CYCLOPENTADIENYL SURFACE AS A SUPPORT FOR ZIRCONIUM POLYETHYLENE CATALYSTS

A novel ethylene polymerization catalyst is prepared by supporting CpZ rCl3 on chemically modified silica. The surface modification of silica was carried out by utilizing the saturated gas-solid reactions of a s ilane coupling agent, Cp(CH2)(3)Si(OCH2CH3)(3), and a partially dehydr oxylated silica. Immobilization of CpZrCl3 onto the cyclopentadienyl s urface formed on the silica was done using liquid-phase reactions. The stepwise-prepared materials were characterized by C-13 and Si-29 soli d 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. T he immobilization of CpZrCl3 on the cyclopentadienyl surface of SiO2 m ore than doubled the polymerization activity of CpZrCl3. However, the direct heterogenization of CpZrCl3 onto an unmodified, partially dehyd roxylated silica produced a catalyst with a very low activity. The eff ect of surface modification reactions and structure of the support on the catalyst performance is presented and discussed.