SUPPORTED TRANSITION-METAL COMPLEXES FOR ETHYLENE POLYMERIZATION

This paper describes the preparation of some active organometallic spe cies derived from nickel, titanium and zirconium fixed on the surface of different supports and their behaviour for the catalytic polymeriza tion of ethylene. In the case of nickel, the transition metal species were attached to crosslinked polystyrene resins through a carbon atom of the P/O chelate ligand. The formation of high molecular weight line ar polyethylene is discussed in comparison to homogeneous analogs givi ng oligomeric products under the same conditions. Titanium containing species on the MgCl2 surface are obtained by coprecipitating the metal s from solution of their alcoholates or carboxylates. These species ar e shown to be sensitive to the presence of carboxylate ligands which a ffect the catalytic process. Finally biscyclopentadienyl dichloro or d imethyl zirconium have been supported on modified HY zeolite to give c atalysts showing the same activity as the homogeneous analogs but high er stability during the polymerization reactions. General aspects deri ving from these results are discussed with reference to the possibilit y of improving the design of well defined physically heterogeneous cat alysts.