High efficiency catalyst containing titanium, zirconium and zinc for polymerizing olefins

Compositions, exhibiting high catalytic activity in the polymerization of a-olefins, are prepared by reacting trivalent or tetravalent titanium compounds such as titanium tetraalkoxides, zirconium compounds such as tri-n-butoxy zirconium chloride, an organomagnesium component such as di-n-hexyl magnesium, a halogen source such as ethyl aluminum dichloride, a divalent zinc compound such as diethyl zinc and an organoaluminum compound if the halide source or magnesium component does not contain sufficient quantities of aluminum. Polymerization processes employing this catalyst composition do not require conventional catalyst removal steps in order to provide polymers having suitable color and other physical characteristics and these catalysts produce polymers having broader molecular weight distributions and lower melt indices than do corresponding catalysts without both the divalent zinc and zirconium compounds