhances the physical interactions

between the two phases.

Synthesis of well-defined copolymer topologies exhibiting phase-separation by CRP

techniques is in fact the ultimate point of compatibilizing blends. Well-defined struc-

tures show well-defined and tunable properties. Control of the macromolecular archi-

tecture of the copolymers provides an extra level on controlling the phase separation

behavior of these materials. A review by Ruzette et al., which summarizes the re-

lation between the topology and self-assembly behavior of block copolymers mainly

synthesized by CRP techniques [3], claims that combination of molecular disorder

and self-assembly of well defined copolymers leads to unique properties of copoly-

mer/homopolymer blends.

In this chapter, TPEs synthesized via ‘grafting onto’ and ‘grafting from’ approaches

will be compared with each other and with commercial styrenic triblock copolymers in

terms of morphology, thermomechanical properties and tensile properties. TPE samples

are blends of graft copolymers and homopolymers of the components in various ratios.

This graft copolymer homopolymer blend results in a mixed morphology of macro-

phase separation and micro-phase separation. The aim of this study is to understand

the effect of the changes in the macromolecular design on the morphology and the

properties of the corresponding TPE.


6.2.1 Materials

TPE’s synthesized in Chapter 3, 4 and 5 were used as synthesized, poly(styrene-b-

ethylene/butylene-b-styrene) triblock copolymers (SEBS, Kraton grades G1650, G1652,

G1657 and G1730), toluene (Biosolve, AR), tetrahydrofuran (THF, Biosolve, AR) were

used as received.

125


6.2.2 Methods and Characterization Techniques

6.2.2.1 TEM Measurements of the Samples

All TEM grids were glow discharged prior to being used for sample preparation.

Each polymer sample was dissolved in toluene at 1 mg/mL concentration. A couple of

drops of solution were dripped in a petri dish containing a layer of water. After toluene

was evaporated, the formed polymer film was transferred to the TEM grid by carefully

submerging the grid in the water beneath the film layer with the help of tweezers and

dragging the grid upwards. The sample grids were placed on a petri dish and annealed

at 120 ◦C in a vacuum oven for 24 hours. Subsequently, EPM-g-PS sample grids were

vapor stained by ruthenium tetraoxide, and PB-g-PS sample grids were vapor stained

by osmium tetroxide for 15 minutes.

Phase separation behavior of the graft TPEs was investigated by transmission elec-

tron microscopy (TEM) measurements performed with a FEI Tecnai 20, type Sphera

TEM instrument with a LaB6 filament and operating voltage of 200 kV.

6.2.2.2 Compression Molding of the TPE Samples

Synthesized TPE samples were compression molded into rectangular molds with 0.5

mm thickness. Typically, compression mold with dimensions of 25 x 35 x 0.5 mm was

filled 1 g of TPE, compression molded between teflon sheets for 15 minutes under 200

bar at 130 ◦C.

6.2.2.3 DMTA Analysis of TPE Samples

Rectangular samples with dimensions of 15 x 5.3 x 0.5 mm were attached between

tension film clamps and measured within a temperature range from 100 ◦C to 200 ◦C at

a heating rate of 3 ◦C/min and a frequency of 1 Hz on DMA Q800 (TA instruments).

6.2.2.4 Tensile Tests of TPE Samples

Dumbbell-shaped tensile bars with dimensions of 35 x 2 x 0.5 mm and a parallel

specimen length of 17.5 mm were punched from compression-molded films. Tensile

tests were performed at room temperature with a constant speed of 1 mm/s on a Zwick

Z010 tensile tester equipped with 100 N force cell using TextXpert v7.11 software.

Three to six replicate measurements were performed for each material.

126


6.2.2.5 Interpretation of Data

In TEM images of EPM-g-PS and SEBS samples, the dark phases are the PS domain

and the light phases are the elastomeric domain (samples were stained by ruthenium

tetroxide). In TEM images of PB-g-PS samples, the dark phases are the elastomeric

phase and the light phases are the PS phase (samples were stained by osmium tetrox-

ide).

In DMTA measurements, the width of the rubber plateau was defined as the tem-

perature region between two T gs. The T g of the soft and the hard phases were obtained

by the tan δ vs. temperature curves. The storage modulus values of the rubber plateau

were taken from three different temperature points (E′1, E′2, and E′3) for the indication

of the temperature dependence.

The maximum stress (σmax), the stress at break (σR) and the strain at break (εR)

values of the samples were taken as the average of the measurements excluding the

highest and the lowest measurement value. Stress values were also recorded at 50%

strain (σ50) and 100% strain (σ100) if applicable.


TPE samples, the synthesis and characterization of which were discussed in Chapters

3, 4 and 5, were compared in terms of morphology and mechanical properties. The

chemical properties of the products of amine-anhydride coupling and thiol-ene coupling

discussed in this chapter are listed in Tables 6.1 and 6.3, respectively. Tables 6.2 and

6.4 show the mechanical properties of the products of amine-anhydride coupling and

thiol-ene coupling reactions, respectively. Samples prepared by nitroxide mediated graft

polymerization compared to styrenic TPEs with triblock copolymer topology will be

discussed in Section 6.3.6.

6.3.1 Morphology of the Graft TPEs: A General Comparison

The phase separation is the key concept of the thermoplastic elastomer behavior.

Both di/triblock copolymers and elastomer/thermoplastic polymer blends exhibit phase

separation. However, the size and the shape of the domains are strongly dependent on

the ordering behavior of the polymer chains constructing the mesostructure. This

127


Table 6.1: Chemical properties EPM-g-PS samples

Sample EPM/PS M n CEPS CEEPM

(w/w) (PS) (%) (%)C125 1 5800 67 577C128 2 10000 74 179C104 2 5800 75 326C118 2 10000 38 92C105 4 5800 70 152C106 5 2300 79 343C107 9 2300 80 177C119 4 10000 15 19C122 3 10000 30 50C124 2 2300 64 709C130 9 10000 56 31C141A 4 4800 19 51C141B 4 4800 20 63C141C* 4 4800 20 28C141D 4 4800 12 34C301** 4 6000 5 114C302 4 6000 11 15.6C114 3.3 5800 62 163C115 3.3 5800 62 163C116 3.3 5800 60 158C117 1 10000 37 179C120 9 10000 21 11C123 9 5800 52 50*EPM 25 kg/mol**Samples C301 and C302 are EPM-g-P(SMI)

phase behavior of the segments is one of the main parameters affecting the mechanical

properties.

A comparison of TEM images of EPM/PS blend, SEBS triblock copolymer (Kraton

G1652) and EPM-g-PS sample with 20 wt% PS content is shown in Figure 6.1. Kraton

G1652 is an SEBS triblock copolymer, with 30 wt% PS content. In general, a blend of

two imcompatible polymer exhibits macro-phase separation, as it is seen in the most

right image in the Figure 6.1, the size of the dispersed domain is in the micrometer

range. As far as these two components are compatibilized via the formation of covalent

bonds among incompatible chains, the size of the dispersed domains decreases (middle

image), and finally a material with incompatible segments completely covalently bonded

shows micro-phase separation (left image).

The EPM-g-PS sample used in Figure 6.1 is sample C105 (Table 6.2). This sample

has a 70% coupling efficiency with respect to the total PS content. The remaining 30%

PS consists of free chains and is present as a blend in the material. This results in a

mixture of macro and microphase separation in the morphology of the material, which

consequently leads to a heterogeneous morphology throughout the sample structure.

