Abstract: A catalyst system of such high efficiency that the purification of the polymer can be dispensed with is obtained by first reacting a magnesium halide with an electron donor and/or a cyclopolyene, bringing the product obtained into contact with a TiCl.sub.3 -containing compound and using a stereoregulator. The system has a high stereospecificity whereby the proportion of atactic polymer is kept low. No excess amount of transition metal halides is required and the polymer obtained has uniform coarse particles and a very low halogen content. spThis is a continuation, of application Ser. No. 54,922 filed July 5, 1979, now abandoned.

Abstract: A polypropylene having a strongly reduced melting temperature and improved optical properties is obtained by copolymerization of propylene with small quantities of ethylene and butene-(1).

Abstract: A catalyst of high activity and stereospecificity in .alpha.-olefin polymerization is obtained when titanium trichloride, prepared from titanium tetrachloride by reduction with an aluminum alkyl halide, is thermally treated, first with an ether in the presence of a cyclopolyene and the solid reaction product is then treated with an aluminum alkyl halide in the presence of a small amount of a cyclopolyene and/or an olefin. With the catalyst obtained high space-time yields of .alpha.-olefin polymers and copolymers can be produced.

Abstract: A catalyst of high activity and stereospecificity in .alpha.-olefin polymerization is obtained when titanium trichloride, prepared by reduction with aluminum alkyl halides, is treated first with an ether and then, without separation of the ether, with an aluminum alkyl halide in the presence of a small amount of a cyclopolyene and/or an olefin.

Abstract: A catalyst of high activity and stereospecificity in .alpha.-olefin polymerization is obtained by subjecting titanium trichloride, obtained by reduction of titanium tetrachloride with aluminum alkyl halides, to two thermal treatments, the second thermal treatment being carried out in the presence of a dialkyl ether.

Abstract: A catalyst of high activity and stereospecificity in .alpha.-olefin polymerization is obtained by subjecting titanium trichloride, prepared from titanium tetrachloride by reduction with aluminum alkyl halides, to two thermal treatments, the second one being carried out in the presence of an dialkyl ether and a cyclopolyene, and/or after-treating the solid reaction product with an aluminum alkyl halide, optionally in the presence of a small amount of a cyclopolyene and/or an olefin.

Abstract: A polypropylene molding composition having an excellent impact strength at a temperature down to -60.degree. C and simultaneously a good hardness contains from 70 to 90% by weight of a polypropylene, 2 to 10% by weight of an ethylene propylene copolymer and 8 to 25% by weight of a polyethylene and is distinguished by a melt index MFI 230/5 lower than that of the polypropylene contained therein and simultaneously higher by the coefficient 1.3 to 7.0 than that of a polypropylene prepared in the presence of the same catalyst as the molding composition and having the same RSV.