Ziegler-Natta catalyst for prodn. of atactic (co)polyolefin - produced from titanium tetra:chloride, organo-magnesium cpd. and organo-aluminium cpd

Ziegler-Natta catalyst for the polymerisation of 3-8C 1-olefins and their copolymerisation, opt. with C2H4, to atactic polyolefins, opt. in the presence of H2, consists of TiCl4 and organo-Mg cpd. as catalyst and organo-Al cpd. as cocatalyst. Improvement comprises (a) reducing TiCl4 with an organo-Mg cpd. dissolved or suspended in an inert liq. hydrocarbon and opt. sepn. of the insoluble reaction prod. (b) impregnating the insoluble solid with TiCl4; (c) reacting with an organo-Al cpd. in an inert liq. hydrocarbon and sepg. the insoluble reaction prod. from the mixt.; and (d) activating the reaction prod. with an organo-Al cpd. Before activation in stage (d), the catalyst pref. is treated first with a Lewis base and then with a Lewis acid. Very high activity and high atacticity are obtd. Atactic polyolefins are useful e.g. in various coatings.