Study of molecular size in ethylene-propene copolymerization with zirconocene and hafnocene catalysts

Ethylene-propene copolymerization was carried out with Cp₂MCl₂ (Cp = cyclopentadienyl), rac-Et(Ind)₂MCl₂, rac-Me₂Si(Ind)₂MCl₂ (Et = ethylene, Me₂Si = dimethylsilyl, Ind = indenyl, M = Zr or Hf)/methylaluminoxane. In the case of using ansa-hafnocenes, the minimum molecular size (extended chain length) of ethylene-propene copolymer was obtained at about 50 mol-% of propene content in the copolymer. The polymerization activity decreased with increase of propene feed ratio in non-bridged non-specific metallocenes. Higher polymerization activities were observed for the copolymerization compared to ethylene and propene homo-polymerization with ansa-isospecific metallocenes. The factor of molecular size lowering was studied by the chain propagation and chain transfer reaction.