Abstract: A process for the manufacture of a modified titanium component for catalysts of the Ziegler/Natta type by milling a mixture of a titanium compound of the formula TiCl.sub.3 .13AlCl.sub.3 and an organic electron donor containing phosphorus and/or nitrogen atoms. The characterizing feature is that the mixture is first milled wet in a liquid inert hydrocarbon medium under specific conditions, then separated from the hydrocarbon medium and finally milled dry under specific conditions. Such modified titanium components give catalysts which provide particularly well reproducible results in the polymerization of .alpha.-olefins.

Abstract: A process for the manufacture of poly(.alpha.-olefins) by polymerization of .alpha.-olefins using a catalyst system comprising (1) a titanium-containing component of (1.1) a substance of the formula TiCl.sub.3 . 1/3 AlCl.sub.3 and (1.2) an organic electron donor containing phosphorus atoms and/or nitrogen atoms, ground together with said substance (1.1), and (2) an aluminum-containing component of a substance of formula Al(C.sub.n H.sub.2 ..sub.n.sub.+1).sub.3 or Al(C.sub.n H.sub.2..sub.n.sub.+1).sub.2 Cl, where n is an integer of from 2 to 6. The characteristic feature is that the catalyst system used is one in which the component (1.1) has been ground with component (1.2) without the use of auxiliaries or additives in a vibratory ball mill using specific steel balls and a specific grinding acceleration over a specific period of time at a temperature which is just below that at which the particles in the ground material begin to agglomerate.