Heterogeneous metallocene catalysts for ethylene polymerization

The catalyst precursor 9-fluorenylidene-1 -cyclopentadienylidene-2-hex-5-en ylidene zirconium dichloride proved to be highly active in the heterogeneou sly catalyzed polymerization of ethylene using silica gel/partially hydroly zed trimethylaluminum (PHT) as cocatalyst. The substitution of position 4 o f the fluorenylidene fragment and position 3 of the cyclopentadienylidene r ing improves the catalyst activity. The introduction of a phenyl group into the bridge increases the catalyst activity and the molecular weight of the polymer. The prepolymerization of this catalyst system leads to a major ch ange in catalyst and polymer properties. A significant increase in catalyst activity and a lower molecular weight of the produced polyethylene is obse rved. The presence of hydrogen during prepolymerization or polymerization o f ethylene produces a broader molecular weight distribution indicating a hi gher number of different active centers. (C) 2001 Elsevier Science B.V. All rights reserved.