Polymers

Lesson

Part 1 — giant molecules built from small repeating units. (Formative assessment only; not in the board exam.)

In this lesson you will

Define polymer, monomer, repeating unit and degree of polymerisation
Classify polymers by source, structure, mode of polymerisation and molecular forces
Distinguish addition and condensation polymerisation, and homopolymers and copolymers
Explain free radical addition polymerisation

Table of everyday items and the polymers they are made of
Everyday item	Polymer
Carry bag	Polythene
Non-stick pan coating	Teflon
Toothbrush bristles, ropes	Nylon
Saree, shirt fabric	Terylene (polyester)
Switch, plug	Bakelite
Car tyre	Vulcanised rubber, Buna-S

Concept

Monomers, polymers and repeating units

A polymer is a very large molecule (molar mass about 10³–10⁷ g mol⁻¹) made of many repeating structural units derived from small molecules called monomers. The process is polymerisation. The number of repeating units in a chain is the degree of polymerisation.

n\,\mathrm{CH_2{=}CH_2} \rightarrow \mathrm{-\!\!\left(CH_2-CH_2\right)\!\!-}_{n}

Table of polymers with their monomers and repeating units
Polymer	Monomer	Repeating unit
Polythene	CH₂=CH₂	–CH₂–CH₂–
PVC	CH₂=CHCl	–CH₂–CHCl–
Teflon	CF₂=CF₂	–CF₂–CF₂–
Polyacrylonitrile	CH₂=CHCN	–CH₂–CH(CN)–

Concept

Classification by source and structure

By source: natural (proteins, cellulose, starch, natural rubber), semi-synthetic (cellulose acetate, cellulose nitrate, vulcanised rubber), synthetic (polythene, nylon, Buna-S). By structure: linear, branched-chain and cross-linked (network).

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