Basic definitions and nomenclature

Several important terms and concepts must be understood in order to discuss fully the synthesis, characterization, structure and properties of polymers. Most of these will be defined and discussed in detail in subsequent chapters. However, some are of such fundamental importance that they must be defined at the outset. 

In strict terms, a polymer is a substance composed of molecules which have long sequences of one or more species of atoms or groups of atoms linked to each other by primary, usually covalent, bonds. The emphasis upon substance in this definition is to highlight that although the words polymer and macromolecule are used interchangeably, the latter strictly defines the molecules of which the former is composed. 

Macromolecules are formed by linking together monomer molecules through chemical reactions, the process by which this is achieved being known as polymerization. For example, polymerization of ethylene yields polyethylene, a typical sample of which may contain molecules with 50000 carbon atoms linked together in a chain. It is this long chain nature which sets polymers apart from other materials and gives rise to their characteristic properties. 

The definition of macromolecules presented up to this point implies that they have a linear skeletal structure which may be represented by a chain with two ends. Whilst this is true for many macromolecules, there are also many with non-linear skeletal structures of the type shown in Fig. 1.1. 

Branched polymers have side chains, or branches, of significant length which are bonded to the main chain at branch points (also known as 

In the discussion of the structure and properties of polymers there are several important words and concepts used which need to be defined. Most of these are discussed in detail when they are introduced, but at this stage there are several terms that must be defined. 

A polymer is a long molecule which contains a chain of atoms held 

If only one type of monomer is employed to form the polymer the resulting molecule is called a homopolymer. Often superior properties are obtained by using different types of monomer species. In this case the polymer is termed a copolymer. 

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