What a polymer is

Look at the pictures in figure 14.3: plastic ware, clothes and toys that we use every day. What is the chemical nature of these materials?

At the level of their molecules they share a special feature: they are all made of very large molecules built as long chains. Many of these long-chain molecules are also made of small molecular units repeated over and over. So the molecules that make up these materials are called polymers.

Look at the chain made by linking paper clips in figure 14.4. Each single paper clip can be thought of as a monomer and the chain of clips as a polymer. The basic structural units the chain contains after the polymer has formed are called repeating units.

Monomers have a relatively small molecular mass. But polymers, formed by the polymerisation of a large number of monomers, have very high relative molecular masses.

Why the paper clips are a good model

Each paper clip is a complete object on its own, like a monomer molecule. Joined end to end, they make something with new properties — a chain you can wrap round a box — though every link is still the same clip. A polythene molecule may contain thousands of units, so its mass is thousands of times that of one monomer. That great length is where polymers get their strength and flexibility: long chains tangle together like cooked noodles and are hard to pull apart.