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Chapter 4. Chemical Structure and Polymer Properties
4.1 Introduction
4.2 Fabrication Methods.
4.3 Mechanical Properties
4.4 Thermal stability
4.5 Flammability and Flame Resistance.
4.6 Chemical Resistance.
4.7 Degradability
4.8 Electrical Conductivity
4.9 Nonlinear Optical Properties
POLYMER CHEMISTRY
A. Relationship between chemical structure and polymer properties. a. Chemical structure and morphology (Chapter 3). b. Polymer properties : mechanical property, thermal property, chemical property, electrical property, etc.
B. To tailor chemical structure for specialty polymer.
C. Additives - compounds to modify polymer property.
D. Fabrication method to make polymer articles.
4.1 Introduction
POLYMER CHEMISTRY
4.2 Fabrication Methods.
A. Molding a. Compression molding : thermoset polymer.
FIGURE 4.1. Compression molding
POLYMER CHEMISTRY
b. Injection molding : thermoplastic polymer.
FIGURE 4.2. Injection molding. [Reprinted from V. Hopp and I. Hennig, Handbook of Industrial Chemistry, copyright 1938, courtesy of McGraw-Hill.]
POLYMER CHEMISTRY
c. Reaction injection molding (RIM)
FIGURE 4.3. Basic components of a reaction injection molding (RIM) process. [From Modern Plastics Encyclopedia, 1984-85. Reprinted with permission of Modern Plastics.]
newly developed molding. polyurethane and other polymer system.
POLYMER CHEMISTRY
d. Reinforced reaction injection mold (RRIM) : Modified RIM for fiber reinforcement. e. Blow molding : for bottles.
FIGURE 4.4. Blow molding. [Courtesy of the Society of the Plastics, Inc.]
POLYMER CHEMISTRY
A. Molding
B. Casting : for making film. a. Solution casting and melting casting. b. Calendering : thick film.
C. Extrusion : to make rods and pipe.
a. Extruder : screw of injection mold + die instead of mold. b. sometimes to make thin film by extrusion. ex) PE film.
4.2 Fabrication Methods.
POLYMER CHEMISTRY
D. Spinning.
a. melt spinning : for molten polymer.
b. dry spinning
c. wet spinning : solvent soluble polymer.
Fig.4.5 Basic components for spinning.
v
a. Physical blowing agent.
1) Gas : air, nitrogen, carbon dioxide.
2) Low-boiling liquid : pentane, CFC (not to be used now, because of ozone depletion)
b. Chemical blowing agent. 1) Byproduct CO2 for polyurethane synthesis. 2) Decompose on heating and give off nitrogen.
E. Blowing agent : for foamed plastic.
POLYMER CHEMISTRY
A. Molecular weight dependent mechanical properties. a. For vinyl polymer, molecular weight : 105 For polyamide, molecular weight : 20,000 ～ 50,000 b. For small molecular weight, properties of end group : significant In case of high molecular weight : negligible. c. Properties and molecular weight.
4.3 Mechanical Properties
POLYMER CHEMISTRY
Property
Molecular weight
Mechanical
Working range
Nonmechanical
FIGURE 4.6. Dependence of properties on molecular weight (hypothetical polymer).
Viscosity
B. Type of mechanical properties. a. Tensile strength, tensile modulus, elongation. b. Compressive strength : reverse tensile strength. c. Flexural strength : Impact resistance, abrasion resistance, tear resistance, hardness
POLYMER CHEMISTRY
4.3 Mechanical Properties
C. Tensile strength. a. Important and useful mechanical property. 1) Tensile stress : 2) Tensile strain : 3) Tensile modulus : b. Units of tensile strength : 1) CGS : dyne / cm2 2) SI : N / m2 (Pa) 3) pounds per square inch (psi)
=AF
=l
l
E =
c. Unit of modulus same unit of tensile strength. d. Unit of elongation : No dimension.
POLYMER CHEMISTRY
4.3 Mechanical Properties
Stress ()
Brittleplastic
Fiber
Elastomer
Strain ()
FIGURE 4.7. Characteristics of tensile stress-strain behavior.
FIGURE4.8. General tensile stress-strain curve for a typical thermoplastic.
Elongation at break
Elongationat yield
Stress ()
Yieldstress
Strain ()
Ultimatestrength
FIGURE 4.9. Effect of temperature on tensile modulus of an amorphous thermoplastic; log E, modulus scale; Tg, glass transition temperature.
