ELECTROCHEMICAL SYNTHESIS OF TITANIUM-BASED ZIEGLER-NATTA CATALYSTS AND THEIR POTENTIAL APPLICATION IN ETHYLENE HOMOPOLYMERIZATION AND COPOLYMERIZATION

Highly active Ziegler-Natta catalysts have been synthesized using an e lectrochemical process in their preparation, with the aim of producing selectively titanium(III) species from TiCl4. The use of an undivided cell, an aluminium anode and a halogenated solvent (dichloromethane o r 1,2-dichloroethane), has allowed the production in situ of chloroalk ylaluminium species, by cathodic reduction of TiCl4, thus giving rise to a new Ziegler-Natta catalytic combination. The possibility of scale up for this electrochemical synthesis has been clearly shown. The Ti/ Al system was modified so as to enhance its activity, first by adding a soluble dialkylmagnesium compound and then a soluble vanadium compou nd such as VOCl3. This Ti/Al/Mg/V highly active system was used under different conditions: in a hydrocarbon medium at low (80 degrees C) an d high (200 degrees C) temperature and also under supercritical condit ions in a continuous high-pressure autoclave reactor, to produce homo- or copolymers of ethylene with alpha-olefins. Compared to similar het erogeneous catalysts obtained by comilling, the observed activities ar e shown to be very much improved, especially under high pressure and h igh temperature conditions. This may be related to the very narrow gra nular distribution centered at 2,5-3 mu m, compared to a much broader distribution (centered at 6 mu m) obtained with the comilled catalyst.