128


Table 6.2: Mechanical properties of the EPM-g-PS samples

Sample Tg Tg Storage modulus (MPa) σmax σR εR σ50 σ100(soft) (hard) E′1 E′2 E′3 (MPa) (MPa) (MPa) (%)

C125 -57 - 705 460 365 6.5 6.5 1.7 - -C128 -61 103 220 190 160 3.3 3.2 2.3 - -C104 -55 104 35 24 11 3.3 3.2 307.7 1.7 2.1C118 -54 - 230 190 165 1.4 1.4 1.2 - -C105 -56 - 14 9 3 1.3 1.7 273.4 1.2 1.4C106 -55 90 30 20 10 2.2 2.0 277.8 1.8 1.9C107 -56 93 3 2 1.5 0.4 0.3 138.8 0.4 0.4C119 -53 - 8 6 3 0.6 0.4 78.1 0.5 -C122 -56 105 60 45 25 1.3 1.3 5.1 - -C124 -59 89 180 130 90 3.9 3.0 194.8 3.4 3.6C130 -56 105 4 2 1 0.5 0.3 246.9 0.4 0.5C141A -54 - 6 2.5 1 1.1 1.0 256.7 1.0 1.1C141B -57 105 10 7 4 1.8 1.3 271.5 1.2 1.4C141C -56 - 7 4 2 0.4 0.3 80.3 0.3 -C141D -54 110 5 3 2 1.1 0.9 359.9 0.9 1.0C301 -58 - 6 3.5 1 0.9 0.62 145.6 0.9 0.9C302 -58 - 5 3 1 1.0 0.63 122.0 1.0 0.9C114 -51 99 40 30 17 2.0 1.6 67.3 1.8 -C115 -53 97 37 30 17 1.6 1.2 117.2 1.6 0.9C116 -53 97 45 35 25 2.1 1.7 107.3 2.0 1.8C117 -56 - 40 20 3 0.9 0.9 5.3 - -C120 -56 - 5 3 1.5 0.4 0.3 186.4 0.4 0.4C123 -51 - 5 3 1 0.4 0.3 158.8 0.4 0.4

6.3.2 Effect of Stoichiometry of the Components

6.3.2.1 Morphology

TPEs with graft morphology were compared in terms of PS content. Variation in the

weight fraction of PS does not make a significant difference in the morphology of the

samples. However, due to the presence of free PS and elastomer chains, materials show

a highly heterogeneous morphology. Sample C130 has a coupling efficiency lower than

sample C128, therefore the morphology of C130 is more heterogeneous than that of

sample C128. In Figure 6.2, the top two images belong to C130 showing the variation

of morphology in different areas of the sample due to the relatively lower coupling

efficiency. The bottom two images belong to the C128 sample, in which the variation

in morphology is less due to the higher coupling efficiency.

6.3.2.2 Thermomechanical Properties

Increasing the PS content in the TPEs increases the modulus regardsless of the

coupling efficiency, just due to the increased stiffness of the sample by the filler effect

of the PS. An example of a comparison between EPM-g-PS samples is shown in Figure

129


Figure 6.1: Comparative TEM images of a Kraton G1652 (left), EPM-g-PS(middle), and EPM/PS blend (right) - The scale bar is 100 nm, 200 nm and 500 nm,respectively

Figure 6.2: TEM images of EPM-g-PS samples - C130 (top), C128 (bottom), thescale bar is 200 nm

130


Table 6.3: Chemical properties of the PB-g-PS samples

Sample PB/PS M n CEPS CEPB

(w/w) (PS) (%) (%)112 2 2,500 32 128113 2 7,500 19 30140 1 14,000 48 69141 2 14,000 26 19142 4 14,000 25 9201* 1 5,000 16 64202 2 5,000 17 34203 4 5,000 22 22151A 4 1,600 56 174151B 4 1,600 23 72151C 4 1,600 30 94151D 4 3,400 56 83151E 4 3,400 29 43151G 4 3,400 44 66151H 4 7,000 55 39151J 4 7,000 40 29151K 4 7,000 43 31152A 4 3,400 17 25152B 4 3,400 40 59152C 4 3,400 24 36*Samples 201 and 202 are PB-g-P(SMI)

6.3.

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C104––––––– C123– – – – C105––––– ·

Universal V4.2E TA Instruments

Figure 6.3: Comparative modulus-temperature curves of EPM-g-PS samples -C104 (2:1), C105 (4:1), C123 (9:1)

C104 shows the highest modulus among the three due to the high PS content. Sam-

ple C123 exhibits an earlier yielding compared to other samples due to the insufficient

amount of grafted PS to keep the EPM chains intact.

131


Table 6.4: Mechanical properties of the PB-g-PS samples

Sample Tg Tg Storage modulus (MPa) σmax σR εR σ50 σ100(soft) (hard) E′1 E′2 E′3 (MPa) (MPa) (MPa) (MPa) (%)

112 -18 106 6 4 3 2.3 2.3 252.0 0.9 1.2113 -27 120 5 3 2 3.8 3.7 912.6 0.8 0.9140 -24 102 41 27 22 1.6 1.512 32.5 1.7 -141 -19 108 32 21 17 2.6 2.5 123.3 2.0 2.5142 -20 110 12 9 7.5 4.9 4.8 323.2 0.8 1.3201 -17 217 28 22 20 3.7 3.7 40.8 - -202 -25 216 5.4 3.7 3.4 3.3 3.2 199.5 1.1 1.8203 -26 216 1.5 1 1 4.0 3.9 456.4 0.7 0.9151A -26 81 4 2 1 2.4 2.4 1809.2 0.6 0.7151B -26 80 3.5 2 1 0.5 0.4 237.6 0.5 0.5151C -24 - 1.5 1.0 0.3 0.9 0.8 1340.6 0.5 0.6151D -21 95 2.5 1.2 0.5 3.6 3.6 1104.5 1.0 1.2151E -23 - 4 2.5 1.5 0.6 0.4 124.0 0.6 0.5151G -24 100 9 6 4 0.9 0.6 249.2 0.9 0.8151H -26 106 3 1.3 0.6 2.5 2.5 827.0 0.8 0.8151J -27 106 5 3 2 1.3 1.2 915.5 0.7 0.8151K -25 106 7 5 2.5 1.1 0.8 506.0 0.9 0.9152A -28 - 4 2 1.5 0.6 0.4 119.9 0.6 0.5152B -26 95 8 5.5 4.5 1.9 1.6 1103.3 0.9 1.1152C -29 90 5.5 3.5 2.5 0.7 0.5 142.6 0.7 0.6

6.3.2.3 Tensile Properties

Figures 6.4, 6.5, and 6.6 shows the comparative stress strain curves where the weight

fraction of PS varied for the samples with 2300 g/mol PS, 5800 g/mol PS and 10 kg/mol

PS, respectively.

Tensile modulus of the samples increases with the increasing PS content. Ultimate

strength of the samples with the highest PS content shows the highest value, as well.

The samples with the lowest PS content show lower strain at break values than the

neat EPM, most likely due to the destruction of the entanglements among the elastomer

chains during the coupling reaction.

6.3.3 Effect of Coupling Efficiency

6.3.3.1 Morphology

In amine-anhydride coupling reactions, coupling efficiency was varied by changing

the concentration of the reaction solution. In high concentrations (20% solid content),

high molar mass PS (∼10 kg/mol) and EPM phase separate due to low entropy of

mixing. Mixing can be enhanced by decreasing the molar mass of the components or

by diluting the reaction solution.

132


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neat EPM

C117

C119

C120

Figure 6.4: Comparative stress-strain curves of EPM-g-PS samples with PS of10 kg/mol - C117 (1:1), C119 (4:1), C120 (9:1)

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neat EPM

C104

C105

C123

Figure 6.5: Comparative stress-strain curves of EPM-g-PS samples with PS of5800 g/mol - C104 (2:1), C105 (4:1), C123 (9:1)

133


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neat EPM

C124

C106

C107

Figure 6.6: Comparative stress-strain curves of EPM-g-PS samples with PS of2300 g/mol - C124 (2:1), C106 (5:1), C107 (9:1)

Amine-anhydride coupling reactions were done in different solution concentrations

while keeping the molar mass of the building blocks and weight fractions constant.