Glassy
Rubbery
Flow
Temperature
log E(N/m2)
Tg3
6
9
D. Temperature dependent mechanical properties a. The modulus of amorphous thermoplastic depend on temperature.
b. Tensile modulus of crystalline and crosslink polymer depend on temperature.
FIGURE 4. 10. Effect of temperature on tensile modulus (log E scale) of various polymers. Tm, crystalline melting temperature. [Reprinted with permission from J. J. Aklonis, J. Chem. Educ., 58, 11 (1981).]
Temperature
log
E (
N/m
2 )
Crystalline
Highlycrosslinked
Lightlycrosslinked
Low molecularweight
Highmolecularweght3
6
9
Tm
E. Time dependent mechanical properties a. viscoelastic property b. creep stress relaxation
F. General relationship between mechanical property and structure. a. Flexible backbone : lower tensile property b. Chain stiffness of backbone or bulky side group : increase tensile property c. Chain stiffness : lower impact strength. cf) Table 4.1 and Table 4.2 d. Tensile strength of fiber Tenacity= N/ tex , tex= gram / 1000meters of the fiber.
4.3 Mechnical Properties
disentanglement by stress like as temperature >
POLYMER CHEMISTRY
TABLE 4.1. Mechanical Properties of Common Homopolymersa
Polymer
Polyethylene, low densityPolyethylene, high densityPolypropylenePoly(vinyl chloride)PolystyrenePoly(methyl methacrylate)Polytetra- fluoroethyleneNylon 66Poly(ethylene terephthalate)Polycarbonate
Strengthb
(Mpa)
8.3-31
22-31
31-4141-5236-5248-76
14-34
76-8348-72
66
Modulusb
(Mpa)
172-283
1070-1090
1170-17202410-41402280-32802240-3240
400-552
-2760-4140
2380
Elongation(%)
100-650
10-1200
100-60040-801.2-2.52-10
200-400
60-30050-300
110
CompressiveStrengthb
(Mpa)
-
20-25
38-5555-9083-90
72-124
12
10376-103
86
FlexuralStrengthb
(Mpa)
-
-
41-5569-11069-10172-131
-
42-11796-124
93
ImpactStrengthc
(N/cm)
No break
0.23-2.3
0.23-0.570.23-1.3
0.20-0.260.17-0.34
1.7
0.46-1.20.14-0.37
9.1
Tensile Properties at BreakProperty
aValues taken from Aranoff,12a converted to SI units, and rounded off.bTo convert megapascals to pounds per square inch, multiply by 145.cIzod notched impact test (see Chap. 5). To convert newtons per centimeter to foot pounds per inch, multiply by 1.75.
TABLE 4.2. Fiber Propertiesa
Fiber Type
Natural Cotton WoolSynthetic Polyester Nylon Aromatic polyamide (aramid)c
Polybenzimidazole Polypropylene Polyethylene (high strength)Inorganicc
Glass Steel
Tenacityb
(N/tex)
0.26-0.440.09-0.15
0.35-0.530.40-0.711.80-2.0
0.270.44-0.792.65d
0.53-0.660.31
SpecificGravity
1.501.30
1.381.141.44
1.430.900.95
2.567.7
aUnless otherwise noted, data taken form L. Rebenfeld, in Encyclopedia of Polymer Science and Engineering (H. f. Mark,N. M. Bikales, C. G. Overberger, G. Menges, and J. I. Kroschwitz, Eds.), Vol. 6, Wiley-Interscience, New York, 1986,pp. 647-733.bTo convert newtons per tex to grams per denier, multiply by 11.3.cKevlar (see Chap. 3, structure 58.)dFrom Chem. Eng. New, 63(8), 7 (1985).eFrom V. L. Erlich, in Encyclopedia of Polymer Science and Technology (H.F. Mark, N. G. Gaylord, and N. M. Bikales, Eds.), Vol. 9, Wiley-Interscience, New Uork, 1968, p. 422.
