Borane-functionalized oxide supports: development of active supported metallocene catalysts at low aluminoxane loading

Treatment of hydroxylated silica or alumina with tris(perfluorophenyl)borane (1), bis(perfluorophenyl)borane (2) or bis(perfluorophenyl)boron chloride (3), provides borane-functionalized supports of variable composition, as revealed by in situ monitoring by F-19 NMR spectroscopy and/or elemental analysis. These chemically treated supports can be impregnated with Cp2ZrMe2 to provide supported catalysts for ethylene polymerization. Although some of these supported catalysts are active for ethylene polymerization in the presence of alkylaluminum compounds (e.g., TMA, TIBAL), all of these catalysts are more efficiently activated in the presence of small quantities of methyl aluminoxane, even at very low Al:Zr ratios of 10:1. The polymer properties are quite similar to those produced using the soluble catalyst Cp2ZrMe2/B(C6F5)(3), again in the presence of MAO at low loading. A variety of experiments suggest that minimal leaching of the metallocene complex from the support occurs under the conditions studied; in particular, production of polyethylene with high bulk densities (> 0.2 g/cm(3)) and little reactor fouling, even at elevated temperature in toluene slurry, is observed. (C) 1999 Elsevier Science B.V. All rights reserved.