79 - STEREOSPECIFIC POLYMERIZATIONS AND CATALYSIS

Abstract

Publisher Summary This chapter focuses on stereospecific polymerizations and catalysis. Two important branches of chemistry, namely, kinetics and catalysis, assume particular aspects when applied to the field of macromolecules. Highly exothermic processes initiated by free radicals have made it possible to produce from simple monomers most of the polymeric macromolecules, having molecular weights of hundreds of thousands, or of millions, which have led to the production of thermoplastic resins on an industrial scale. Stereospecific catalysis is an important process because of its possible applications for several stereo-ordered polymers in the field of plastics. The catalysis makes it possible to investigate a vast new branch of macromolecular chemistry and to produce new classes of linear and highly crystalline polymers, so far unknown. From diolefin monomers, moreover, other crystalline polymers have been obtained in which crystallinity is because of a regular alternation of units having opposite steric configuration. In general, cationic processes yield polymers having low molecular weight, and chemically and sterically irregular structure. This is because of the facility with which chain transfers occur, unless one operates at extremely low temperatures with particular monomers showing certain symmetry (isobutylene). A third polymerization mechanism is given by anionic catalytic processes, which in the past has had a quite negligible importance, if one excludes the production of synthetic rubber by the polymerization of butadiene with sodium as catalyst in Russia before the war.