Catalysts for polymerizing alpha-olefins

Claim 1

Catalysts for polymerizing alpha-olefins CH2 = CHR, in which R is an alkyl radical having 1 to 6 carbon atoms, mixtures thereof, and mixtures thereof with ethylene, including the product of the reaction between at least the following two components: (a) a solid product comprising a Mg dihalide and complexes of said halide with at least a Ti compound and an electron donor compound selected from the group consisting of the esters of the organic and inorganic oxygenated acids, the anhydrides, halides, and amides of said acids, ethers ROR' and ketones RCOR', in which R and R', the same or different from one another, are alkyl, cycloalkyl or aryl radicals having 1 to 18 carbon atoms; in which the Mg/Ti ratio between Mg dihalide and Ti compound ranges from 5 to 100, the amount of Ti compound extractable with TiCl4 at 80°C is lower than 50% and the molar ratio between electron donor compound and Ti compound ranges, after extraction with TiCl4, from 0.2 to 3, and (b) an Al alkyl compound selected from the group consisting of trialkyls, the Al alkyl compounds containing two or more Al atoms bound to one another through an oxygen atom or a nitrogen atom, and compounds AlR3-n(OR')n, in which R is an alkyl radical having 1 to 18 carbon atoms, R' is an aryl radical ortho-hindered in positions 2,6 with substituents capable of giving a steric hindrance higher than that of the group -C2H5, or a naphthyl group containing at least in position 2 a substituent with a steric hindrance higher than that of the group -C2H5, and n is a number comprised in the range from 1 to 2 said Al alkyl compound being present for at least 85% in a non-combined form with an electron donor compound and being employed in amounts corresponding to a molar ratio to the Ti compound of component (a) ranging from 1 to 30; and the ratio between the total moles of electron donor compound and the moles of titanium compound is lower than 5.