16.12: Summary

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Polymers can be synthesised artificially from one or more type of monomers by chain growth or step growth polymerisation, or found in nature. Their names usually involve the name of the monomer(s) from which they were made.

A polymer has a fixed configuration, but may change its shape by conformation changes – rotations around C-C bonds. The polymer may be modelled as a freely jointed chain of segments, each measuring one Kuhn length. The root-mean end-to-end distance of a random walk is given by ln^½.

Physical properties depend on structure:

light cross-linking produces an elastomer,
heavy cross-linking a thermoset and
no cross-links a thermoplastic.

Properties also depend on crystallinity. The degree of crystallinity is controlled by the regularity of its structure, for example stereoregularity (isotactic, syndiotactic or atactic) and the amount of branching.

Synthesis produces a distribution of molecular weights, which have a number average and a weight average. Identification tests can be carried out with freely available materials.

These are the basics of polymer science and will allow you to move on to other polymer TLPs.

Going further

The following DoITPoMS TLPs cover more advanced topics relating to polymers and will provide lots of further reading. They are listed in an approximate decreasing order of relevance.

Crystallinity in polymers

The Glass Transition in Polymers

The Stiffness of Rubber

Examination of an artefact

Introduction to photoelasticity

Elasticity in biological materials