SUPPORTED METALLOCENE CATALYSTS AND THEIR USE IN PRODUCING STEREOSPECIFIC POLYMERS

摘要

Supported stereospecific catalysts and processes for the stereotactic propagation of a polymer chain derived from ethylenically unsaturated monomers which contain three or more carbon atoms or which are substituted vinyl compounds, specifically alpha olefins, particularly the polymerization of propylene to produce syndiotactic or isotactic polypropylene. The supported metallocene catalyst comprises a stereospecific metallocene catalyst incorporating a metallocene ligand structure having two sterically dissimilar cyclopentadienyl ring structures coordinated with the central transition metal atom, and a co-catalyst component comprising at least one of an alkyl alumoxane and an alkylaluminum compound At least one of the cyclopentadienyl ring structures is a substituted cyclopentadienyl group which provides an orientation with respect to said transition metal atom which is sterically different from the orientation of the other cyclopentadienyl group, and both of the cyclopentadienyl groups are in a stereorigid relationship with one another by virtue of bridge or substituent groups, which prevent rotation of said ring structures. Both the metallocene catalyst and the co-catalyst are supported on a particulate silica support comprising silica particles having an average particle size of 5-40 microns and an average effective pore size of 50-200 angstroms. The silica support further has a differential pore size distribution of a pore volume of at least 0.01 cm²/g. within a range having a maximum pore width of no more than 300 angstroms. The metallocene has a retention factor on this support of at least 90 wt. % after aging in tri-isobutylaluminum at a temperature of 25 °C for a period of 12 hours.