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Chapter 4. Chemical Structure and Polymer Properties

POLYMER CHEMISTRY . 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

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Chapter 4. Chemical Structure and Polymer Properties

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  1. POLYMER CHEMISTRY 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

  2. POLYMER CHEMISTRY 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.

  3. FIGURE 4.1. Compression molding POLYMER CHEMISTRY 4.2 Fabrication Methods. A. Molding a. Compression molding : thermoset polymer.

  4. FIGURE 4.2. Injection molding. [Reprinted from V. Hopp and I. Hennig, Handbook of Industrial Chemistry, copyright 1938, courtesy of McGraw-Hill.] POLYMER CHEMISTRY b. Injection molding : thermoplastic polymer.

  5. FIGURE 4.3. Basic components of a reaction injection molding (RIM) process. [From Modern Plastics Encyclopedia, 1984-85. Reprinted with permission of Modern Plastics.] POLYMER CHEMISTRY c. Reaction injection molding (RIM) newly developed molding.    polyurethane and other polymer system.

  6. FIGURE 4.4. Blow molding. [Courtesy of the Society of the Plastics, Inc.] POLYMER CHEMISTRY A. Molding d. Reinforced reaction injection mold (RRIM) : Modified RIM for fiber reinforcement. e. Blow molding : for bottles.

  7. POLYMER CHEMISTRY 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.

  8. 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.

  9. POLYMER CHEMISTRY 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.

  10. POLYMER CHEMISTRY 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.

  11. Property Viscosity Working range Molecular weight Nonmechanical Mechanical FIGURE 4.6. Dependence of properties on molecular weight (hypothetical polymer).

  12. POLYMER CHEMISTRY 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

  13. F  = l  = A l  E =  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) c. Unit of modulus same unit of tensile strength. d. Unit of elongation :No dimension.

  14. Fiber Brittle plastic Stress () Elastomer Strain () FIGURE 4.7. Characteristics of tensile stress-strain behavior.

  15. Elongation at break Elongation at yield Stress () Yield stress Strain () Ultimate strength FIGURE4.8. General tensile stress-strain curve for a typical thermoplastic.

  16. Glassy 9 Rubbery log E (N/m2) 6 Flow Tg 3 Temperature FIGURE 4.9. Effect of temperature on tensile modulus of an amorphous thermoplastic; log E, modulus scale; Tg, glass transition temperature. D. Temperature dependent mechanical properties a. The modulus of amorphous thermoplastic depend on temperature.

  17. Crystalline 9 Highly crosslinked log E (N/m2) 6 Lightly crosslinked Low molecular weight High molecular weght 3 Tm 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).]  b. Tensile modulus of crystalline and crosslink polymer depend on temperature.

  18. POLYMER CHEMISTRY 4.3 Mechnical Properties E. Time dependent mechanical properties a. viscoelastic property        b. creep stress relaxation    > disentanglement by stress like astemperature 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.

  19. TABLE 4.1. Mechanical Properties of Common Homopolymersa Impact Strengthc (N/cm) No break 0.23-2.3 0.23-0.57 0.23-1.3 0.20-0.26 0.17-0.34 1.7 0.46-1.2 0.14-0.37 9.1 Compressive Strengthb (Mpa) - 20-25 38-55 55-90 83-90 72-124 12 103 76-103 86 Flexural Strengthb (Mpa) - - 41-55 69-110 69-101 72-131 - 42-117 96-124 93 Tensile Properties at Break Property Modulusb (Mpa) 172-283 1070-1090 1170-1720 2410-4140 2280-3280 2240-3240 400-552 - 2760-4140 2380 Elongation (%) 100-650 10-1200 100-600 40-80 1.2-2.5 2-10 200-400 60-300 50-300 110 Strengthb (Mpa) 8.3-31 22-31 31-41 41-52 36-52 48-76 14-34 76-83 48-72 66 Polymer Polyethylene, low density Polyethylene, high density Polypropylene Poly(vinyl chloride) Polystyrene Poly(methyl methacrylate) Polytetra- fluoroethylene Nylon 66 Poly(ethylene terephthalate) Polycarbonate 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.

  20. TABLE 4.2. Fiber Propertiesa Specific Gravity 1.50 1.30 1.38 1.14 1.44 1.43 0.90 0.95 2.56 7.7 Tenacityb (N/tex) 0.26-0.44 0.09-0.15 0.35-0.53 0.40-0.71 1.80-2.0 0.27 0.44-0.79 2.65d 0.53-0.66 0.31 Fiber Type Natural Cotton Wool Synthetic Polyester Nylon Aromatic polyamide (aramid)c Polybenzimidazole Polypropylene Polyethylene (high strength) Inorganicc Glass Steel 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.

