Synthesis and crystallization behavior study of syndiotactic polystyrene-g -isotactic polypropylene (sPS-g -iPP) graft copolymers

Abstract

Based on coordination polymerization mechanism only, novel stereoregular graft copolymers with syndiotactic polystyrene main chain and isotactic polypropylene side chain (sPS-g-iPP) were synthesized via two steps of catalytic reactions. First, a chain transfer reaction was initiated by a chain transfer complex composed of a styrene derivative, 1,2-bis(4-vinylphenyl)ethane, and hydrogen in propylene polymerization mediated by rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2 and MAO, which gave iPP macromonomer bearing a terminal styryl group (iPP-t-St). Then the iPP-t-St macromonomers of varied molecular mass were engaged in syndiospecific styrene polymerization over a typical mono-titanocene catalyst (CpTiCl3/MAO) under different conditions to produce sPS-g-iPP graft copolymers of varied structure. With an effective purification process, well-defined sPS-g-iPP copolymers were obtained, which were then subjected to differential scanning calorimetry (DSC) and polarized optical micrograph (POM) studies. The graft copolymers were generally found with dual melting and crystallization temperatures, which were ascribable respectively to the sPS backbone and iPP graft. However, it was revealed that the two segments displayed largely different melting and crystallization behaviors than sPS homopolymer and the precursory iPP-t-St macromonomer. Consequently, the graft copolymer exhibited much distinctive crystalline morphologies when compared with their individual components. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.