TEM images of coupling products obtained from the batches C118 and C128 (Table

6.1 and 6.2) are comparatively shown in Figure 6.7. In these reactions the EPM/PS

weight ratio was 2:1. Solid content varied in the batches where the EPM/PS weight

ratio was 9:1 (samples C120 and C130). The comparison of TEM images of these

samples are shown in Figure 6.8.

Figure 6.7: Comparative TEM images of C118 and C128 sample - The scale baris 200 nm and the EPM/PS weight ratio is 2:1

134


Figure 6.8: Comparative TEM images of C120 and C130 sample - The scale baris 500 nm and the EPM/PS weight ratio is 9:1

At low coupling efficiency values, samples with high PS content (33% in C118 and

C128) show a phase inversion (Figure 6.7). Although the PS content is lower than 50%,

TEM image of sample C118 indicates that the material is similar to a PS plasticized

with EPM elastomer.

In thiol-ene coupling reactions, the coupling efficiency was varied by changing the

reaction temperature. The results were discussed in Chapter 4. TEM study has shown

that the size of the PS domain decreases with increasing coupling efficiency. The

morphology of PB-g-PS samples were compared to a PB/PS blend. Figure 6.9 shows

the comparison of a PB/PS blend and the TPE samples C151D, C151E and C151G.

The size of the PS domains is the lowest in sample C151D, which has the highest

coupling efficiency.


Figure 6.10 shows the comparison of modulus-temperature curves of the samples C120

and C130. Dilution, which overcomes the entropy barrier, allows the two polymer so-

lution to mix with each other. This entropy barrier becomes visible in the coupling

reactions at high concentrations where higher molar mass PS is used. This immisci-

bility negatively affects the coupling efficiency. The consequences of the low coupling

efficiency are apparent in morphological and mechanical characterization of the sam-

ples.

135


a) b)

c) d)

Figure 6.9: Comparative TEM images of PB/PS blend (a), C151D (b), C151E(c) and C151G (d) - The scale bar is 500 nm and the PB/PS weight ratio is 4:1

136


Dilution effect was analyzed in two different batch sets where EPM/PS weight ratio

was varied as a second parameter. Samples with low coupling efficiency show narrower

rubber plateau than those with higher coupling efficiency. This is due to the high

fraction of free elastomer chains starts to flow at lower temperatures, consequently

leading to failure.

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C130––––––– C120– – – –


Figure 6.10: Comparative modulus-temperature curves of EPM-g-PS samples- C120: low grafting yield, C130: high grafting yield

In Figure 6.10, C120 reaction was performed in concentrated medium , and C130

was in dilute medium. These samples have 10% PS content. Sample C130 has a wider

rubber plateau than sample C120. Samples C118 and C128 have 33% PS content.

These samples show the same trend, but with a higher modulus value due to higher PS

content.

The differences in coupling efficiency did not result in significant variation in the

modulus-temperature curves of the samples. A comparison of modulus-temperature

curves of PB-g-PS samples is shown in Figure 6.12 (sample properties Tables 6.3 and

6.4). While the effect of molar mass of PS is visible, the width of the rubber plateau

does not possess a parallel trend to the coupling efficiency values. This potentially

implies that a PB-PB conjugation might be taking place during compression molding,

this results in enhancement in the rubbery behavior of the samples, blurring the effect

of PB-PS coupling efficiency.

137


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Temperature (°C)

C118––––––– C128– – – –


Figure 6.11: Comparative modulus-temperature curves of EPM-g-PS samples- C118: low grafting yield, C128: high grafting yield

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Temperature (°C)

C151H––––––– C151J––––––– C151K––––––– C151D––– – – C151E––– ––– C151G––––– –


Figure 6.12: Comparative modulus-temperature curves of PB-g-PS samples -C151D, E, G, H, J and K (Table 6.4

138



A positive effect of coupling efficiency was observed in tensile properties of the sam-

ples as well. Strain at break was improved in samples with higher coupling efficiency.

Samples with 10% PS content show strain softening due to creep of the non-grafted

elastomer chains (Figure 6.13). Grafting efficiency in sample C130 is 68% with respect

to PS, and 31% with respect to EPM, which means that roughly 70% of EPM chains

are non-grafted. However, a slight recovery in the creep behavior is observed in sample

C130 relative to C120, due to the higher coupling efficiency in sample C130.

Tensile moduli of the samples C120 and C130 show no difference. However, among

the samples where PS content is higher (33%), sample C128 shows a lower tensile

modulus at lower strain, and the slope of the curve becomes even larger than sample

C118, despite their equal PS content. This indicates the smaller size of the hard domains

dispersed homogeneously in the elastomeric matrix allows the elastomer phase to be

dominant parameter determining the stiffness of the material at lower % elongation,

and at high % elongation the effect of crosslinks becomes observable. In literature, the

tensile behavior of C118 and C128 are referred as more brittle failure and more ductile

failure, respectively, where the transition from brittle to ductile behavior takes place

at phase inversion [4]. This behavior could also be concluded from the TEM images

of these samples, where C118 shows a continuous phase of PS domain, which could be

considered as the matrix, and C128 has the elastomer phase as the matrix.

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C120

C130

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C118

C128

Figure 6.13: Strain-stress curves of EPM-g-PS samples - Comparison of samplesC120 and C130 (left) C118 and C128 (right)

139


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C151H

C151J

C151K

Figure 6.14: Strain-stress curves of PB-g-PS samples - C151H, J, and K

The effect of PB-PB conjugation is more clear in the stress-strain curves of the

samples (see Figure 6.14). C151H has the highest coupling efficiency. Although the

sample C151K has higher coupling efficiency than C151J, it exhibits creep and the

sample C151J shows strain hardening similar to sample C151H. These materials were

still soluble after compression molding, however more pressure was needed to filter the

solutions through the 0.2 µm filter, which indicates slight PB-PB conjugation.

6.3.4 Effect of the Molar Mass of the Components

6.3.4.1 Morphology

All TPEs synthesized in this study have PS segments both as grafts and as free

chains in various fractions. The phase separation behavior of free and grafted PS chains

exhibit difference related to their molar masses. While low molar mass free chains tend

to contribute in the phases established by the grafted chains, high molar mass free

chains do not exhibit such a behavior [5]. This results in less defined phase separation

in samples with higher molar mass PS than those with low molar mass PS, despite

the close values of coupling efficiency. Figure 6.15 shows the phase separation behavior

of three EPM-g-PS samples synthesized with different molar mass PS. Additionally,

density of a polymer decreases with increasing molar mass. High volume fraction PS

could be also a reason for less defined phase separation.

140


Figure 6.15: TEM images of EPM-g-PS samples - left: C106 (PS 2300 g/mol),middle: C105 (PS 5800 g/mol), right: C130 (PS 10 kg/mol), the scale bar is 200 nm

Figure 6.16: TEM images of EPM-g-PS samples - left: C124 (PS 2300 g/mol),middle: C104 (PS 5800 g/mol), right: C128 (PS 10 kg/mol), the scale bar is 200 nm

141


In Figure 6.16, EPM-g-PS samples with 33% PS content are compared in terms of

PS molar mass. The coupling efficiency values of these samples are close to each other.

Although the sample C124 has relatively lower coupling efficiency, it exhibits the most

ordered morphology. This findings imply that higher molar mass PS chains have rather

a tendency to possess a macro-phase separation than low molar mass PS due to lower

entropy of mixing.


The effect of molar mass on mechanical properties is based on entanglement density

and T g. The entanglement molar mass of elastomers are around 2 kg/mol [6], [7], and

that of PS is 10 kg/mol [8]. The entanglements in PS are not a significant effect on the

stiffness of the material below its T g value. However, T g of a PS is strictly dependent

on the molar mass up to 10 kg/mol [8]. Thus, the width of the rubber plateau is

mainly dependent on the T g of the PS segment for the molar masses of PS used in this

study (below 10 kg/mol). In case of elastomers containing high molar mass PS, the

material would exhibit significant modulus after the T g of the PS due to the presence

of entanglements, however this region is not a part of the rubber plateau.

