Abstract: Polymer compositions comprising .alpha.-olefin polymers and a minor proportion of synthetic basic zeolite are stabilized against the harmful effects of corrosion of metal surfaces when processed through mechanical equipment such as molds and extruders where the composition normally contacts metal surfaces.

Abstract: A high activity olefin polymerization catalyst catalyzes the production of polymeric lower .alpha.-olefin having good properties. The catalyst is produced from an organoaluminum cocatalyst, a selectivity control agent and a novel olefin polymerization procatalyst which is prepared by contacting a tetravalent titanium halide, an optional inert diluent, an electron donor and a novel solid procatalyst precursor obtained by contacting (a) a carbonated magnesium alkoxide of the general formula ##STR1## wherein R is a hydrocarbyl group having up to 12 carbon atoms and x is a number from 0.1 to about 2; and (b) at least one halogenating compound which is a non-transition metal halogenated compound or non-metallic halogenated compound. A process for polymerizing one or more .alpha.-olefins utilizing the novel high activity polymerization catalyst.