  21. 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

  22. POLYMER CHEMISTRY TABLE 4.3. Representative Thermally Stable Polymersa Decomposition Temperature (oC)b 585c 570 490 490 Type Polyimide Poly(phenylene oxide) Polythiadiazole Poly(phenylene sulfide) Structure aData from Korshak17 bNitrogen atmosphere unless otherwise indicated. cHelium atmosphere.

  23. POLYMER CHEMISTRY B. Aromatic or cyclic repeating unit a. Thermal stability : to bonds cleavage for degradation b. Poor processability 1) High Tgor 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

  24. POLYMER CHEMISTRY 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

  25. D. Cycloaddition to make cyclic repeating unit. Tg= 215oC Tg= 265oC SCHEME 4.1. Increasing Tg of a polyquinoxaline by intramolecular cycloaddition.

  26. 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. E. Oligomers with reactive End Group.

  27. Diffusion zone Solid polymer Flame front Pyrolysis zone FIGURE 4.11. Representation of polymer combustion. , gas diffusion; , heat flux. [Adapted from Factor.43] 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.

  28. POLYMER CHEMISTRY 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.

  29. 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.

  30. POLYMER CHEMISTRY 4.6 Chemical Resistance. A. Types of chemical reaction. a. Free radical reaction by oxygen or UV-light. b. Hydrolysis. c. Ozonolysis.

  31. 7 8 POLYMER CHEMISTRY 4.6 Chemical Resistance. B. Preventing hydrolysis. a. Chemically resistant polyester formulations.

  32. POLYMER CHEMISTRY 4.6 Chemical Resistance. B. Preventing hydrolysis. b. End group blocking.

  33. POLYMER CHEMISTRY C. Moisture resistance and chemical inertness: fluorinated polymer.  a. Fluorinated phosphazene. 9 10 b. Teflon and copolymer. 13 11 12

  34. 14 POLYMER CHEMISTRY D. Ozonolysis a. Ozonolysis mechanism. b. Preventing ozonolysis: to add cyclopentadiene.

  35. POLYMER CHEMISTRY 4.6 Chemical Resistance. E. Sunlight protection.  Monomers containing ultraviolet-absorbing chromophore. 15 F. Morphology a. Crystallinity                        to prevent penetration.   b. Crosslinking

  36. POLYMER CHEMISTRY 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

  37. 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 4.12. Schematic of a typical procedure for producing (a) negative resists and (b) positive resists in the manufacture of integrated circuits.

  38. POLYMER CHEMISTRY 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.

  39. POLYMER CHEMISTRY B. Controlled release: penetration rather than degradation. a. Microencapsulation. b. Strip. FIGURE 4.13. Membrane-controlled release devices: (a) microencapsulation, and (b) strip.

  40. POLYMER CHEMISTRY 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.

  41. 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 B. Controlled release: penetration rather than degradation.

  42. POLYMER CHEMISTRY 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)

  43. Soliton FIGURE4.14. Proposed conducting unit of polyacetylene. Soliton may be neutral (radical), positive (carbocation), or negative (carbanion). 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

  44. ] ] [ [ 2 + 2 I3- CH CH + 3 I2 2 CH CH · + ] + Na [ CH CH ] + Na+ [ CH CH · - 23 22 POLYMER CHEMISTRY B. Theory of electrical conductivity for polyacetylene. b. Doping: incorporation dopant much as AsF5, I2, Lewis acid, etc.  + dopant : 1.5×105 S/cm

  45. 19 POLYMER CHEMISTRY   C. Example of conducting polymers.  a. Poly(N-vinyl-carbazole) 1) Photoconducting: conduct small degree of      electricity under the light.  2) Electrophotography(photocopying)  b. Poly(sulfur nitride): Super conductor 20

  46. c. Polyaniline          Polypyrrole         Polythiophene   Poly(p-phenylene)      Poly(p-phenylenevinylene) d. Conducting polymers to be used as light emitting diode.  (PPV) POLYMER CHEMISTRY   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

  47. TABLE 4.5. Conductivities of Metals and Doped Polymersa 5.8  105 4.1  105 103– 105 103 – 104 103 103 102– 103 102 – 103 102 Material Copper Gold Polyacetylene Poly(sulfur nitride) Poly(p-phenylene) Poly(p-phenylenevinylene) Polyaniline Polypyrrole Polythiophene 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

  48. POLYMER CHEMISTRY 4.8 Electrical Conductivity D. Polyelectrolytes for solid battery. 30 29

  49. POLYMER CHEMISTRY 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.

  50. 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

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