Abstract: An improved process for polymerizing .alpha.-alkenes and using Ziegler-type catalyst compositions is described.The Ziegler-type catalyst composition comprises a component consisting of an organoaluminum compound, an organomagnesium compound and a titanium compound or their reaction products on an inorganic porous solid particulate carrier material, wherein the aluminum/magnesium/titanium components are distributed and absorbed onto the inorganic carrier material, in separate steps, with removal of solvent or diluent therein between whereby the final catalyst/carrier composition when used in the polymerization process produces solid particulate polymer products with narrow particle size distributions.

Abstract: A process for polymerizing .alpha.-olefins in the liquid phase is disclosed, wherein the olefins are polymerized in the presence of a catalyst prepared by first reacting as aluminum-halogen compound with an organomagnesium compound and thereafter reacting the resulting reaction mixture with a transition metal compound and then activating the resulting catalyst system with an organo-aluminum compound. The homopolymers and copolymers of .alpha.-olefins produced by this process find use in the normal applications of such polymers.