IRS study of ethylene polymerization catalyst SiO2/methylaluminoxane/zirconocene

IR spectroscopy has been used to study the interaction of silica with two methylaluminoxane (MAO) samples differed by trimethylaluminium (TMA) content and with TMA. MAO and TMA have been shown to react with silica in a different way. Whereas TMA interacts with terminal hydroxyl groups of silica via the protolysis reaction, MAO mainly adsorbs on the surface hydroxyl groups of silica without noticeable protolytical reaction with them. When silica is treated with commercial grade MAO with significant TMA content, the silica surface hydroxyl groups mainly interacts with TMA and MAO adsorbs on the surface of SiO(2)/TMA sample. Lewis acidic sites (LAS) of silica, modified with TMA and MAO samples differed by TMA content, have been investigated by IR spectroscopy (CO adsorption as probe molecule at 77 K). Two types of LAS were found on the surface of silica modified with MAO and TMA: LAS of moderate strength (v(CO) = 2204-2212 cm(-1)) and weak LAS (v(CO) = 2194 cm(-1)). The concentration of these acidic sites was estimated. By anchoring of Cp(2)ZrCl(2) on silica, modified with TMA and MAO, the corresponding catalysts SiO(2)/TMA/Cp(2)ZrCl(2) and SiO(2)/MAO/Cp(2)ZrCl(2) were prepared and tested at ethylene polymerization. Some correlations between the amount and strength of surface LAS of supports, catalysts composition and their activity are discussed. It is proposed that the surface active species are formed at zirconocene interaction with the most strong LAS. (C) 1999 Elsevier Science B.V. All rights reserved.