Abstract: Catalysts component of the (co)polymerization of alpha-olefins CH.sub.2 .dbd.CHR, wherein R is hydrogen or an alkyl radical having from 1 to 8 carbon atoms, comprising a product of the composition:VCL.sub.y.z(b)wherein (b) represents an organic compound selected from alkyl, aryl and acyl halides, y is a number higher than 2 and lower than 4, and preferably comprised between 2.5 and 3.5 and z is a number higher than zero and lower than or equal to 2, and preferably between 0.002 and 1. Components can be obtained as products of the reaction, carried out at temperatures higher than 10.degree. C., between VCl.sub.4 and the compound (b). Particularly preferred among compounds (b) are benzoyl chloride, p-methoxybenzoyl chloride and p-chloro benzoyl chloride. From the components of the invention, either supported or not, catalysts having high activity particularly useful for the production of ethylene polymers showing broad molecular weight distribution can be prepared.

Abstract: Process for preparing elastomeric copolymers of ethylene with .alpha.-olefins CH.sub.2 .dbd.CHR, optionally containing minor proportions of a diene, characterized by the use during the polymerization of a catalyst comprising the reaction product of:(I) a solid component comprising VCl.sub.3 supported on a magnesium dihalide in spherical or spheroidal shape, in active form;(II) an alkyaluminum compound;(III) optionally a halohydrocarbon.VCl.sub.3 is precipitated on said magnesium dihalide by heating VCl.sub.4 solutions in inert hydrocarbon solvents.

Abstract: Solid catalyst component for the polymerization of ethylene including the product of the reaction between:1) the product obtained by reacting:1A) a halide, halogen alcoholate or alcoholate of titanium, vanadium or zirconium;1B) a small quantity of water, and optionally1C) a compound or composition capable of substituting, in compound 1A, one or more alkoxy groups with a halogen atom; and2) a complex having general formula:MgX.sub.2 .multidot.nAlRX.sub.2 .multidot.pAlX.sub.3where X is chlorine or bromine; R is a hydrocarbon radical containing from 1 to 20 carbon atoms; n is a number from 1 to 4; p is a number from 0 to 1, and n+p from 1 to 4;the catalyst component being in the form or particles having a diameter lower than or equal to 20 micrometers, and an average diameter lower than or equal to 10 micrometers.