Supported transition metal complexes for ethylene polymerization

This paper describes the preparation of some active organometallic species derived from nickel, titanium and zirconium fixed on the surface of different supports and their behaviour for the catalytic polymerization 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 linear polyethylene is discussed in comparison to homogeneous analogs giving oligomeric products under the same conditions. Titanium containing species on the MgCl2 surface are obtained by coprecipitating the metals from solution of their alcoholates or carboxylates. These species are shown to be sensitive to the presence of carboxylate ligands which affect the catalytic process. Finally biscyclopentadienyl dichloro or dimethyl zirconium have been supported on modified HY zeolite to give catalysts showing the same activity as the homogeneous analogs but higher stability during the polymerization reactions. General aspects deriving from these results are discussed with reference to the possibility of improving the design of well defined physically heterogeneous catalysts.