Figure 6.17 shows comparative thermal behavior of samples C124 and C128. C128

containing 10 kg/mol PS shows a wider rubber plateau than C124 containing 2300

g/mol PS. These two samples have equal PS fractions and close coupling efficiency

values. The difference in the width of the rubber plateau in this comparison is due to

the effect of the molar mass of PS on the T g of the hard phase.

Variation in the molar mass of EPM elastomer has a large effect on the rubbery

plateau (Figure 6.18). This is due to the lower number of entanglements per chain.

Entanglements among the elastomer chains play a role on rubbery plateau especially

in case of low coupling efficiency.


Comparative stress-strain curves of EPM-g-PS samples with various molar mass of

PS (Figure 6.19), show that the tensile behavior of the samples are directly related

to their phase separation behavior. While C128 shows a hard and brittle material

behavior, C104 shows a rather rubbery behavior and C124 shows a hard and tough

material behavior. C128 has the most heterogeneous morphology with the biggest PS

142


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C124– – – – C128––––– ·


Figure 6.17: Modulus-temperature curves of EPM-g-PS samples - C124 (PS 2300g/mol), C128 (PS 10 kg/mol)

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Temperature (°C)

C141C––––––– C141B– – – –


Figure 6.18: Modulus-temperature curves of EPM-g-PS samples - C141B (EPM50 kg/mol), C141C (EPM 25 kg/mol)

143


domains, consequently showing high tensile modulus and low stress and strain values at

break. C104 has a rather more dispersed phase of PS domains, maintaining the EPM

phase as a matrix. This sample exhibits a tensile behavior similar to a compatibilized

blend. The phase separation behavior of C124 is a microphase separation but co-

continuous and gyroid-like, which consequently results in tensile behavior of hard and

tough material, similar to high-impact PS [9].

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104

128

124

Figure 6.19: Stress-strain curves of EPM-g-PS samples - C124 (PS 2300 g/mol),C104 (PS 5800 g/mol) C128 (PS 10 kg/mol)

Comparison of stress-strain curves of EPM-g-PS samples with different EPM molar

mass (Figure 6.20) indicates the importance of entanglements between the non-grafted

chains and the grafted chains. The two materials compared have the same coupling

efficiency, however the tensile properties dramatically change due to the molar mass of

the EPM used.

6.3.5 Effect of the Composition of the Building Blocks

The TPEs containing P(SMI) copolymer have relatively lower coupling efficiency

values than the average value in TPEs with PS. Morphological studies showed that in

low coupling efficiency, the materials exhibit macrophase separation and heterogeneous

morphology. Due to these, the morphology of the TPE samples containing P(SMI) were

not investigated. Additionally, P(SMI) was not soluble in toluene, thus the preparation

144


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C141B

C141C

Figure 6.20: Stress-strain curves of EPM-g-PS samples - C141B (EPM 50 kg/mol),C141C (EPM 25 kg/mol)

of the TEM grids was not susceptible to the technique used in the preparation of TEM

grids of samples with PS.

6.3.5.1 Thermomechanical and Tensile Properties

All PB-g-PS and EPM-g-PS samples were compression molded at 130 ◦C, and PB-g-

P(SMI) and EPM-g-P(SMI) samples were compression molded at 200 ◦C for 15 minutes.

EPM-g-P(SMI) samples showed yielding at lower temperatures than PB-g-P(SMI) sam-

ples, first of all due to low coupling efficiency and slight crosslinking of PB-g-PS samples.

Comparative modulus vs. temperature curves are shown in Figure 6.21.

The T g of P(SMI) was obtained from tan δ vs. temperature curve of C201. T g

was not visible in C202 due to the lower P(SMI) content and partial crosslinking of the

sample. PB-g-P(SMI) samples were crosslinked to some extent due to the temperature

applied in compression molding in order to obtain homogeneous films. The T g of

P(SMI) is above 180 ◦C which is the temperature for PB to start crosslinking. This

result was found with a temperature study, which was done in order to investigate the

crosslinking behavior of PB during compression molding. Stress-strain curves of PB

sample compressed at different temperatures are shown in Figure 6.22. Compression

molded PB films at 110 ◦C, 130 ◦C and 150 ◦C were completely soluble in THF, however

the sample compressed at 180 ◦C was not soluble.

145


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Temperature (°C)

C301––––––– C302– – – – C201––––– · C202––– – –


Figure 6.21: Comparative modulus-temperature curves of TPE samples - PB-g-P(SMI) (C201 and C202), EPM-g-P(SMI) (C301 and C302)

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PB @ 110C

PB @ 130C

PB @ 150C

PB @ 180C

Figure 6.22: Stress-strain curves of PB films - PB samples were compression moldedat 110 ◦C, 130 ◦C, 150 ◦C and 180 ◦C for 15 minutes

146


6.3.6 Effect of Topology

The synthesized TPE samples were compared with triblock SEBS copolymers in

terms of morphology and mechanical properties. While well defined SEBS triblock

shows complete micro-phase separation (Figure 6.24), the TPEs with graft morphol-

ogy show heterogeneous morphology. The TPEs synthesized via the ‘grafting from’

approach contain free PS homopolymer as well as the TPEs synthesized via the ‘graft-

ing onto’ approach. This fact is certainly a factor in the formation of heterogeneous

morphology. However, the heterogeneous distribution of the pendant functionality on

the elastomer leads to a mixture of topologies from elastomeric backbone with a single

PS side chain to one with around twenty of PS side chains. This situation is poten-

tially the main effect on the heterogeneity of the morphology. TEM images of the TPE

samples synthesized via the ‘grafting from’ approach (Figure 6.23) show that the phase

separation behavior of the samples changes in different locations in the TEM grid of

the sample. Since, both of the morphologies seem to be in ordered state, this difference

was suggested to be due to the mixture of EPM chains with different extent of grafting.

Comparative DMTA curves of TPEs synthesized with graft polymerization (Table

6.5, and Table 6.6) and some SEBS triblock copolymers (Table 6.7) are shown in Figure

6.25.

Table 6.5: TPEs synthesized via graft polymerization

Sample %PS homopolymer M n

content (%) (PS)R132 28 8 3,500R134 25 8 3,000R136 40 15 5,000

Table 6.6: Mechanical properties of TPEs synthesized via graft polymerization

Sample Tg Tg Storage modulus (MPa) σmax σR εR σ50 σ100(soft) (hard) E′1 E′2 E′3 (MPa) (MPa) (%) (MPa) (MPa)

R132 -59 80 136 106 80 7.3 6.8 265.7 3.6 4.3R134 -62 51 173 128 78 4.7 4.2 367.4 2.3 2.5R136 -66 60 846 627 457 8.9 8.9 4.4 - -

DMTA analysis of the samples show that the rubber plateau of the samples with

graft topology is more temperature-independent than the that of samples with triblock

topology. This implies a stronger phase separation of the components, which could be

firstly due to the free PS homopolymer chains present in the structure. Additionally,

147


Figure 6.23: TEM images of EPM-g-PS samples - R132 (top) and R134 (bottom),the scale bar is 200 nm

148


Figure 6.24: TEM images of SEBS samples - G1652 (left), G1657 (right), the scalebar is 100 nm

0.1

1

10

100

1000

10000

Sto

rag

e M

od

ulu

s (

MP

a)

-100 -50 0 50 100 150

Temperature (°C)

RD132––––––– RD134– – – – RD136––––– · G1650––– – – G1657––– ––– G1730––––– – G1652–– –– –


Figure 6.25: Comparative modulus-temperature curves of TPEs - RD 132, 134and 136 are TPEs with graft topology and G1650, 1652, 1657 and 1730 are TPEs withblock topology

