2 INTRODUCTIONNatural Polymers Leather, wood, rubber, cellulose, cotton, wool.Synthetic polymers Synthesized from small organic molecules.CHEMISTRY OF POLYMER MOLECULESHydrocarbons (many organic materials)= composed of hydrogen and carbonCovalent BondingH-C-HHMethaneEthyleneSimilarly
3 POLYMERISATIONMers = small structural entities making up the ‘poly’mer.Ethylene(C2H4) gasCAN BE CONVERTED TO POLYETHYLENE(PE) SolidCatalystbonding unsatisfied for this C atombonding satisfied for C atom
7 MOLECULAR WEIGHT Number average Weight-average Not all chains same lengthWeight-average
8 For copolymersDegree of polymerizationMolecular weight of mer j
9 Branched Linear Crosslinked Network e.g. Polyethylene, Nylon Lower densityCrosslinkedNetworke.g. Rubbere.g. Epoxy
10 HOMOPOLYMERS COPOLYMERS Polymers composed of two or more different ‘mer’ unitsBifunctional, trifunctional mers
11 Styrene-butadiene rubber (SBR) random copolymer Used in automobile tires.
12 POLYMER CRYSTALLINITY = Packing of molecular chains so as to produce an ordered atomic array.Small molecules (Methane, H2O) either either totally crystalline (as solids)or amorphous (as liquids)However POLYMERS only partially crystalline (semi-crystalline)Max. crystallinity ~ 95%.
13 Properties greatly affected by degree of crystallinity (crystalline = stronger and more resistant tosoftening by heat. important to quantify degree crystallinityCrystalline polymer = higher density
14 Slower cooling rates from the melt favor higher crytallinity (giving time for ordered configurations)Linear Polymers Crystallization easily accomplished, since no restriction tochain alignmentBranched polymers NEVER highly crystallineSide branches interfere with crystallizationNetwork Polymers AMORPHOUSCOPOLYMERSMore Irregular and random mer less crystallinityAlternating and block copolymers likelihood of crystallization.Random and Graft copolymers Normally Amorphous