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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
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4.1 Introduction 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. POLYMER CHEMISTRY
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4.2 Fabrication Methods. A. Molding
a. Compression molding : thermoset polymer. FIGURE 4.1. Compression molding POLYMER CHEMISTRY
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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
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c. Reaction injection molding (RIM)
FIGURE 4.3. Basic components of a reaction injection molding (RIM) process. [From Modern Plastics Encyclopedia, Reprinted with permission of Modern Plastics.] newly developed molding. polyurethane and other polymer system. POLYMER CHEMISTRY
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A. Molding 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
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4.2 Fabrication Methods. 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. POLYMER CHEMISTRY
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D. Spinning. v a. melt spinning : for molten polymer. b. dry spinning
c. wet spinning : solvent soluble polymer. Fig.4.5 Basic components for spinning.
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E. Blowing agent : for foamed plastic.
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. POLYMER CHEMISTRY
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4.3 Mechanical Properties
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. POLYMER CHEMISTRY
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Property Molecular weight Mechanical Working range Nonmechanical FIGURE 4.6. Dependence of properties on molecular weight (hypothetical polymer). Viscosity
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4.3 Mechanical Properties
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
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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) = A F = l l E = c. Unit of modulus same unit of tensile strength. d. Unit of elongation : No dimension. POLYMER CHEMISTRY
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Fiber Brittle plastic Stress () Elastomer Strain () FIGURE 4.7. Characteristics of tensile stress-strain behavior.
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FIGURE4.8. General tensile stress-strain curve for a typical thermoplastic.
Elongation at break Elongation at yield Stress () Yield stress Strain () Ultimate strength
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D. Temperature dependent mechanical properties
a. The modulus of amorphous thermoplastic depend on temperature. 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) Tg 3 6 9
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b. Tensile modulus of crystalline and crosslink polymer depend on temperature.
FIGURE 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/m2) Crystalline Highly crosslinked Lightly Low molecular weight High weght 3 6 9 Tm
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> 4.3 Mechnical Properties E. Time dependent mechanical properties
a. viscoelastic property b. creep stress relaxation > disentanglement by stress like as temperature 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. POLYMER CHEMISTRY
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aValues taken from Aranoff,12a converted to SI units, and rounded off.
TABLE 4.1. Mechanical Properties of Common Homopolymersa Polymer Polyethylene, low density high density Polypropylene Poly(vinyl chloride) Polystyrene Poly(methyl methacrylate) Polytetra- fluoroethylene Nylon 66 Poly(ethylene terephthalate) Polycarbonate Strengthb (Mpa) 8.3-31 22-31 31-41 41-52 36-52 48-76 14-34 76-83 48-72 66 Modulusb - 2380 Elongation (%) 40-80 2-10 60-300 50-300 110 Compressive 20-25 38-55 55-90 83-90 72-124 12 103 76-103 86 Flexural 41-55 69-110 69-101 72-131 42-117 96-124 93 Impact Strengthc (N/cm) No break 1.7 9.1 Tensile Properties at Break Property 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.
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TABLE 4.2. Fiber Propertiesa
Fiber Type Natural Cotton Wool Synthetic Polyester Nylon Aromatic polyamide (aramid)c Polybenzimidazole Polypropylene Polyethylene (high strength) Inorganicc Glass Steel Tenacityb (N/tex) 0.27 2.65d 0.31 Specific Gravity 1.50 1.30 1.38 1.14 1.44 1.43 0.90 0.95 2.56 7.7 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 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.
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4.4 Thermal stability A. Chemical structure of thermally stable polymer: to have aromatic repeating unit. TABLE 4.3. Representative Thermally Stable Polymersa Decomposition Temperature (oC)b 660 650 640 620 Type Poly(p-phenylene) Polybenzimidazole Polyquinoxaline Polyoxazole Structure
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Decomposition Temperature (oC)b 585c 570 490
TABLE 4.3. Representative Thermally Stable Polymersa Decomposition Temperature (oC)b 585c 570 490 Type Polyimide Poly(phenylene oxide) Polythiadiazole Poly(phenylene sulfide) Structure aData from Korshak17 bNitrogen atmosphere unless otherwise indicated. cHelium atmosphere. POLYMER CHEMISTRY
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B. Aromatic or cyclic repeating unit
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
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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. 1 2 POLYMER CHEMISTRY
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D. Cycloaddition to make cyclic repeating unit.
Tg = 215oC Tg = 265oC SCHEME 4.1. Increasing Tg of a polyquinoxaline by intramolecular cycloaddition.
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E. Oligomers with reactive End Group.
