Both polythene (left) and polyamide (right) are examples of polymers, which are large molecules formed from chains of repeating simple molecular sub-units known as monomers. Polythene (polyethylene), for example, is a long chain of individual molecules of ethene (C2H4) joined together. Polymerisation occurs when monomers are subjected to conditions of heat and presure, usually in the presence of a catalyst. The majority of synthetic polymers are plastics. These models formed part of an interactive display at the Science Museum, London, demonstrating the difference in stiffnes between these two plastics.
© Science Museum / Science & Society Picture Library