149


Table 6.7: Properties of SEBS triblock copolymers

Sample %PS type diblock M n σR εRcontent (%) (PS) (MPa) (%)

G1650 30 SEBS 0 10,000 35 500G1652 30 SEBS 0 7,500 31 500G1657 13 SEBS/SEB 30 5,500 23 750G1730 20 SEPS 0 7,000 9 880

0 500 1000

-5

0

5

10

15

20

25

30

35

40

en

gin

ee

rin

g s

tre

ss (

MP

a)

% elongation

1657

1650

R132

R134

R136

Figure 6.26: Stress-strain curves of TPEs - RD 132, 134 and 136 are TPEs withgraft topology and G1650 and 1657 are TPEs with block topology

the slope of the T g transition of the elastomer phase is higher in G1730 sample than

the G1650 sample and G1652 sample. Despite the fact that these three samples are

all pure triblock copolymers, the T g transition of the elastomeric phase in G1650 and

G1652 are not as sharp as that of the sample G1730. The modulus continues to exhibit

a decay following the T g transition. This is an implication for this stronger segrega-

tion to be due to the interaction parameter of the components. Despite the fact that

the molar mass of the elastomeric segments between the crosslinking points are more

polydispersed in TPE samples with graft topology than those in TPEs with triblock

topology, strong phase separation results in more temperature-independent rubbery

plateau.

Comparison of tensile properties of the TPEs with graft and block topology indicates

that the stress and the strain values of the SEBS triblock copolymers are higher than

the TPEs synthesized with graft topology. Figure 6.26 shows the comparison of the

stress-strain curves of some SEBS and EPM-g-PS samples.

The graft TPEs are not as strong as the TPEs with block topology. This is mainly

150

6.4 Conclusions

due to the heterogeneous topology of the graft TPEs. As mentioned in previous chap-

ters, EPM elastomer used in this study have a fraction with no maleic anhydride pen-

dant functions. This heterogeneity results in weak areas in the sample which cause

failure at lower strain and stress values.

6.4 Conclusions

TPEs synthesized via coupling techniques (the ‘grafting onto’ approach) have a

significant fraction of non-grafted free elastomer and thermoplastic polymer chains.

This non-uniform structure of the material leads to macro-phase separation and con-

sequently, the sample has a non-uniform morphology. Mechanical and morphological

characteristics of the TPE samples with low coupling efficiency is similar to a compat-

ibilized TPE blend.

Coupling efficiency is the main parameter determining the ultimate tensile strength

and the temperature window for the rubber plateau. Increasing coupling efficiency

results in more homogeneous and ordered phase separation, of which the effects are

directly observable in mechanical properties. Coupling efficiency is mainly affected by

the miscibility of the components, as discussed in the previous chapters. This immisci-

bility results in a more heterogeneous morphology, due to inhomogeneous mixing of the

components. Mechanical properties is directly affected by this heterogeneity. Materi-

als, which have low coupling efficiencies have narrower rubber plateau and lower stress

and strain at break values.

Molar mass of the PS has a significant effect on morphological and mechanical

characteristics of the TPE samples. Low molar mass PS tends to participate in the

ordered morphology of the sample. High molar mass PS tends to exhibit a phase

separation more macroscopically. This is mainly due to the incompatible nature of the

samples and furthermore to the high molar mass, both of which decrease the entropy

of mixing. Consequently, high coupling efficiencies are obtained in samples with low

molar mass PS, and these samples have a wider variety of grafting density values, which

results in different ordered morphologies in the same sample. Rubber plateau is directly

affected by the molar mass of PS due to the difference in T g of the hard phase. Molar

mass of PS is not a main parameter affecting the tensile properties due to the fact that

the molar mass range studied in this work is below the entanglement molar mass of PS.

151


Stoichiometry of the components does not have a significant effect on the morphol-

ogy of the samples when compared to other parameters such as coupling efficiency

and molar mass of the components. However, stoichiometry significantly affects the

mechanical properties. Tensile and storage modulus of the specimen increases with

increasing thermoplastic polymer content.

Ultimate characteristics of the TPEs with graft topology synthesized in this work

was achieved by the ‘grafting from’ approach. This approach resulted in TPEs with

the lowest amount of free PS, the most homogeneous and ordered morphology and

the highest tensile strength values. However, the elastomer used in this approach has

a high dispersity and heterogeneous distribution of the pendant functions. This fact

brings about the local weak points due to the non-grafted elastomer chains present in

the resulting TPE causing early failures in tensile strength measurements.

152

Bibliography

[1] F. Zuo, J. K. Keum, L. Yang, R. H. Somani, and B. S. Hsiao. Macromolecules,39(6):2209–2218, 2006. 124

[2] P. J. Barham, M. J. Hill, A. Keller, and C. C. A. Rosney. Journal of MaterialsScience Letters, 7:1271–1275, 1988. 124

[3] A. Ruzette and L. Leibler. Nature Materials, 4:19–31, 2005. 125

[4] I. S. Miles and A. Zurek. Polymer Engineering & Science, 28(12):796–805, 1988.139

[5] V. Abetz and P. Simon. Phase behaviour and morphologies of block copolymers.In Volker Abetz, editor, Block Copolymers I, volume 189 of Advances in PolymerScience, pages 125–212. Springer Berlin / Heidelberg, 2005. 140

[6] F. Mighri, M. A. Huneault, A. Ajji, G. H. Ko, and F. Watanabe. Journal of AppliedPolymer Science, 82(9):2113–2127, 2001. 142

[7] D. R. Daniels, T. C. B. McLeish, B. J. Crosby, R. N. Young, and C. M. Fernyhough.Macromolecules, 34(20):7025–7033, 2001. 142

[8] P. G. Santangelo and C. M. Roland. Macromolecules, 31(14):4581–4585, 1998. 142

[9] G. Dagli, A.S. Argon, and R.E. Cohen. Polymer, 36(11):2173 – 2180, 1995. 144

153

BIBLIOGRAPHY

154

7

Outlook

Conventional TPEs with block topology consisting of hard and soft blocks are suc-

cessful in many applications in which solvent resistance, high shear or hih tempera-

ture stability are not the most important parameters. However, the polymerization

and processing techniques of these materials still have some drawbacks, such as the

high sensitivity of anionic polymerization and necessity of very high temperatures to

achieve the disordered state. In this dissertation alternative polymerization TPE ma-

terials with an alternative topology (graft copolymer) was introduced and investigated.

The structure-property relations of these elastomeric, phase-separated materials were

investigated in detail from a topologic point of view.

The key concept for excellent and tunable properties is the precise control over the

molecular structure. The ‘grafting onto’ approaches generally result in incomplete cou-

pling with respect to the thermoplastic precursor due to the fact that end-functionality

of the thermoplastic component is never 100%. This is not the main problem, since

the free thermoplastic chains with relatively low molar mass tend to diffuse into the

domains formed by the grafted thermoplastic chains in sufficiently high coupling effi-

ciencies. As a result, they do not have negative effects on mechanical properties of the

resulting TPEs. However, the thermoplastic content should be kept under a certain

value in order to prevent phase inversion, which brings about a limitation in the stoi-

chiometry of the reacting functional groups. Furthermore, a thermoplastic component

with a sufficiently high molar mass should be used for a proper T g of the hard phase,

which introduces a challenge in terms of entropy of mixing during coupling. The limita-

tion in the volume fractions of the components leads to an unbalanced stoichiometry of

155

7 Outlook

the functional groups, which prevents the elastomer chains to be completely grafted in

the cases where TPE samples contain high molar mass thermoplastic precursor. Non-

grafted elastomer chains dramatically decrease the tensile properties of the resulting

TPE.

