Synthesis and characterization of novel multiarm-star polyisobutylene-polystyrene thermoplastic elastomers

New multiarm-star block copolymers of polyisobutylene (PIB) and polystyrene (PS) were synthesized by living carbocationic polymerization using a novel hexafunctional initiator in conjunction with TiCl4. The new initiator, hex aepoxy squalane (HES) was prepared by a simple epoxidation (RT, 5 min) of c ommercial squalene. The homopolymerization of isobutylene (IB) initiated by HES is living, demonstrated by linear ln([M](o)/[M](t)) vs time and M-n vs conversion plots and relatively narrow molecular weight distributions (MWD = 1.2). The branched nature of the PIBs was proven directly by diphenyl et hylene end capping, and indirectly by kinetic analysis and size exclusion c hromatography (SEC). Subsequent blocking of PIE with PS was demonstrated by triple detection SEC: refractive index (RI), multiangle laser light scater ing (MALLS) and ultraviolet (UV). A new multiarm-star and a conventionally prepared linear triblock copolymer sample were subjected to supercritical f luid (SCF) fractionation and the fractions were analyzed by SEC and H-1 NMR . Analysis of the fractions indicated living conditions for the PS blocking in the star-block. Interestingly, the linear triblock showed bimodal distr ibution in terms of PS content and molecular weight.