5 - Styrenic Block Copolymers

Abstract

Styrenic block copolymers (SBCs) are based on simple molecules of the ABA type, where A is the hard (polystyrene) segment and B a polydiene (polybutadiene or polyisoprene) soft segment. Other SBCs are produced by the hydrogenation of the base SBS and SIS block copolymers. The base polymers are produced by anionic polymerization in which the segments (blocks) are formed by a reaction initiated by an organolithium initiator. The techniques applied are sequential, coupling, and multifunctional initiation. The morphology of the SBCs is based on the polystyrene blocks, which are hard, and the elastomeric blocks, which are soft. The hard blocks are forming physical thermoreversible cross-links. The styrenic block copolymers of the styrene-isobutylene-styrene (SIBS) are produced by the carbocationic reaction. By the use of multifunctional initiators in this reaction, it is possible to synthesize multiarm star and arborescent (tree-like) block copolymers. Recent commercial development includes highly branched star copolymers, high-molecular-weight SBCs, low-styrene SBCs, and more.