Regio‐chemistry control in propylene/isoprene copolymerization by metallocene catalysts

Abstract

AbstractRegio‐chemistry control in copolymerization of propylene with isoprene is pursued with C2‐symmetric ansa‐metallocene catalysts in order to efficiently synthesize isotactic polypropylene bearing pendant vinylidene functionality (iPP‐g‐VD) using isoprene as a convenient asymmetric diene feedstock. Two paths are taken by employing two well‐known but structurally different metallocenes that exhibit discrepant regio‐chemistry for α‐olefin insertion, namely rac‐Me2Si(2‐Me‐4‐Ph‐Ind)2ZrCl2 (1) and rac‐CH2(3‐t‐Bu‐Ind)2ZrCl2 (2), both of which tend to an improvement of isoprene 4,3‐ (primary) insertion specificity whilst depressing the regio‐reversed 3,4‐ (secondary) insertion. In the case of using 1–methylaluminoxane (MAO), the strategy is to use increased dosage of H2 to effectively integrate isoprene 3,4‐insertion into iPP main chain without developing π‐allyl–metal deadlock. In the case of using 2–MAO, however, the sterically highly hindered ligand structure only accommodates primary isoprene 4,3‐insertion. Synthesis of iPP‐g‐VD becomes much more controllable, with up to 1.91 mol% of side‐chain vinylidene groups having been realized on iPP, at fairly good catalyst activities and little or no sacrifice of polymer molecular weight. iPP‐g‐VD is revealed to be fully eligible as an intermediate for accessing polar‐functionalized polypropylene, with both hydroboration and subsequent hydroxylated functionalization and poly(methyl methacrylate) grafting proceeding with high yields. © 2015 Society of Chemical Industry