Ethylene polymerization with methylaluminoxane/(nBuCp)2ZrCl2 catalyst supported on silica and silica‐alumina at different AlMAO/Zr molar ratios

Methylaluminoxane (MAO)/(nBuCp)₂ZrCl₂ metallocene catalytic system was supported on silica and silica‐alumina. The Zr loading was varied between 0.2–0.4 wt %, and the MAO amount was calculated to get (Al_MAO/Zr) molar ratios between 100 and 200, suitable for the industrial ethylene polymerization of supported metallocene catalysts. Catalytic activity was statistically analyzed through the response surface method. Within the ranges studied, it was found that Zr loading had a negative effect on polymerization activity, which increases with the (Al_MAO/Zr) molar ratio. Catalysts supported on silica‐alumina are more active than those supported on silica, needing less MAO to reach similar productivity, which constitutes an important advantage from an economical and environmental point of view. Supported catalysts were characterized by ICP‐AES, SEM‐energy‐dispersive X‐ray spectrometer, and UV‐Vis spectroscopy, whereas polyethylenes were characterized by GPC and DSC. Molecular weight and crystallinity are not influenced by Zr loading or (Al_MAO/Zr) ratio, in the range studied. In general, silica‐supported MAO/(nBuCp)₂ZrCl₂ catalysts give polyethylenes with higher molecular weight and polydispersity but lower crystallinity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011