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

Regio‐chemistry control in copolymerization of propylene with isoprene is pursued with C 2 ‐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 ‐ Me 2 Si (2‐Me‐4‐Ph‐Ind) 2 ZrCl 2 ( 1 ) and rac ‐ CH 2 (3‐ t ‐Bu‐Ind) 2 ZrCl 2 ( 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 H 2 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