Abstract: Solid catalyst components for use in the polymerization of olefins and having improved activity and selectivity are prepared by:(a) halogenating a magnesium compound containing at least one aryloxy, alkyl carbonate or alkyloxy group with a first halide of tetravalent titanium and a first electron donor;(b.sub.1) contacting the resulting halogenated product with a second halide of tetravalent titanium; and(c) washing a resulting treated halogenated product with an inert hydrocarbon liquid, wherein a second electron donor is used in step (a) or step (b.sub.1) and in that the product of step (b.sub.1) is contacted in a step b.sub.2 with a third halide of tetravalent titanium at a temperature of 40.degree. to 140.degree. C. and thereafter the treated product is washed in step (c).

Abstract: Olefin polymerization catalyst components having improved activity and morphological properties are disclosed and claimed. In particular, the components are prepared by reacting a carbonized magnesium alkoxide or aryloxide component with a halogenated tetravalent titanium component, a halohydrocarbon component and an electron donor.

Abstract: Olefin polymerization catalyst components having improved activity and morphological properties are disclosed and claimed. In particular, the components are prepared by reacting a carbonized magnesium alkoxide or aryloxide component with a halogenated tetravalent titanium component, a halohydrocarbon component and an electron donor.