Polymers

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A polymer is a high molecular mass molecule formed by linking up of two or more small molecules called monomers. Example: Polyethene –(–CH₂–CH₂–)ₙ– is a polymer of ethene monomer (CH₂=CH₂).

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Homopolymer: Formed from only one kind of monomer. Example: Polyethene from ethene. Copolymer: Formed from more than one kind of monomer. Example: Buna-S rubber from 1,3-butadiene and styrene.

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Addition polymerization involves addition of monomer units to form a growing chain. Steps: 1) Initiation - Free radicals formed by catalyst, 2) Chain propagation - Free radicals attack monomers formin

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Condensation polymerization involves combination of monomers with elimination of small molecules like H₂O, HCl, NH₃. Example: Nylon-66 formation: nH₂N-(CH₂)₆-NH₂ + nHOOC-(CH₂)₄-COOH → [-NH-(CH₂)₆-NHCO

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Addition: 1) Involves unsaturated monomers, 2) Fast reaction, 3) No small molecules eliminated. Condensation: 1) Involves bifunctional monomers, 2) Step-wise slow reaction, 3) Small molecules like H₂O

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1) Natural Polymers: Obtained from nature. Examples: Starch, cellulose, natural rubber, proteins. 2) Synthetic Polymers: Prepared in laboratories (man-made). Examples: Polyethene, PVC, nylon, teflon,

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Elastomers are polymers with weak van der Waals forces between chains. Properties: Easily stretched on small stress, regain original shape when stress removed, have few cross-links. Example: Natural r

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Thermoplastic: Linear polymers, weak intermolecular forces, soften on heating, can be remolded. Examples: PVC, polystyrene. Thermosetting: Cross-linked polymers, strong chemical bonds, do not melt on