Preparation, characterization, and activity of silica supported metallocene catalysts

Silica supported metallocene catalysts were prepared for ethylene polymerization by immobilizing bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂) onto both calcined silica, and silica treated with γ-aminopropyltrimethoxysilane or γ-mercaptopropyltrimethoxy- silane. Bis(cyclopentadienyl)zirconium chloride hydride (Cp₂ZrClH) was also immobilized onto both calcined silica and vinyltrimethoxysilane treated silica. The catalysts were characterized by using direct current plasma atomic emission spectroscopy (DCP-AES), diffuse reflectance infrared spectroscopy (DRIFT), and X-ray photoelecton spectroscopy (XPS). It was found that both Cp₂ZrCl₂ and Cp₂ZrClH were adsorbed on both calcined silica and silane treated silica, respectively. When γ-aminopropyltrimethoxysilane (APTMS) was used as the spacer molecule, some of the amine became protonated upon adsorption of Cp₂ZrCl ₂. Initial catalytic tests showed that all of the complexes were catalytically active (methylaluminoxane as a cocatalyst), with the Cp ₂ZrClH supported complexes giving the highest activities, but still lower than the homogeneous catalyst, Cp₂ZrCl₂. The supported complexes produced polymer with higher molecular weight than the homogeneous catalyst. These observations, together with presented spectral evidence, support the view that the catalyst remained adsorbed in the presence of MAO.