Abstract: A process for the polymerization of ethylene or the copolymerization of ethylene with an alpha-olefin, in suspension or in gas phase, in the presence of a catalyst consisting essentially of a cocatalyst and a catalytic component based on at least Mg, Ti and Cl, with the catalytic component being constituted of at least one derivative of magnesium and one chlorinated derivative of titanium in its form III and/or IV, which was subjected, prior to its use, to a reduction treatment and then to treatment with a chlorinated transition metal compound, with the said catalytic component being characterized in that the magnesium derivative is in the form MgCl.sub.2.MgO.

Abstract: Crystalline MgCl.sub.2 particulates, exhibiting the morphology of substantially regular polyhedra having an even number of from 10 to 18 face surfaces, are well suited as support substrate for olefin polymerization catalysts.

Abstract: A process for the manufacture of MgCl.sub.2.MgO with narrow granulometric distribution by treatment of hydrated MgCl.sub.2 with an alcohol followed by heat treatment after partial elimination of the alcohol, characterized in that the hydrated MgCl.sub.2 is suspended in the alcohol, and that the molar ratio of the alcohol to the hydrated MgCl.sub.2 is lower than the solutility ratio of these two substances at the temperature of the suspension. The resultant MgCl.sub.2.MgO can be employed as a support in catalytic components for the polymerization of olefins.

Abstract: Porous particles of MgCl.sub.2 having the form of essentially regular polyhedrons with six or eight faces in which the paired symmetrically opposite faces are essentially parallel, two of which faces are large and elongated and form the top face and the bottom face of a polyhedron such that on each of them the longest diagonal (D) is larger than the shortest distance (d) separating two opposite sides, which large elongated faces are surrounded essentially perpendicularly by the other essentially rectangular faces that form the sides of the said polyhedron, the length of the smaller side (e) of each of the said essentially rectangular faces being less than the shortest distance (d) separating the two opposite sides of the large elongated faces, catalytic components supported on the particles, catalyst systems utilizing the catalytic products, process for making the particles, and polyolefins obtained utilizing the catalytic systems.

Abstract: A cocatalyst for use in association with a catalytic component comprising a titanium compound and an internal electron donor on a magnesium halide support for the polymerization of propylene alone or propylene with ethylene or a C.sub.4 to C.sub.12 alpha-olefin, said cocatalyst consisting essentially of an organic aluminum compound and an external electron donor consisting essentially of a non-aromatic silane with two Si--O--C bonds and a monoether and/or a silane with a single Si--O--C bond and the resultant catalyst wherein such cocatalyst is combined with a catalytic component known for use in polymerizing propylene.

Abstract: A catalytic component having controlled strucuture for use in combination with a cocatalyst for the polymerization of ethylene, and being the product of the process of subjecting a component consisting essentially of titanium, magnesium, and chlorine to a reduction treatment and after such treatment contacting the component with a transition metal chlorine-containing compound and process of polymerizing ethylene using such catalytic component to produce polymers having a broad molecular weight distribution.

Abstract: A process for the manufacture of a linear polyethylene with narrow molecular-weight distribution comprising polymerizing ethylene alone or a mixture of ethylene and an alpha-olefin in which ethylene represents at least about 70% by weight of the total monomers involved, in a gas-phase polymerization medium in the presence of a catalytic component containing at least one transition metal, magnesium, and a halogen, a co-catalyst comprising an alkylaluminum compound, and a monoether, the monoether having the general formula R'OR", wherein R' and R" are the same or different and each is a C.sub.1 to C.sub.8 linear or branched hydrocarbon radical or being a cyclic monoether with the oxygen forming a ring having 4 to 12 carbon atoms.

Abstract: A catalyst composition for the polymerization of propylene comprising a catalytic solid comprising a titanium halide and a magnesium halide and isoprenyl aluminum associated therewith and the process of polymerizing propylene using such catalyst.

Abstract: A catalyst support consisting essentially of a mixture of silica and magnesium chloride, said support having a porous structure and containing less than 100 micromoles of hydroxyl groups per gram of support; the process of making such support by heating such mixture at a temperature below about 720.degree. C. in the presence of a dehydrating agent, and catalysts consisting essentially of such support and at least one active component.