Abstract: Storage stability of Ziegler-type catalysts for .alpha.-olefin polymerization and having a specific surface greater than 75 m.sup.2 /g is improved by treating the catalysts with a preactivator which is an organic compound of a metal of one of Groups Ia, IIa, IIb and IIIa of the Periodic Table.CROSS-REFERENCE TO RELATED APPLICATIONThe invention described herein is directly related to that described in copending Application Ser. No. 236,407, filed Mar. 21st, 1972. The entire text of that application is incorporated herein by reference.BACKGROUND OF THE INVENTIONZiegler-type microporous catalytic complexes having a specific surface area greater than 75 m.sup.2 /g and useful for the polymerization of .alpha.-olefins are prepared by (a) reducing TiCl.sub.4 by means of an aluminum alkyl; (a') optionally isolating the reduced solid, based on TiCl.sub.

Abstract: Solid catalytic complexes are useful for stereospecific polymerization of .alpha.-olefins to solid crystalline polymers. The complexes are formed by reducing TiCl.sub.4 with an alkylaluminum, treating thus-obtained reduced solid with a complexing agent and contacting the resultant with TiCl.sub.4. They have a specific surface greater than 75 m.sup.2 /g.

Abstract: Process for the polymerization of .alpha.-olefins in the presence of an activator selected from among the organic compounds of metals of groups Ia, IIa, IIb and IIIa of the Periodic Table and a solid catalytic element prepared by(a) reducing TiCl.sub.4 by means of a reducing metal selected from among the metals of groups Ia, IIa, IIb, IIIa of the Periodic Table so as to prepare a double chloride of titanium and the reducing metal(b) treating the double chloride thus prepared by means of a complexant(c) reacting the double chloride thus treated with TiCl.sub.4(d) separating the solid catalytic element thus prepared.