A. Chemical structure of thermally stable polymer: to have aromatic repeating unit.
TABLE 4.3. Representative Thermally Stable Polymersa
Type
Poly(p-phenylene)
Polybenzimidazole
Polyquinoxaline
Polyoxazole
StructureDecomposition
Temperature (oC)b
660
650
640
620
4.4 Thermal stability
TABLE 4.3. Representative Thermally Stable Polymersa
Type
Polyimide
Poly(phenylene oxide)
Polythiadiazole
Poly(phenylene sulfide)
DecompositionTemperature (oC)b
585c
570
490
490
Structure
aData from Korshak17
bNitrogen atmosphere unless otherwise indicated.cHelium atmosphere. POLYMER CHEMISTRY
a. Thermal stability : to bonds cleavage for degradation b. Poor processability 1) High Tg or high Tm 2) High viscosity of molten polymer 3) Low solubility c. Incorporation of inorganic material. d. Seurcumvent of poor processability 1) Incorporation of flexible chain on backbone or side chain. 2) Insertion of heteroatom. 3) Symmetry→ asymmetry
POLYMER CHEMISTRY
B. Aromatic or cyclic repeating unit
C. Carl S. Marvel: polybenzimidazole fiber
a. Astronaut's space suits and firefighters' protective clothing. b. Cardo polymer (from the Latin cardo, loop) c. Cyclic aromatic groups that lie perpendicular to the planar aromatic backbone. d. Improved solubility with no sacrifice of thermal properties.
NNH NNH
N
N
H
N
N
H
1
POLYMER CHEMISTRY
2
D. Cycloaddition to make cyclic repeating unit.
SCHEME 4.1. Increasing Tg of a polyquinoxaline by intramolecular cycloaddition.
Tg = 265oC
Tg = 215oC
E. Oligomers with reactive End Group.
TABLE 4.4. Some Reactive End Groups for Converting Oligomers to Network Polymers
Type Sturcture
C C
O C N
C CH
N
O
O
N
O
O
CyanateEthynyl
Maleimide
Nadimidea
PhenylethynylaCommon name for 5-norbornene-2,3-dicarboximide.
4.5 Flammability and Flame Resistance.
A. Process of flame propagation. Solid polymer -(heat)→ Depolymerization to monomer(radical formation) → Degradation to combustable gas → Flame formation.
FIGURE 4.11. Representation of polymer combustion. , gas diffusion; , heat flux. [Adapted from Factor.43]
Diffusionzone
Flamefront
Pyrolysiszone
Solidpolymer
B. The object of flame retardation. a. Suppression of smoke and toxic gases. b. Development of nonflammable polymer: self-extinguishing.
C. The strategies of flame resistance. a. Retarding the combustion process in the vapor phase. b. Causing "char" formation in the pyrolysis zone. c. Giving nonflammable gas or cooling the pyrolysis zone.
POLYMER CHEMISTRY
4.5 Flammability and Flame Resistance.
D. Examples of flame resistance. a. Halogen containing polymer: to suppress radical concentration. b. Addition antimony oxide to be formed antimony halide. c. Phosphorus-containing polymers: promotion char. d. Aromatic and network polymers: to promote char. e. Addition Al2O3 · 3H2O to evolve water.
POLYMER CHEMISTRY
4.5 Flammability and Flame Resistance.
A. Types of chemical reaction. a. Free radical reaction by oxygen or UV-light. b. Hydrolysis. c. Ozonolysis.
POLYMER CHEMISTRY
4.6 Chemical Resistance.
B. Preventing hydrolysis.
a. Chemically resistant polyester formulations.
HOCH2C CH CHCH3
CH3CH3
CH3 OH
HOCHCH2O
CH3
C OCH2CHOH
CH3CH3
CH3
7
8 POLYMER CHEMISTRY
4.6 Chemical Resistance.
b. End group blocking.
OH + NCO OCNH
O
CO2H + NCO CNH
O
+ CO2
POLYMER CHEMISTRY
4.6 Chemical Resistance.
B. Preventing hydrolysis.
a. Fluorinated phosphazene.
b. Teflon and copolymer.
N P
Cl
Cl
N P
OCH2CF3
OCH2CF3
CF2CF2 CH2CF2CF2CF CH2CF2
CF3
9 10
11 12 13
POLYMER CHEMISTRY
C. Moisture resistance and chemical inertness: fluorinated polymer.
a. Ozonolysis mechanism.
b. Preventing ozonolysis: to add cyclopentadiene.
CF3
C CO3
C
O O
C
OH2O
C O + CO
14 POLYMER CHEMISTRY
D. Ozonolysis
Monomers containing ultraviolet-absorbing chromophore.
