Manufacture of particulate homopolymers or copolymers of ethylene

A process for the manufacture of particulate ethylene homopolymers (HP) or ethylene copolymers (CP) containing up to 20% by weight of polymerized units of C.sub.3-8 .alpha.-monoalkene, which polymers have a particle size of from 0.1 to 6 mm and are obtained by polymerization of ethylene or ethylene/C.sub.3-8 .alpha.-monoalkene mixtures in a dry, agitated bed (B) of particulate homopolymer (HP) or copolymer (CP) at temperatures of from 30.degree. to 120.degree.C and pressures of from 1 .times. 10.sup.5 to 2 .times. 10.sup.7 N/m.sup.2 (Pascal) by means of a Ziegler/Natta catalyst system consisting of (1) a titanium-containing component and (2) an aluminum (C.sub.1-8 trialkyl) or aluminum (C.sub.1-8 dialkyl) chloride, provided that (I) the components (1) and (2) of the catalyst system are separately fed to the bed (B) and (II) the atomic ratio of titanium in component (1) to aluminum in component (2) is from 1:0.1 to 1:1,000, wherein the titanium-containing component (1) of the catalyst system is a particulate reaction product (U) having a particle diameter of from 0.1 to 2,000 .mu.m and obtained from

• 1.1. a substance of the formula TiCl.sub.3 . (AlCl.sub.3).sub.n, where n is a number equal to from 0 to 0.34, and
• 1.2. a reaction product (R) of phosgene and a substance (S) which has been obtained from a substance of the formula Mg.sub.6 . Al.sub.2 . (OH).sub.16 . CO.sub.3 . (H.sub.2 O).sub.4 by calcination (heating) at a temperature of from 100.degree. to 600.degree.C for from 1 to 100 hours,
• provided that (III) the reaction product (R) has been obtained by allowing phosgene to act on the substance (S) at a temperature of from 80.degree. to 350.degree.C until the reaction product (R) has a chlorine content of from about 50 to 65% by weight and (IV) the reaction product (U) has been obtained by milling its components (1.1) and (1.2) together in a vibratory ball mill in a ratio of from 1:2 to 1:200 by weight over a period of time ranging from 5 to 100 hours, the milling acceleration being from 4 to 6 m/s.sup.2.