Ethylene/styrene copolymerisation by homogeneous metallocene catalysts: experimental and molecular simulations using rac-ethylenebis(tetrahydroindenyl)MCl 2 [M=Ti,Zr] systems

Abstract

Styrene was copolymerised with ethylene using the catalyst systems [ rac-Et(H 4Ind) 2TiCl 2]/MAO and [ rac-Et(H 4Ind) 2ZrCl 2]/MAO. Keeping other experimental variables under control, we tested different styrene/ethylene ratios in the reactor feed. It was found that the titanium-based catalyst showed very low activity even for ethylene homopolymerisation. In contrast, the zirconium system achieved monomer polymerisation, incorporating small amounts of styrene. When the styrene/ethylene ratio was increased, both catalyst activity and the molecular weight of the resulting copolymers decreased. However, styrene incorporation into the copolymer increased as the styrene/ethylene ratio rose. To gain insight into the copolymerisation mechanisms at play, we undertook a computational study using a high-level hybrid DFT method (B3LYP). Agreement between the experimental and theoretical results was generally good, indicating the usefulness of combined experimental/theoretical studies for clarifying mechanisms of α-olefin copolymerisation using organometallic systems.