F. Morphology
a. Crystallinity to prevent penetration. b. Crosslinking
POLYMER CHEMISTRY
E. Sunlight protection.
4.6 Chemical Resistance.
O OH
OH15
A. Application for polymer degradability. a. Polymer waste treatment. 1) Photodegradable polymer containing carbonyl functional group. Norrish type II degradation reaction. 2) Biodegradable polymer by microbiology. Poly(α-hydroxybutanoic acid), starch+PE
POLYMER CHEMISTRY
4.7 Degradability
FIGURE 4.12. Schematic of a typical procedure for producing (a) negative resists and (b) positive resists in the manufacture of integrated circuits.
b. Photoresist for IC. 1) Positive resists: radiation promotes degradation of the resist exposed by the mask. 2) Negative resists: radiation makes insoluble network.
A. Application for polymer degradability.
c. Agricultural degradable mulches. 1) Starch-graft-poly(methylacrylate). 2) Block copolymers of amylose or cellulose with polyester.
d. Surgical sutures and implanted polymeric matrix devices.
POLYMER CHEMISTRY
A. Application for polymer degradability.
B. Controlled release: penetration rather than degradation. a. Microencapsulation. b. Strip.
FIGURE 4.13. Membrane-controlled release devices: (a) microencapsulation, and (b) strip.
POLYMER CHEMISTRY
c. 2,4-Dichlorophenoxyacetic acid(2,4-D): herbicide. Vinyl polymer with hydroyzable pendant group, chelate with iron. d. Pheromone release strips: insecticides.
e. Transdermal patches. 1) Nitroglycerin to treat angina. 2) Scopolamine to treat combat motion sickness.
POLYMER CHEMISTRY
B. Controlled release: penetration rather than degradation.
f. Phosphazene polymer. R= amino acids, esters, steroids
g. Poly(N-isopropylacrylamide) 1)
2) To shrink reversibly in response to temperature increase. 3) Incorporation with IPN.
N P
R
R
CH2CH
C NHCH(CH3)2O
POLYMER CHEMISTRY
B. Controlled release: penetration rather than degradation.
A. Classification of electrical conductivity.
a. Insulator : σ < 10-8 S/ cm
b. Semiconductor: 10-7 < σ < 10-1 S/ cm
c. Conductor: σ > 102 S/ cm (σ=conductivity, S (simen)= 1/Ω)
POLYMER CHEMISTRY
4.8 Electrical Conductivity
B. Theory of electrical conductivity for polyacetylene.
a. Soliton.
1) Delocalization regions of conjugated double bond.
2) Extend about 15 bond lengths.
3) Energy gain arising for stabilization.
4) Electron transfer via positive or negative solitons
FIGURE4.14. Proposed conducting unit of polyacetylene. Soliton may be neutral (radical), positive (carbocation), or negative (carbanion).
Soliton
b. Doping: incorporation dopant much as AsF5, I2, Lewis acid, etc.
+ dopant : 1.5×105 S/cm
22 23
2 CH CH[ ] + 3 I2 2 CH CH[ ] +·
+ 2 I3-
CH CH[ ] CH CH[ ] -·
+ Na + Na+
POLYMER CHEMISTRY
B. Theory of electrical conductivity for polyacetylene.
a. Poly(N-vinyl-carbazole) 1) Photoconducting: conduct small degree of electricity under the light. 2) Electrophotography(photocopying)
b. Poly(sulfur nitride): Super conductor
S N 20 POLYMER CHEMISTRY
C. Example of conducting polymers.
19
CH2CH
c. Polyaniline Polypyrrole Polythiophene
Poly(p-phenylene) Poly(p-phenylenevinylene)
d. Conducting polymers to be used as light emitting diode.
(PPV)
NHNH S
CH CH
CH CH
e. Conducting polymers much lower density than metal. polymer=1g/cm3, copper=8.92g/cm3, Gold=19.3g/cm3
24 25 26
27 28
POLYMER CHEMISTRY
C. Example of conducting polymers.
TABLE 4.5. Conductivities of Metals and Doped Polymersa
Material
CopperGoldPolyacetylenePoly(sulfur nitride)Poly(p-phenylene)Poly(p-phenylenevinylene)PolyanilinePolypyrrolePolythiophene
5.8 105
4.1 105
103 – 105
103 – 104
103
103
102 – 103
102 – 103
102
Conductivity (S/cm)b
aData from J. R. Reynolds, A. D. Child, and M. B. Gieselman, in Encyclopedia of Chemical Technology, 4th ed. (J. I. Kroschwitz and M. Howe-Grant, Eds.), Wiley, New York, 1994; and Chem. Eng. News, Jume 22, 1987, p. 20.bI siemen (S) = I ohm-1. POLYMER CHEMISTRY
D. Polyelectrolytes for solid battery.
CH2CH2O P N
(OCH2CH2)2OCH3
(OCH2CH2)2OCH3
29 30
POLYMER CHEMISTRY
4.8 Electrical Conductivity
4.9 Nonlinear Optical Properties
A. Photonics device.
a. Information and image processing.
