Cyclopentadienyl surface as a support for zirconium polyethylene catalysts

A novel ethylene polymerization catalyst is prepared by supporting CpZrCl3 on chemically modified silica. The surface modification of silica was carried out by utilizing the saturated gas-solid reactions of a silane coupling agent, Cp(CH2)(3)Si(OCH2CH3)(3), and a partially dehydroxylated silica. Immobilization of CpZrCl3 onto the cyclopentadienyl surface formed on the silica was done using liquid-phase reactions. The stepwise-prepared materials were characterized by C-13 and Si-29 solid state NMR and FT-IR spectroscopy. This supported catalyst system has a high activity and can be used to produce polyethylene with a narrow molecular weight distribution in the presence of methylaluminoxane. The immobilization of CpZrCl3 on the cyclopentadienyl surface of SiO2 more than doubled the polymerization activity of CpZrCl3. However, the direct heterogenization of CpZrCl3 onto an unmodified, partially dehydroxylated silica produced a catalyst with a very low activity. The effect of surface modification reactions and structure of the support on the catalyst performance is presented and discussed.