Abstract: A precursor for the formation of catalysts for the (co)polymerization of ?-olefins, comprising titanium, magnesium, at least one metal selected from hafnium and zirconium, aluminum and chlorine, obtained with a process comprising treatment with a siloxane compound. Said solid precursor, used in combination with a suitable co-catalyst in high-temperature (co)polymerization processes of ?-olefins, shows an improved productivity, a high incorporation of co-monomers in the copolymerization of ethylene and an increased thermal stability with respect to the systems so far in use.

Abstract: A precursor for the formation of catalysts for the (co)polymerization of ?-olefins, comprising titanium, magnesium, at least one metal selected from hafnium and zirconium, aluminum and chlorine, obtained with a process comprising treatment with a siloxane compound. Said solid precursor, used in combination with a suitable co-catalyst in high-temperature (co)polymerization processes of ?-olefins, shows an improved productivity, a high incorporation of co-monomers in the copolymerization of ethylene and an increased thermal stability with respect to the systems so far in use.

Abstract: Bimetal catalyst for the (co)polymerization of &agr;-olefins comprising a co-catalyst consisting of a hydride or an organometallic compound of an element of groups 1, 2 or 13 of the periodic table, and a solid component consisting of at least 95% by weight of titanium, magnesium, hafnium, aluminum, chlorine and R—COO carboxylate groups, wherein R is an aliphatic, cycloaliphatic or aromatic hydrocarbon, containing from 1 to 30 carbon atoms, wherein at least 80% of the titanium is in oxidation state +3, and at least 1% of said titanium in oxidation state +3 has a tetrahedral coordination geometry. Said catalyst allows the production of olefinic polymers, particular polyethylene, with a high molecular weight by means of solution polymerization processes at temperatures exceeding 200° C.