Among the ‘grafting onto’ chemistries used in this work to obtain a TPE with graft

topology, amine-anhydride coupling was found to be a more straightforward technique

than the thiol-ene coupling, except for the necessity of dry conditions. Thiol-ene cou-

pling has inevitable homopropagation as a side reaction, especially in the cases where

excess vinyl is used. Furthermore, quantitative yields were obtained in amine-anhydride

coupling reactions. However, due to the lack of polymer precursors to be coupled, the

tensile properties were not optimum. Additionally, the quantitative yields were only

valid for the reactions where relatively low molar mass PS was used. Conclusively, the

success of polymer-polymer coupling reactions between two incompatible high molar

mass polymers is limited due to the physical conditions, even if the polymer precursors

are very well-defined. The ‘grafting onto’ approach may be preferred over the ‘grafting

from’ approach, for the sake of convenience in monomer and solvent-free melt process-

ing techniques for the industrial applications. In that case, the physical challenges

should be surpassed with high temperature and shear, maximizing the interfacial area

between two incompatible components. In this regard, CRP techniques are being fastly

developed towards straightforward industrial applications [1] [2] [3], which will enable

the production of well-defined building blocks with end or pendant functionalities. This

achievement will enhance the potential for producing copolymers with various topolo-

gies with polymer processing techniques including robust coupling reactions.

The ‘grafting from’ approach is more convenient than the ‘grafting onto’ approach

in terms of complete and more uniform grafting of the elastomer chains, since there are

no compatibility issues between the elastomer and the monomer. The thermoplastic

chains grow from each initiating moiety. If the elastomer is uniformly modified (no non-

functional chains), the resulting TPE will be free of non-grafted elastomer chains, and

optimum tensile properties may be acquired. From this point of view, the graft copoly-

merization of styrene with N-phenyl maleimide or maleic anhydride from a well defined

elastomeric macroinitiator via nitroxide mediated radical polymerization (NMP) seems

a promising approach to have the ultimate properties of a TPE with a graft topology.

The commercial NMP initiator MAMA SG-1 is a good candidate for the modification of

156

the functional elastomer, thanks to its carboxylic acid function that may be employed

directly or converted into various desired functions. Simple coupling reactions, which

exhibit quantitative yields at ambient temperatures (such as amine-anhydride coupling)

could be used for the grafting of the NMP initiator onto functional elastomers. The

choice of the solvent could be a challenge due to the high temperatures used for the

polymerization and the fact that olefinic elastomers and N-phenyl maleimide monomer

have a limited number of common solvents. Alternatively, the reaction could be done

in bulk, but in that case the polymerization conditions should be optimized by using

additional nitroxide radicals to control the propagation, since the polymerization rate

of copolymerization of styrene and maleimides or maleic anhydride is higher than that

of the homopolymerization of styrene.

The TPEs synthesized with a minimum amount of free PS chains in this study were

found to have a lower temperature-dependent modulus than that of the conventional

linear triblock SEBS copolymers. A lower temperature dependence of the rubbery

plateau modulus indicates that the material maintains a stable rubbery behavior within

the temperature range of the rubbery plateau. However, the tensile properties of the

graft TPEs prepared in this study were found to be lower than those of the TPEs

with triblock topology. This was mainly due to the lack of uniformity in the the

structure of the graft TPEs. In this regard, the elastomer precursors should be chosen

or synthesized with the requirement of having a low dispersity and uniformly distributed

pendant functions, in order to achieve the ultimate mechanical properties of TPE with

a graft topology.

A TPE with a well-defined graft topology is potentially superior to a TPE with

a block topology in terms of melt processing. Block copolymers have limitations in

accessing order-disorder transitions during melt processing, due to high molar mass

of the hard block that is necessary for sufficient tensile strength [4]. Studies done in

silico showed that alternative topologies lower the order-disorder transition tempera-

ture compared to linear block topology and therefore potentially are more convenient

for melt processing [5]. In this regard, a theoretical study should be performed for

estimating the phase separation behavior of the graft copolymers, of which to the best

of the author’s knowledge no examples have been found in literature.

While targeting for the ultimate mechanical properties of the TPEs with graft topol-

ogy, one of the main drawbacks could be the dangling ends of the elastomer backbone.

157

7 Outlook

Sufficiently long dangling ends may have sufficient entanglements that will not induce

a severe decline in the tensile properties. However, this condition will necessitate very

high molar mass elastomers, which challenges the melt processing conditions and limits

the options for constitutional structure of the resulting TPE. In this regard, the elas-

tomeric precursor should contain reactive groups not only as a pendant function along

the chain, but also at the chain ends. Alternatively, combination of block and graft

topologies could be a synergistic solution for reaching both the ultimate mechanical

properties and the enhancement of melt processing conditions.

158

Bibliography

[1] W. A. Braunecker and K. Matyjaszewski. Progress in Polymer Science, 32(1):93 –146, 2007. 156

[2] J. Nicolas, B. Charleux, and S. Magnet. Journal of Polymer Science Part A: Poly-mer Chemistry, 44(13):4142–4153, 2006. 156

[3] C. Barner-Kowollik and S. Perrier. Journal of Polymer Science Part A: PolymerChemistry, 46(17):5715–5723, 2008. 156

[4] N. A. Lynd, F. T. Oyerokun, D. L. ODonoghue, D. L. Handlin, and G. H. Fredrick-son. Macromolecules, 43(7):3479–3486, 2010. 157

[5] G. M. Grason and R. D. Kamien. Macromolecules, 37(19):7371–7380, 2004. 157

159

BIBLIOGRAPHY

160

Summary

Rubbery behavior with a consistent modulus over a wide temperature range is a

challenge in the search for ultimate structure-property relations of thermoplastic elas-

tomers (TPEs). This feature is closely related to the phase separation behavior and

the constitution of the segments and the T g of the phases.

Elastomer/thermoplastic blends and tri-/multi-block copolymers are industrial prod-

ucts that were developed to get desired mechanical properties and ease of processability

in TPEs. TPEs show a transition between elastic and viscous behavior with respect to

the applied temperature. They are acknowledged to be an alternative to vulcanized rub-

bers, since TPEs can be melt-processed thanks to their physically -crosslinked structure

as opposed to the chemically crosslinked structure of conventional rubbers/elastomers.

Current methods applied in industry to produce tri-/multi-block copolymers are

polycondensation and anionic polymerization, which both have disadvantages in terms

of either robustness, variety of suitable monomers or consistency of the mass distri-

bution. Controlled radical polymerization (CRP) methods, which are Atom Transfer

Radical Polymerization (ATRP), Nitroxide Mediated Polymerization (NMP) and Re-

versible Addition-Fragmentation chain Transfer (RAFT) polymerization are relatively

more robust and elegant techniques that provide well-defined functional polymers with

low dispersity. These well-defined functional polymers can be further used as building

blocks to design copolymers with various topologies.

In this PhD study, TPEs with graft topology are synthesized and structure-property

relations are investigated. Various living radical graft polymerization techniques are

used for the synthesis of high T g thermoplastics. These high T g polymers are grafted

on a functional elastomeric backbone via two different approaches, which are ‘grafting

161

Summary

onto’ and ’grafting from’. In the ‘grafting onto’ approach, ATRP and RAFT poly-

merization techniques are used to synthesize high T g thermoplastics that are subse-

quently grafted onto the elastomeric backbone by polymer-polymer conjugation reac-

tions, namely anhydride-amine coupling and thiol-ene coupling, respectively. NMP is

used in the ‘grafting from’ approach in which high T g polymer is grown from the initiat-

ing sites of the modified elastomeric backbone. Maleated poly(ethylene-c0-propylene)

rubber (EPM) is used for amine-anhydride coupling reactions in the ‘grafting onto’

approach, and it is modified into a macroinitiator for the ‘grafting from’ approach.

Polybutadiene (PB) with a high external vinyl content is used for thiol-ene coupling

reactions in the ‘grafting onto’ approach.