b. To operate higher rate.
c. To store information much more densely.
POLYMER CHEMISTRY
B. NLO materials a. Inorganic and low molecular weight organic compounds. b. Polymeric materials 1) Conjugated double bond like conducting polymer: Third order harmonic generation. 2) Asymmetric strong dipole aromatic molecule: Second order harmonic generation 3) Containing strong electrowithdrawing and donating group: Second order chromophore.
4) Dipole molecules must be poled at Tg. 5) Stabilizing poled molecule to avoid relaxation.
POLYMER CHEMISTRY
4.9 Nonlinear Optical Properties
CH3CH2
NCH2CH2 CH C C
CN
O
O
N
O
O
CF3
N
O
O
N
N
N
NO2
F3C
31
32
C. Producing NLO polymeric material.
a. Host-Guest combination. Host: matrix polymer. Guest: NLO chromophore.
b. Incorporating chromophore in the polymer backbone or side chain covalently.
POLYMER CHEMISTRY
4.9 Nonlinear Optical Properties
4.10 Additives
A. Purpose of using additives. a. To alter the properties of the polymer. b. to enhance processability.
B. Types of polymer additives.
C. Examples of polymer additives. a. Plasticizer. 1) Internal plasticizer, to have covalent bonds between polymer and plasticizer. 2) External plasticizer, physical mixture with plasticizer.
POLYMER CHEMISTRY
TABLE 4.6. Polymer Additives
Type
Mechanical property modifiers Plasticizers Impact modifiers Reinforcing fillers Nucleating agents
Surface property modifiers Slip and antiblocking agents Lubricants Antistatic agents Coupling agents Wetting agents Antifogging agents
Chemical property modifiers Flame retardants Ultraviolet stabilizers Antioxidants Biocides
Aesthetic property modifiers Dyes and pigments Odorants Deodorants Nucleating agents
Processing modifiers Plasticizers Slip agents and lubricants Low-profile additives Thickening agents
Heat stabilizers Defoaming agents Blowing agents Emulsifiers Crosslinking (curing) agents Promoters
Increase flexibilityImprove impact strengthIncrease strength propertiesModify crystalline morphology
Prevent film and sheet sticking Prevent sticking to machineryPrevent static charge on surfacesImprove bonding between polymer and fillerStabilize dispersions of fillerDisperse moisture droplets on films
Reduce flammabilityImprove light stabilityPrevent oxidative degradationPrevent mildew
Impart colorAdd fragrancePrevent development of odorImprove light transmission
Reduce melt viscosityPrevent sticking to processing machineryPrevent shrinkage and warpageIncrease viscosity of polymer solutions or dispersionsPrevent degradation during processingReduce foamingManufacture stable foamsStabilize polymer emulsionsCrosslink polymerSpeed up crosslinking (curing)
Function
b.
TABLE 4.7. Commonly Used Plasticizers
Aromatic Di-2-ethylhexyl phthalate Di-n-octyl phthalate Di-i-octyl phthalate Di-i-decyl phthalate Di-n-undecyl phthalate Di-n-tridecyl phthalate Tri-2-ethylhexyl trimellitate
Aliphatic Di-2-ethylhexyl adipate Di-2-ethylhexyl sebacate Di-2-ethylhexyl azelate
Epoxy Epoxidized linseed oil Epoxidized soya oil
Polymeric Poly(alkylene adipates, sebacates, or azelates)
Fire retardant Chlorinated paraffins Phosphate esters POLYMER CHEMISTRY
c. Reinforcing material: Composite. 1) Carbon black for tire. 2) Glass fiber for FRP. 3) Aromatic polyamide or graphite fiber for high performance engineering plastic.
POLYMER CHEMISTRY
C. Producing NLO polymeric material.
