Preparation of High cis-1,4 Polyisoprene with Narrow Molecular Weight Distribution via Coordinative Chain Transfer Polymerization

High cis-1,4 polyisoprene with narrow molecular weight distribution has been prepared via coordinative chain transfer polymerization (CCTP) using a homogeneous rare earth catalyst composed of neodymium versatate (Nd(vers)(3)), dimethyldichlorosilane (Me(2)SiCl(2)), and diisobutylaluminum hydride (Al(i-Bu)(2)H) which has strong chain transfer affinity is used as both cocatalyst and chain transfer agent (CTA). Differentiating from the typical chain shuttling polymerization where dual-catalysts/CSA system has been used, one catalyst/CTA system is used in this work, and the growing chain swapping between the identical active sites leads to the formation of high cis-1,4 polyisoprene with narrowly distributed molecular weight. Sequential polymerization proves that irreversible chain termination reactions are negligible. Much smaller molecular weight of polymer obtained than that of stoichiometrically calculated illuminates that, differentiating from the typical living polymerization, several polymer chains can be produced by one neodymium atom. The effectiveness of Al(i-Bu)(2)H as a CTA is further testified by much broad molecular weight distribution of polymer when triisobutylaluminum (Al(i-Bu)(3)), a much weaker chain transfer agent, is used as cocatalyst instead of Al(i-Bu)(2)H. Finally, CCTP polymerization mechanism is validated by continuously decreased M(w)/M(n) value of polymer when increasing concentration of Al(i-Bu)(2)H extra added in the Nd(ver)(3)/Me(2)SiCl(2)/Al(i-Bu)(3) catalyst system. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4768-4774, 2010