Classification of Polymers

What is a polymer?

Imagine life without plastic buckets, synthetic clothes, tyres, toys, and electrical insulation — this whole family of materials exists because of polymers, and they form the backbone of four major industries: plastics, elastomers, fibres, and paints & varnishes.

The name itself tells the story: it comes from the Greek poly (many) and mer (part/unit). A polymer is a very large molecule (a macromolecule) with a high molecular mass, typically in the range 10³ to 10⁷ u. It is built by joining together many small, repeating structural units.

• The small, reactive starting molecules are called monomers.
• The repeating units in the polymer are derived from these monomers and are held together by covalent bonds.
• The reaction that links monomers into a polymer is called polymerisation.

Classifying polymers by source

One of the simplest ways to classify polymers is by where they come from. This gives three groups:

• Natural polymers — occur in plants and animals, e.g. proteins, cellulose, starch, natural resins, and rubber.
• Semi-synthetic polymers — made by chemically modifying a natural polymer, e.g. cellulose acetate (rayon) and cellulose nitrate, both derived from cellulose.
• Synthetic polymers — entirely man-made, e.g. polythene (a plastic), nylon 6,6 (a synthetic fibre), and Buna-S (a synthetic rubber). These are used extensively in both daily life and industry.

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Polymers can also be classified in other ways — by their structure, by the intermolecular forces holding their chains together, or by their mode of polymerisation (how the monomers actually combine). These alternative classifications are developed in the sections that follow.