| 摘要 |
A process for the preparation of (i) polyethylene or (ii) polypropylene, which is essentially isotactic or a mixture of atactic and isotactic polypropylenes comprising contacting ethylene or propylene per se, or in admixture with one or more alpha-olefins, under polymerization conditions, with a catalyst system comprising:(a) a precatalyst comprising a mixture of racemic and meso stereoisomers of a metallocene catalyst containing two cycloalkadienyl ligands joined by a bridging linkage, said ligands complexed to a metal atom; and(b) (1) to obtain polyethylene catalyzed by the rac epimer only, a cocatalyst selected from the group consisting of tris(perfluorophenyl)borane and isobutyl alumoxane; (2) to obtain polyethylene catalyzed by both the rac and the meso epimers, a cocatalyst selected from the group consisting of dimethylanilinium tetrakis(perfluorophenyl)borate and triphenylmethyl tetrakis(perfluorophenyl)borate; (3) to obtain polypropylene, which is essentially isotactic, a cocatalyst selected from the group consisting of tris(perfluorophenyl)borane and isobutyl alumoxane; (4) to obtain polypropylene, which is a mixture of atactic and isotactic polypropylenes in a weight ratio of atactic to isotactic polypropylenes of about 0.01:1 to about 1:1, a cocatalyst selected from the group consisting of dimethylanilinium tetrakis(perfluorophenyl)borate and triphenylmethyl tetrakis(perfluorophenyl)borate.
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