2.3 Chain configuration
The structure of repeat units is fixed by the chemical bonds between adjacent atoms. The shape or shapes thus created is known as the configuration, and for chains will be the chain configuration. Like children's plastic building blocks, however, there can be many different configurations for a given set of atoms of a particular type. The different structures which have identical chemical formulae are known as isomers, and such isomers can have quite different properties. Isomerism becomes an important structural feature as the complexity of molecules increases, and is thus very important for long polymer chains. There are various types of isomerism of especial interest for polymers, all essentially based on the nature of the carbon bond and the way carbon bonds are oriented in space.