FUNCTIONAL SURFACE GROUPS FOR SINGLE-SITE HETEROGENEOUS ALPHA-OLEFIN POLYMERIZATION CATALYSTS

A novel heterogeneous alpha-olefin polymerization catalyst is prepared by the immobilization of CpZrCl3 on a chemically modified silica supp ort. The surface modification of silica was carried out by utilizing t he saturated gas-solid reactions of a silane coupling agent with a hyd rocarbon spacer, Cp(CH2)(3)Si(OCH2CH3)(3), and a partially dehydroxyla ted silica, In gas-solid reactions all reactive surface hydroxyl group s were utilized in bonding the silane coupling agent on silica. The im mobilization of CpZrCl3 on the cyclopentadienyl surface formed on the silica was done using liquid-phase reactions. The prepared materials w ere characterized by FT-IR spectroscopy. The supported catalyst system has a high activity in ethylene polymerization and can be used to pro duce polyethylene with a narrow molecular weight distribution in the p resence of methylaluminoxane. The catalytic activity was doubled when CpZrCl3 was immobilized on the cyclopentadienyl surface of SiO2 compar ed 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 perfo rmance is presented and discussed. (C) 1997 Elsevier Science B.V.