Synthesis and Characterization of Novel Multiarm-Star Polyisobutylene-Polystyrene Thermoplastic Elastomers

Abstract

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, hexaepoxy squalane (HES) was prepared by a simple epoxidation (RT, 5 min) of commercial squalene. The homopolymerization of isobutylene (IB) initiated by HES is living, demonstrated by linear ln([M]o/[M]t) vs time and Mn vs conversion plots and relatively narrow molecular weight distributions (MWD=1.2). The branched nature of the PIBs was proven directly by diphenyl ethylene end capping, and indirectly by kinetic analysis and size exclusion chromatography (SEC). Subsequent blocking of PIB with PS was demonstrated by triple detection SEC: refractive index (RI), multiangle laser light scatering (MALLS) and ultraviolet (UV). A new multiarm-star and a conventionally prepared linear triblock copolymer sample were subjected to supercritical fluid (SCF) fractionation and the fractions were analyzed by SEC and 1H NMR. Analysis of the fractions indicated living conditions for the PS blocking in the star-block. Interestingly, the linear triblock showed bimodal distribution in terms of PS content and molecular weight.