ABSTRACT
Homopolymers of conjugated dienes such as 1,3-butadiene, isoprene, chloroprene, and other alkylsubstituted 1,3-butadienes, as well as copolymerzs with styrene and acrylonitrile, are of great economical importance [1-3]. The conjugated dienes can polymerize via 1,4 or 1,2 linkage of monomeric units. In addition to this, 3,4 linkage occurs with butadienes bearing substituents in the 2-position. In the case of 1,4 linkage the polymer chain can exist as cis or trans type:
ð13Þ
1,2 Linkage yields a tertiary carbon atom, thereby making it possible to form isotactic, syndiotactic, and atactic polybutadiene (3), in analogy to polypropene. The rare 3,4 linkage also gives isotactic, syndiotactic, or atactic configuration. This applies only to high stereoselectivities. Further isomeric structures are formed when next to head-to-tail linkages; head-to-head and tail-to-tail linkages also occur. The polymerization of dienes can be initiated ionically by coordination catalysts or by radicals [4-10].
