Effects of Al/Zr ratio on ethylene-propylene copolymerization with supported-zirconocene catalysts

Effects of heterogenization parameters on compositional and catalytic prope rties of Et(Ind)(2)ZrCl2 supported on silica modified with MAO were evaluat ed using data on metal loading, catalyst activity in ethylene-propylene cop olymerization, and polymer properties. The supported catalysts were prepare d according to a 2(3) factorial design for multivariate analysis. The param eters studied were: MAO concentration in impregnation, Et(Ind)(2)ZrCl2 conc entration in grafting, and immobilization temperature for both metallocene and organoaluminum. The grafting solution was monitored by UV-VIS spectrosc opy, while the resulting catalyst systems were characterized by inductively -coupled plasma-optical emission spectroscopy (ICP-OES), diffuse reflectanc e infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). At high statistical significance, both MAO and Et(Ind) (2)ZrCl2 concentrations during preparation affected the determination of th e find Al/Zr ratio on silica, The catalyst systems were tested in ethylene- propylene copolymerizations using external MAO as cocatalyst. Relationships were observed between (i) catalyst activity and the binding energy of Zr 3 d(5/2) electrons and (ii) Al/Zr ratio on silica and the average ethylene in corporation. The polymer samples presented narrow molecular weight distribu tion, but according to differential scanning calorimetry (DSC), and cross-f ractionation chromatography (CFC) data, catalyst systems with given Al/Zr r atios might yield different crystallites, suggesting a plural distribution of chemical composition. (C) 2001 Elsevier Science B.V. All rights reserved .