Ethylene polymerization catalyzed by metallocene/methylaluminoxane systems: quantum-mechanical study on the role of olefin separated ion pairs (OSIP) in the polymerization mechanism

Abstract

DFT (density-functional theory) calculations were performed to investigate the thermodynamics of formation of Olefin Separated Ion Pairs (OSIP) Cp2MtCH3+/C2H4/Cl2Al[O(AlMe3)AlHMe] (Cp = η5-C5H5, Mt = Ti, Zr, Me = CH3) from ethylene and Cp2MtMe · Cl2Al[O(AlMe3)AlHMe]2, a model of adduct produced by metallocence/methylaluminoxane (MAO) systems for olefin polymerization. The results account for the high cocatalytic activity of MAO and show that titanium complexes are potentially more active than zirconium homologues, as confirmed by low temperature polymerization tests.