Abstract: An active catalyst in the polymerization of alpha-olefins is obtained by:(i) bringing a dialkyl magnesium, or an alkyl magnesium halide into contact with a silicon or tin halide, in solution in an inert organic solvent, until a granular solid precipitates off;(ii) suspending said solid precipitate in an inert organic solvent and bringing it into contact with a compound which can be defined by the formula: ##STR1## wherein M represents a metal from Group IVB of the Periodic Table of Elements, and each R and C.sub.p has the meaning as reported in the disclosure, in order to form a granular solid catalyst; and(iii) recovering said solid catalyst from the resulting suspension.

Abstract: A supported catalyst for the (co)polymerization of alpha-olefins is obtained by putting the following products in contact with each other:(A) a metallocene derivative of a metal selected from the group consisting of transition metals and lanthanides, which is in itself capable of promoting the polymerization of alpha-olefins in the presence of or also without suitable activators;(B) an active support containing magnesium, halogen, titanium and smaller quantities of tin;(C) an organometal derivative of aluminium of which at least 50% of the aluminium atoms are bound to at least one alkyl carbon atom.Components (A) and (B) are preferably interacted first to obtain a supported metallocene derivative, which is then put in contact with (C) to obtain the desired catalyst. Alternatively, (B) and (C) are interacted and subsequently put in contact with (A).

Abstract: During the reaction of grafting of styrene and acrylonitrile to polybutadiene, the conversion of the graft monomers is increased from the values of 92.div.94% usually obtained, to values very close to 98%, by carrying out a redox-type reaction additional to that provided by the process, in the presence of an additional aliquot of acrylonitrile and of catalytic system.

Abstract: Polymerization catalysts, particularly catalysts for the polymerization of olefins, are disclosed. The catalysts are prepared by mixing hydrides of organometallic compounds of metals belonging to Groups I to III of the Mendelyeev Periodic Table with products obtained by contacting (1) titanium compounds of the formulaMpTi.sub.m X.sub.(n. m) +pin which M is an alkaline metal or the group NR.sub.4 in which the valences of the quaternary nitrogen atom are satisfied by hydrogen and/or by hydrocarbon groups or is part of a heterocyclic ring; X.sub.n. m substituents are NR.sub.2 group in which the Rs represent hydrogen, and/or hydrocarbon groups or, in part, halogen atoms; n is the titanium valence; m is a whole number from 1 to 3 inclusive; and p is zero or a whole number from 1 to 3, inclusive; with (2) carriers consisting of anhydrous Mg halides which are in active form or converted to active form by the conditions under which the carriers are contacted with the titanium compounds.