Molecular design of polymers

Abstract

This presentation is centred on what the chemist can achieve by control of molecular structure to achieve the ‘simple properties’ in linear, synthetic polymers which make them useful in a modern industrial environment. Transparency is a desirable property, readily accessible with amorphous polymers. Rather special structures are required to produce transparent crystalline polymers in the bulk state. The utility of many polymers is restricted by their susceptibility to chain scission, leading to a drop in molecular weight and hence loss of mechanical strength. A structural approach to defeating this effect is to make ‘ladder’ structures. An approach to the synthesis of novel ladder structures by bi-nuclear regulated copolymerization is suggested. Although copolymerization has been widely studied, little systematic work has been carried out on copolymer systems, which are more difficult to attain, to study the effect of copolymer composition on physical properties. The results are not always those expected, as illustrated by the acrylonitrile/styrene system. An example for further research of this type is proposed. The problems of correlating molecular structure with mechanical properties in any quantitative way are formidable, although much progress has been made on the phenomenological level in the understanding of the physical behaviour of polymers. Attention is drawn to a correlation which has been observed between modulus and certain structural parameters which may open the way to quantitative studies. Toughness is a more difficult property even to define, let alone correlate with structure. Nevertheless qualitative correlations may provide a useful starting point for future research.