Alternating Copolymers by Complexed Copolymerization

There have been few studies on how the nature of copolymers is affected by their sequential structure. This is because, in the past, the sequential structure of most copolymers could not be controlled at will. However, such studies have been realized since it was found that alternating sequential regulation can be attained from many monomer combinations, from which only random copolymers had been obtained previously, provided the copolymerization was carried out in the presence of a Lewis acid, such as an alkylaluminum halide. This kind of reaction is termed complexed copolymerization, as distinguished from the conventional alternating copolymerization. Furukawa and coworkers indicated that alternating butadiene—acrylonitrile copolymer is superior in various properties to the corresponding 1:1 random copolymer. Yabumoto and coworkers noticed that 1:1 styrene—acrylonitrile copolymer obtained in the presence of zinc chloride had a higher glass transition temperature than that of the corresponding 1:1 random copolymer made by radical copolymerization. Moreover, the former was hardly colored due to substantial absence of acrylonitrile—acrylonitrile bonds. Thus, it is very interesting how the properties of eopolymers are affected by sequential structure. The present paper describes various properties of alternating copolymers. The first part of this paper introduces a newly developed alternating copolymer of isobutylene and an acrylic ester and compares it with the corresponding homo-polymers. The latter part deals with comparison of alternating and random copolymers. Equimolar copolymers of styrene and acrylonitrile are compared in physical and mechanical properties. Glass transition temperatures of equimolar alternating and random copolymers of various vinyl compounds are compared. An interesting correlation is shown and discussed on the basis of a thermodynamic treatment.