TABLE 4.4. Some Reactive End Groups for Converting Oligomers to Network Polymers Type Sturcture Cyanate Ethynyl Maleimide Nadimidea Phenylethynyl aCommon name for 5-norbornene-2,3-dicarboximide.
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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 Representation of polymer combustion , gas diffusion; , heat flux. [Adapted from Factor.43] Diffusion zone Flame front Pyrolysis Solid polymer
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4.5 Flammability and Flame Resistance.
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
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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
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4.6 Chemical Resistance. A. Types of chemical reaction.
a. Free radical reaction by oxygen or UV-light. b. Hydrolysis. c. Ozonolysis. POLYMER CHEMISTRY
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4.6 Chemical Resistance. B. Preventing hydrolysis.
a. Chemically resistant polyester formulations. 7 8 POLYMER CHEMISTRY
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4.6 Chemical Resistance. B. Preventing hydrolysis.
b. End group blocking. POLYMER CHEMISTRY
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C. Moisture resistance and chemical inertness: fluorinated polymer.
a. Fluorinated phosphazene. 9 10 b. Teflon and copolymer. 11 12 13 POLYMER CHEMISTRY
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D. Ozonolysis a. Ozonolysis mechanism.
a. Ozonolysis mechanism. b. Preventing ozonolysis: to add cyclopentadiene. 14 POLYMER CHEMISTRY
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4.6 Chemical Resistance. E. Sunlight protection. F. Morphology
Monomers containing ultraviolet-absorbing chromophore. 15 F. Morphology a. Crystallinity to prevent penetration. b. Crosslinking POLYMER CHEMISTRY
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4.7 Degradability 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
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A. Application for polymer degradability.
b. Photoresist for IC. 1) Positive resists: radiation promotes degradation of the resist exposed by the mask. 2) Negative resists: radiation makes insoluble network. FIGURE Schematic of a typical procedure for producing (a) negative resists and (b) positive resists in the manufacture of integrated circuits.
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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
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B. Controlled release: penetration rather than degradation.
a. Microencapsulation. b. Strip. FIGURE Membrane-controlled release devices: (a) microencapsulation, and (b) strip. POLYMER CHEMISTRY
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B. Controlled release: penetration rather than degradation.
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
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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. POLYMER CHEMISTRY
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4.8 Electrical Conductivity
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
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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
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B. Theory of electrical conductivity for polyacetylene.
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 I3- - + Na + Na+ POLYMER CHEMISTRY
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C. Example of conducting polymers.
a. Poly(N-vinyl-carbazole) 1) Photoconducting: conduct small degree of electricity under the light. 2) Electrophotography(photocopying) 19 b. Poly(sulfur nitride): Super conductor 20 POLYMER CHEMISTRY
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C. Example of conducting polymers.
c. Polyaniline Polypyrrole Polythiophene Poly(p-phenylene) Poly(p-phenylenevinylene) d. Conducting polymers to be used as light emitting diode. (PPV) C. Example of conducting polymers. 24 25 26 28 27 e. Conducting polymers much lower density than metal. polymer=1g/cm3, copper=8.92g/cm3, Gold=19.3g/cm3 POLYMER CHEMISTRY
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Poly(p-phenylenevinylene) Polyaniline Polypyrrole Polythiophene
TABLE 4.5. Conductivities of Metals and Doped Polymersa Material Copper Gold Polyacetylene Poly(sulfur nitride) Poly(p-phenylene) Poly(p-phenylenevinylene) Polyaniline Polypyrrole Polythiophene 5.8 105 4.1 105 103 – 105 103 – 104 103 102 – 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
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4.8 Electrical Conductivity
D. Polyelectrolytes for solid battery. 30 29 POLYMER CHEMISTRY
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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
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4.9 Nonlinear Optical Properties
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
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4.9 Nonlinear Optical Properties
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
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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
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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 Processing modifiers Slip agents and lubricants Low-profile additives Thickening agents Heat stabilizers Defoaming agents Blowing agents Emulsifiers Crosslinking (curing) agents Promoters Increase flexibility Improve impact strength Increase strength properties Modify crystalline morphology Prevent film and sheet sticking Prevent sticking to machinery Prevent static charge on surfaces Improve bonding between polymer and filler Stabilize dispersions of filler Disperse moisture droplets on films Reduce flammability Improve light stability Prevent oxidative degradation Prevent mildew Impart color Add fragrance Prevent development of odor Improve light transmission Reduce melt viscosity Prevent sticking to processing machinery Prevent shrinkage and warpage Increase viscosity of polymer solutions or dispersions Prevent degradation during processing Reduce foaming Manufacture stable foams Stabilize polymer emulsions Crosslink polymer Speed up crosslinking (curing) Function
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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 b. POLYMER CHEMISTRY
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C. Producing NLO polymeric material.
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
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