Structure-property relations are investigated in terms of molecular architecture,

morphology and thermal/mechanical properties. Size exclusion chromatography (SEC),

Nuclear Magnetic Resonance Spectroscopy (NMR) and Fourier Transform Infrared

Spectroscopy (FTIR) techniques are used to characterize the compositional and con-

stitutional structure of synthesized TPEs. Transmission electron microscopy (TEM)

analysis is performed for the morphological characterization and phase separation be-

havior of the samples. Dynamic mechanical thermal analysis (DMTA) and tensile tests

are performed for analyzing the thermal and mechanical properties. Relation between

the molecular architecture, phase separation behavior and thermal/mechanical proper-

ties are discussed in terms of a variety of structural features of the TPEs.

The ‘grafting from’ approach is found to be the more robust and efficient technique

for the synthesis of TPEs with graft topology. Graft polymerization of the monomer

from the elastomeric macromonomer results in relatively more well-defined topology

compared to the ‘grafting onto’ approach. Morphology studies show that the phase

separation behavior of the TPEs synthesized via the ‘grafting from’ approach is more

uniform. Synthesized TPEs show ordered phase separation as long as their molecular

structure is close to uniformity. Ordered phase separation is observed in the samples

with high coupling efficiency.

The ‘grafting onto’ approach results in ill-defined products with non-uniform and

incomplete grafting due to the immiscibility of the components especially in the cases

where high molar mass components are used. These products show heterogeneous

morphology with both micro and macro-phase separation.

162

Stiffness of the synthesized materials is found to increase with the increasing ther-

moplastic component content, regardless of the coupling efficiency. DMTA analyses

show that the coupling efficiency and the molar mass of the thermoplastic component

increase the temperature range for the rubbery plateau. Tensile tests show that the

coupling efficiency increases the stress and strain values at break. The molar mass of

the thermoplastic component does not have an effect on tensile properties due to the

fact that the entanglement molar mass for the thermoplastic component is not exceeded

for the polymers synthesized in this study.

The effect of composition of the thermoplastic component on the coupling efficiency

with elastomers and on the properties of the resulting materials is studied by comparing

PS with P(SMI). The miscibility of P(SMI) is lower than that of PS with the elastomers

used. The coupling efficiency cannot be enhanced due to the low entropy of mixing

in high reaction concentrations, and to the necessity of high dilution to overcome the

entropy barrier. Coupling reactions of P(SMI) and EPM, which are carried out in a

binary solvent mixture (1,4-dioxane-toluene), shows an increase in coupling efficiency

at lower concentrations of the reaction mixture. This is believed to be due to the

high miscibility of PB soultion in toluene and P(SMI) solution in 1,4-dioxane. Binary

solvent approach is promising to enhance the coupling efficiencies in reactions where

highly immiscible components are used.

Characterization techniques are used for the comparison of the synthesized TPEs

with graft topology with commercially available styrenic TPEs with tri-block topology.

While TPEs with graft topology showed a more temperature-independent rubbery be-

havior, stress and strain values at break were not as high as the TPEs with tri-block

topology. This is due to the high dispersity and the non-uniform pendant functional-

ity of the elastomer used resulting in weak domains in the structure of the resulting

material having early failures in tensile tests.

In conclusion, styrenic TPEs with graft topology are alternative to the styrenic

TPEs with block topology in terms of lower melt viscosities. Additionally, in the case

of low dispersity and highly uniform pendant functionality of the elastomer, the tensile

properties are promising to be competitive with that of the TPEs with block topology.

A combined molecular architecture of block and graft topologies is believed to be the

synergistic solution for the dilemma between the melt processability and good tensile

properties.

163

Summary

164

Acknowledgements

First of all, I would like to thank my promotor prof.dr. Bert Klumperman for his

guidance in this work. Bert, you are the most proper supervisor I could ever have

worked with. Your were so patient, optimistic and confident about me throughout the

study. I was never sure that I can manage all this, but there was you who had a big

reliance on me. Thank you so much for the mental support and the fruitful discussions.

Secondly, I am very thankful to my co-promotor dr. Martin van Duin, who guided

me with a great motivation and rationality. Martin, you taught me how to work in an

efficient way, to find simple answers for chaotic questions, to make clear points, and to

be rational and critical. I am so grateful for your very synergetic supervision.

My reading committee, prof.dr. Jan Meuldijk, prof.dr. Metin Acar, prof.dr. Ton

Peijs, and dr. Han Goossens are greatly acknowledged for their interest and efforts for

the enhancement of my thesis. Additionally, prof.dr. Alex van Herk, for his accep-

tance to be in my extended committee and for all his help and sincere collaboration

throughout my PhD life in TU/e.

SPC secretaries, Pleunie Smits and Caroline van Os-Rovers are many thanked for

all their sincere help and understanding in every issue of mine. Pleunie, thank you very

much for the warmth you gave which I feel from the first phone talk. Caroline, thank

you for all the cigarettes I smoke from you and for your one eye on me to take care like

a mother.

Thanks also go to Hanneke Lambermont-Thijs, Karin Dietz and Harry Philipsen for

MALDI-TOF-MS and GPEC measurements. Especially I would like to thank Hanneke

for her great help and support by optimizing the GPEC measurements of the TPEs.

Thanks also go to the former technical staff, Wieb Kingma and Wouter Gerritsen for

the nice time we shared in the labs, breaks and out of working hours. Rinske Knoop is

165

Acknowledgements

greatly acknowledged for her guidance in TEM measurements, and for nice chats and

the neighbourhood.

SKT people are many thanked for their understanding, help, patience and for letting

me use their machines and make some fumes around :) Anne Spoelstra is greatly

acknowledged for the scientific support and guidance for TEM measurements, Pauline

Schmit, Bob Fifield, Bjorn Tuerlings, Gizela Mikova, and Elena Miloskovska for the

instructions of the machines and their great sincere help whenever I needed it.

I would like to thank Martin Fijten for letting me use his expertise for SEC mea-

surements, for every kind of technical and scientific support, inspiring discussions, and

for being a perfect collaborator, and being a very sweet and trustworthy friend for all

times.

I am so grateful to dr. Dario Cavalli, dr. Rafael Sablong, Martin Ottink, Fabian

Karbach and Mark Pepels for discussing with me and teaching me in mini brainstorming

sessions and discussions and being patient enough to listen to my neverending and non-

understandable questions. Additionally, dr. Gijs Habraken is deeply acknowledged for

being the idea-father of the NMP chapter and sharing his own SG-1s with me.

Bahar Yeniad is greatly acknowledged for being my every-time-every-type sup-

porter, financial-mental sponsor and backer. Life in Eindhoven would not be this

meaningful, and complete if you were not here. I know, for you it’s just the opposite,

you damn the day you came to the same office with me, and you left me as soon as

you got the first chance :) But you love me sometimes, I know... And a bit Turk-

ish, seninle karsilasmis olduguma, hayatinin icine kendimi, hayatimin icine seni, cok

tesadufi sekillerde ve hic yokolmayacak bir halde sokmus olmaktan aslinda cok mem-

nun ve mutluyum. Benimle herseyini paylastigin icin cok cok minnettarim, ve bundan

sonra da umarim hep yaninda olabilirim :). Hayatta basina gelen hersey sana mutluluk

getirsin!

Camille Descour is also greatly acknowledged for her every-time-every-type support,

which was not less than Bahar. You are the coolest and the strongest girl I have ever

seen. The way we understand each other is very unique and very special to me. It

doesn’t mean that you speak French and I speak Turkish and somehow we understand

each other (actually it happens sometimes). I am very thankful for all the food, the

cigarettes, the clothes, the shoes, the car, the bed, the house, the events, the anger, the

happiness, the joy, the thoughts that you shared with me, and for everything you did

166

for me, which I cannot even list. I don’t think I can ever pay all these things back. But

you know, I will be with you whenever you tell me to and I will never play someone

else.

