MSE 383, Unit 1-4. Joshua U. Otaigbe Iowa State University Materials Science & Engineering Dept.

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1 Polymer Classifications Mole. Wt. MSE 383, Unit 1-4 Joshua U. Otaigbe Iowa State University Materials Science & Engineering Dept. Introduction Recall polymer (macromolecular) definition Covalent linkages of many repeating monomer units (polymer or chain molecules or polymer chains) very high MW (e.g., MW or PS = 300,000 (cf. MW of small molecules)) Chemical properties defined by monomer properties Physical properties are UNIQUE and changeable (large size, interactions, chain flexibility, M = xmo). Degree of Polymerization D.P. = polymer chain length (# repeating units) e.g., D.P. (PVC) = 1000 M(PVC) = xmo = 1000 x 62.5 x (or D.P.) is more convenient than MW for polymers 1000 < MW < 1,000,000 (typical values) 10 < n, x, D.P. < 10,000 (where M o 100) 1.4.1

2 Class Practice Problem If a particular type of PE has a degree of polymerization of 10,000, what is its molecular weight? (atomic masses of C and H are 12 & 1) Molecular vs. Microstructural Engineering Different properties by joining monomers in different ways (cf. METALS) >> cf: Metals can only be heat-treated or work-treated but their molecules (& crystals) are fixed forever (microstructural engineering) >> Microstructural eng. also possible with polymer (structure-property relations to be discussed later) ILLUSTRATE a) polyethylene c) rubber (x-linked) d) Bakelite Epoxies Molecular Classifications USAGE plastics, rubber, fiber, coatings & films POLYMERIZATION ROUTES condensation vs. addition (or step vs. chain) copolymerization (alternating, random, block, graft) NATURAL vs. SYNTHETIC ** silk, wool, DNA, cellulose 1.4.2

3 Molecular Classifications, Cont d 1. USAGE ARCHITECTURE FINITE thermoplastics, may be linear or branched INFINITE thermosets, usually crosslinked def. - serves to introduce concepts of chemical structure and terminology [poly (name of momoner)] PLASTICS (pure polymers + additives ** ) >> traditionally excludes rubber (NOT synonymous with polymers) >> e.g., PE, PS, PVC Chemical Structures of Some Common Polymers 1.4.3

4 Chemical Structures of Some Common Polymers, Cont d 1.4.4

5 Examples of Plastics Usage, Cont d Plastics (pure polymers + additives**) cont d >> construction, packaging, automobiles, furniture, dishware, etc. ELASTOMERS/SYNTHETIC RUBBERS >> emphasize double bond reactivity >> PBD, PlsoP (natural), PCP (neoprene), SBR >> tires & tire products, gaskets, seals, etc. FIBERS (explain high strength & stiffness ** ) >> Nylon or PA; Polyester (PET); Rayon (modified cellulose ** ) >> Clothing, upholstery, etc. COATINGS & FILMS (many types) >> paints, structural adhesives, HMPSA s, varnish, lacquers - typically polymer emulsions Emphasize complex structure of polymers/benefits (fortuitously, polymers can be used without in-depth knowledge of structure) Additional Reading (chap. 1, Rodriguez, 1989) (importance & other e.g.s) 2. Polymerization Routes 2 broad classifications (chain vs. step) W.J. Carothers et al. >> ADDITION (or Chain ) chain reactions involving an unpaired electron or an ion common with DOUBLE-BONDED compounds, e.g., PE 1.4.5

6 Addition Reaction 2. Polymerization Routes, Cont d >> CONDENSATION (or step ) reaction between TWO polyfunctional molecules (cf. condensation reactions of lower MW materials) Example of Condensation Rxn ethylene glycol + terephathalic acid bifunctional product + water Linear PET >> chain or step used to produce linear & branched polymers Condensation Reaction 2. Polymerization Routes, Cont d COPOLYMERIZATION (A, B or C) >> EMPHASIZE technological importance >> SBR, LIPS, HIPS, etc. >> Alternating >> Random >> Block >> Graft Alternating monomers 1.4.6

* ) Animal sources >> silk, wool, chemically known as proteins Human tissues >> muscle fiber, living organisms (DNA, RNA) Bond

7 3. Natural vs. Synthetic Plant sources >> cellulosic fibers (linen, jute, hemp), corn starch ** >> soy protein ** (Emphasize biodegradability * ) Animal sources >> silk, wool, chemically known as proteins Human tissues >> muscle fiber, living organisms (DNA, RNA) Bond Rotation Fixed bonds angles (109 28') & random chain conformations ILLUSTRATE >> random conformation of carbon backbone Chain Entaglement >> Note bending, kinking, coiling (real case) >> reptational motions overhead Stereoisomerism 1.4.7

8 cf. Spaghetti Crystalline vs. Amorphous (Unit 2) * End of Lecture READ Chaps 1, 2, Class text 1.4.8

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