Functional surface groups for single-site heterogeneous α-olefin polymerization catalysts

A novel heterogeneous α-olefin polymerization catalyst is prepared by the immobilization of CpZrCl3 on a chemically modified silica support. The surface modification of silica was carried out by utilizing the saturated gas-solid reactions of a silane coupling agent with a hydrocarbon spacer, Cp(CH2)3Si(OCH2CH3)3, and a partially dehydroxylated silica. In gas-solid reactions all reactive surface hydroxyl groups were utilized in bonding the silane coupling agent on silica. The immobilization of CpZrCl3 on the cyclopentadienyl surface formed on the silica was done using liquid-phase reactions. The prepared materials were characterized by FT-IR spectroscopy. The supported catalyst system has a high activity in ethylene polymerization and can be used to produce polyethylene with a narrow molecular weight distribution in the presence of methylaluminoxane. The catalytic activity was doubled when CpZrCl3 was immobilized on the cyclopentadienyl surface of SiO2 compared with the activity of CpZrCl3 in homogeneous catalysis. However, the direct heterogenization of CpZrCl3 onto unmodified silica produced a catalyst with a very low activity. The effect of surface modification reactions and the surface structure of a support on the catalyst performance is presented and discussed.