Magnesium chloride in zirconocene catalysts used for polymerization of ethylene

The activity and stability of zirconocene catalysts immobilized on magnesium chloride modified with an organoaluminum compound AlR3 (R = Me or Et) were studied in the polymerization of ethylene (Tables 1, 2). An original method was used to introduce a Lewis internal base into the magnesium support. Trace amounts of water present in magnesium chloride were assumed to react with the organoaluminum compound to produce on the surface of the chloride an alkylaluminoxane [R2AlOAlR2] with the basic centers functioning as a Lewis internal base. The resulting support was used to immobilize a zirconocene compound which, when activated with MAO, became a very active complex catalyzing the polymerization of ethylene at a constant rate (284 kg PE/g Zr . h). Catalytically active centers were found to occur in the solvent solution only (and not on the solid support surface) at a concentration found to be nearly equal to that of water in the magnesium chloride. The ethylene polymerization kinetics studied with two catalysts systems prepared and the physical and mechanical property data measured for the resulting PE (Table 2) allowed to infer the highly stable zirconocene homogeneous catalyst system to have magnesium atom incorporated into the following structure [ClMgOAlR2/Cp2ZrCl2]. The modifier AlR3 was found to affect the physical and mechanical properties of the resulting PE (Table 2).