Developments in polymerization

Abstract

The foundations for the understanding of the major mechanisms of polymer synthesis, that is, radical, anionic, cationic and coordination addition polymerizations, and stepwise condensation and rearrangement polymerizations, were laid during the period from 1930 to 1960. Of the mechanisms mentioned above, which we can regard as being the primary methods for the synthesis of polymers, the most recently discovered is coordination (or Ziegler-Natta) polymerization.1 Today, literally hundreds of different types of polymers are produced by these mechanisms, ranging from bulk thermoplastics such as polyethylene, polystyrene and polyvinyl chloride), through fibre-forming materials such as polyacrylonitrile, polyesters and polyamides (nylons), elastomers such as cis-1,4-polyisoprene, polychloroprene and ethylene-propylene copolymers, to high-performance engineering materials such as polycarbonates, epoxy resins, polyimides and aromatic polyethers and polysulphones. Much of the research and development in polymer synthesis over the past thirty years has been concerned with improvements to, and refinements of, the above primary methods aimed at achieving one or more of the following objectives: 1. the better control of polymer molecular weight and molecular weight distribution; 2. the better control of polymer microstructure, i.e. stereoisomerism, geometrical isomerism, regioisomerism and, in the case of copolymers, also composition and monomer sequence distribution; and 3. the generation of polymers based on new monomers and hence of polymers with new properties and new applications.