New supported catalysts on the basis of cyclopentadienylindenylzirconium dichloride (CpIndZrCl,) anchored on silica with a trisiloxane spacer (ZATS) and a pentamethylene spacer (ZAPM) were prepared and used for ethylene polymerization with modified methylaluminoxane (MAO) as cocatalyst. ZATS and ZAPM produce polyethylene with lower molecular weight but show higher activity than silica-supported CpIndZrCl, which was prepared by reacting zirconocene directly with silica, i. e., the activity of silica-supported CpIndZrCl, is enhanced by introducing a spacer between silica surface and metallocene species.
Two kinds of the trisiloxane-bridged dinuclear titanium metallocene-type complexes were synthesized. They are monocyclopentadienyl and biscyclopentadienyl dinuclear titanocenes with trisiloxane bridges. The above complexes with modified methylaluminoxane (MMAO) cocatalyst initiate the polymerizations of ethylene and styrene to produce high-density polyethylene and syndiotactic poIystyrene. In addition, a copolymer of ethylene and styrene was obtained.
In the polymerization of ethene cocatalyzed with modified methylaluminoxane, the catalyst activities of the siloxane-bridged dinuclear zirconocenes, tetramethyldisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) (3) and hexamethyltrisiloxanediylbis(cyclopentadienylindeny1zirconium dichloride) (4) were lower than that obtained with the siloxane-bridged mononuclear zirconocene, tetramethyldisiloxanediyldicyclopenl_adienyldimethylzirconium (1). On the other hand, weight-average molecular weight M, and ratio of weight-to number-average molecular weights Mw/H,, of polyethene (PE) obtained with 3 or 4 were higher than those of PE obtained with 1. For a binary mixture of 1/3 or 1/4, it was found that the obtained PE exhibits a bimodal molecular weight distribution for an appropriate composition of the mixed zirconocenes. mw/@,, of PE could be adjusted by changing the relative concentrations of the two zirconocenes. 0 1996,
The disiloxane-bridged zirconocene complexes, tetramethyldisiloxanediylbis(cyclopentadieny1)zirconium dichloride and tetramethyldisiloxanediylbis(cyc1opentadienyl)dimethylzirconium initiate the homopolymerization of ethene as well as the copolymerization of ethene and a-olefin with a modified methylaluminoxane as cocatalyst. The catalyst systems give resonable activity but the molecular weight of polyethene decreases drastically with increasing polymerization temperature.
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