| abstract |
Disclosed is for the preparation of a catalytic composition for the polymerization of alpha-olefins. The catalyst comprises a compound of a transition metal (i) of Groups 4 to 6 of the Periodic Table, containing at least one possibly substituted cyclopentadiene ligand, and an activator (ii) chosen from aluminoxanes and ionizing agents supported on a support (iii) consisting of porous particles of polyolefin(s). Preparation includes a preliminary polymerization which includes contact with an alpha-olefin, under polymerizing conditions, in a diluent whose kinematic viscosity, measured at 20° C., is from 3 to 3000 cSt (centistokes) from 3 to 3000 mm2/s, such as mineral oil which may be derived from coal tars and petroleum fractions, to form from 0.01 to 50 g of polyolefin per g of catalyst containing compounds (i), (ii) and (iii). |