Seda Cantekin specially acknowledged for being the reason why I am here. I am not

in love with her but I love her :)). Seda, o e-maili attigin icin, mulakata geldigimde bana

evini actigin icin, sonrasinda da hep yanimda oldugun icin ve icten dostlugunu benimle

paylastigin icin cok tesekkur ederim. Paylastigimiz hersey hep cok anlamliydi. Sana

buyuk mutluluklar ve bol sans dilerim, ve hep yakinlarinda olacagima soz veriyorum.

My mom, Gulcin Tuzcu, my dad Sukru Tuzcu, my sisters Gamze Muslu and Gaye

Baykut, my brothers in law Yasar Muslu and Can Baykut, my nieces Ece Muslu and

Irem Baykut, and my nephew Emre Baykut are greatly acknowledged for their endless

love, support and for being the great family of mine. Beni ben yaptiginiz icin size ne

kadar tesekkur etsem az, bir evlat ailesine olan borcunu nasil odeyebilir bilmiyorum

ama sanirim bunun icin yasiyorum.

The people who I shared home with, Irmak Aladagli, Baris Yagci, Ozan Dogu

Tuna and Mark Berix, thank you for sharing your life in Eindhoven with me. Irmak,

ilk goz agrim :), benim icin yaptigin tum karsiliksiz deger bicilmez iyiliklerin icin,

buraya geldigim zaman, hem annem hem kardesim hem arkadasim oldugun icin cok

cok tesekkur ederim. Eindhovendaki ailemin bas mudavimi, her zaman birlikte olmak

dilegiyle, hersey her zaman gonlundeki gibi olsun. Baris, abi seni cok seviyorum, sonsuz

dostlugun, ictenligin, guvenin, ay artik iyice melankolige bagladim, yani seni anlatmak

cok zor, dunyaya cok seyrek gelecek bir insan tipisin, ama bana daha da bir ozelsin,

neden bilmiyorum, bana hayat asiliyorsun... Paylastigimiz ev, bolum, the Endings,

beraber yasadigimiz hersey, kocaman kucaklamalarin icin cok cok tesekkur ederim,

dunyada iyi olan ne varsa seninle olsun. Ozan, yani iyi ki Hollanda’ya master yapmaya

gelmissin, iyi ki senin gibi bir insani tanima serefine ermisim. Tum harika muhabbetler,

tartismalar, yemekler, muzikler icin cok cok sagol! Mark, thank you for introducing

the epic Limburgse life, and the concept of being homies for life. You are a great man,

and you deserve the very best things where Murphy’s got no guts to ruin anything.

Sinan & Ceylan Oncu are greatly acknowledged for making me feel home in every

moment I was with them. Canlarim, n’olur hep goruselim ilerideki yillarda da. Cok gec

buldum ben sizi hayatimda, ama gec olsun guc olmasin! Harika insanlarsiniz ve sizi cok

seviyorum, valla bilmiyorum, sakin eskimeyin, hayatin sizi yormasina izin vermeyin..

167

Acknowledgements

Bole bir korku kaplar ya insanin icini sevdigi insanlari dusununce ya da benim ole oluyo

bilmiyorum, sizi pamuklara sarip saklamak istiyorum..

The people I shared the lab with, Patricia Geleen, Hector Tello Manon, Martin

Ottink, Marie-Claire Hermant, Evgeniy Tkalya, Rutger Knoop, Dogan Gunbas, Albert

Jeyakumar, Julien van Velthoven, and the new joiners Lili and Mischa, thank you for

nice work environment. The special thanks are for Patricia, Hector and Martin who

helped me so much to find my way in the lab. Hector, you are an arsehole, this is

something apart, I will never forget the time that you made me weep like hell, it’s so

special :)) Thanks also go to Judith Canadell, my official labbudy despite the fact that

we never shared the same lab :), thank you for all the effort to help me around. Joris

Salari is thanked for the nice times together both in the Netherlands and South Africa,

finding my nickname, and all the chats and various things we did together. MC, you’re

a special person for me, I wish you all the best.. My colleagues/friends in SA, Rueben

Pfukwa, Aimee Sutherland, Waled Hadasha, Niels & Zaskia Akeroyd and Eric van den

Dungen are greatly acknowledged for their great help around the lab and their sincere

friendship and company making the time I spent in SA very hilarious.

And finally my students, they are the last I thank but they should be the first,

students do the most annoying thing, the crappy lab work. Politeness killed the cat :))

Rik Diepenhorst is many thanked for his interest and diligence in the project we carried

out together, which worked out as his gradution project and the skeleton of Chapter

5. Rik, I wish you all the best for your rest of your life, and thank you for being a

great team-worker. Elif Zengin is many thanked for the nice work she did on thiol-ene

coupling approach in her summer internship. Elif, I wish you good luck and success in

your masters and a happy life ever after, hopefully we see each other in between.

There are so many more names which must be mentioned actually, but it’s so hard

for me to write the time more than four years down (taking ’the last minute personality’

into account). I am happy that I was here, with all of you guys. This PhD time was

a different dimension of my life that I will never get out. I think I can’t get out :)

I am serious that I met so many great people here, thank you all for being yourself

and being just yourself. I hope I will see each one of you somewhere sometime in my

life, preferably in a warmer and less rainy place. After getting this PhD, I hope I will

have enough money and freetime in the future (so hopeful) that I can travel around

the world to meet everyone I have once shared something with.

168

Curriculum Vitae

Gozde Tuzcu was born on 10th April 1983 in Izmit, Turkey. After graduating from

Ankara Science High School in 2001, she started her undergraduate study at the depart-

ment of Chemistry in Middle East Technical University. After obtaining her Bachelor

of Science degree in 2006, she started her postgraduate study at the department of

Polymer Science and Technology in the same university and joined the research project

on concrete admixtures, which was under the supervision of prof.dr. Leyla Aras and

financially supported by the research fund (BAP) of Middle East Technical University

and Baskent Yatirim A.S. She obtained her Master of Science degree in 2008, with a

thesis on the synthesis of polycarboxylate based copolymers with different topologies

and their application as a superplasticizer in concrete. Subsequently, she started her

PhD study on April 2008 at the department of Chemical Engineering and Chemistry in

Eindhoven University of Technology, under the supervision of prof.dr. Bert Klumper-

man. The most important results of this study are presented in this dissertation.

169

Curriculum Vitae

List of Publications

• Tuzcu, G., van Duin, M., Klumperman, B., ”ARGET ATRP as a first step to-

wards ’grafting onto’” NATO Advanced Study Institute Meeting, (2008). (poster

presentation)

• Buyukyagcı, A., Tuzcu, G., Aras, L., ”Synthesis of copolymers of methoxy polyethy-

lene glycol acrylate and 2-acrylamido-2-methyl-1-propanesulfonic acid: Its char-

acterization and application as superplasticizer in concrete” Cement and Concrete

Research 39 (2009), pp. 629 - 635. (article)

• Tuzcu, G., van Duin, M., Klumperman, B., ”Graft thermoplastic elastomers via

polymer-polymer conjugation” IUPAC 9th International Conference on Advanced

Polymers via Macromolecular Engineering, (2011). (oral presentation)

• Tuzcu, G., van Duin M., Klumperman, B., ”Graft thermoplastic elastomers via

polymer-polymer conjugation: 1. Amine-anhydride coupling” (article, in prepa-

ration)


polymer-polymer conjugation: 2. Thiol-ene coupling” (article, in preparation)


NMP: A ’grafting from approach’” (article, in preparation)

• Tuzcu, G., van Duin M., Klumperman, B., ”Graft thermoplastic elastomers:

Structure-morphology-property relations’” (article, in preparation)

170

Documents

Thermoplastic elastomers via controlled radical …Thermoplastic Elastomers via Controlled Radical Graft Polymerization PROEFSCHRIFT ter verkrijging van de graad van doctor aan de