POLYMERIZATION OF ETHYLENE BY ZIRCONOCENE-B(C6F5)(3) CATALYSTS WITH ALUMINUM COMPOUNDS

Ethylene polymerization by zirconocene-B(C6F5)(3) catalysts with vario us aluminum compounds has been investigated. It is found that the cata lytic activity depended on zirconocenes used, and especially on the ty pe of aluminum compounds. For Et(H(4)Ind)(2)ZrCl2 (H(4)Ind : tetrahydr oindenyl), the activity decreases in the following order: Me3Al > i-Bu 3Al > Et3Al much greater than Et2AlCl. While for Cp2ZrCl2(Cp : cyclope ntadienyl), it varies as follows: i-Bu3Al > Me3Al much greater than Et 3Al. Furthermore, the activity is significantly affected by the additi on mode of the catalytic components, which may imply that the formatio n of active centers is associated with an existing concentration of ca talytic components. Results of thermal behavior of polyethylene (PE) s tudied by differential scanning calorimetry(DSC) show that crystallini ty of the polymer prepared with Et3Al is higher than that with Me3Al o r i-Bu3Al. It is also found that the number-average molecular weight ( (M) over bar) of the polymers prepared with Me3Al or i-Bu3Al is much h igher than that with Et3Al. H-1-NMR studies substantiate that i-Bu3Al is a more efficient alkylation agent of Cp2ZrCl2 in comparison with Me 3Al. (C) 1997 John Wiley & Sons, Inc.