Polymerization of olefins in the presence of Ziegler-Natta catalysts containing VOCl3
The reasons for the low activity of vanadium-based Ziegler-Natta catalysts in the polymerization of ethylene have been discussed. A very easy and rapid reduction of vanadium(IV) as well as vanadium(III) to the inactive vanadium(II) form by an organoaluminum cocatalyst in the VOCl3/Et2AlCl system was confirmed. Deactivation of active sites was found to increase as the catalyst aging time and polymerization temperature are increased. Deposition of the relatively unstable vanadium catalyst on a MgCl2(THF)2 support resulted in stabilized vanadium active sites because of suppressed reduction to the inactive state of lower valency. Optimum conditions were established for of the synthesis of a high-activity and high- -stability supported vanadium catalyst. This catalyst system produced PE-UHMW. The specific role of MgCl2(THF)2 as a carrier of Ziegler—Natta type catalysts was discussed in terms of catalytic properties of various titanium and vanadium systems.
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