Polymers

Abstract

From the chemical point of view, polymers comprise long molecules in which the same basic unit is replaced many times. Polyvinyl chloride, P.V.C., a typical polymer consists of vinyl chloride units linked together. Polymers occur widely in nature. In the inorganic world, rocks, clays and sands are all polymers based on units containing silicon and oxygen. In the organic realm, the structural materials of living organisms are polymers: cellulose in plants and proteins in animals. The products of metabolism of plants and animals may also be polymeric. One important example is natural rubber - a long chain of isoprene units. In physical properties most polymers fall into one of the three classes - plastics, rubbers and fibres. Some polymeric materials can be stretched to many times their initial length, yet on releasing return to their original dimensions. These are called rubbers. Plastics cannot be reversibly deformed in this manner, and are often hard and glassy. Nylon and other high polymers are characterised by marked readiness to form fibres strong along their length but often weak laterally. Such man-made fibres can be spun woven or knitted into fabrics.