Synergetic effect of a nickel diimine in ethylene polymerization with immobilized Fe-, Cr-, and Ti-based catalysts on MgCl2 supports

Significant increases in the productivity of iron-, chromium-, and titanium-based MgCl2-supported catalysts for ethylene polymn. have been obtained by incorporation of a limited amt. of a nickel diimine catalyst giving branched polyethylene. Formation of the latter during the early stages of polymn. reduces the monomer diffusion limitation inherent in ethylene homopolymn., thereby increasing the productivity of the main catalyst component. The final products are essentially linear, high-d. polyethylenes contg. very small amts. of branched polymer. As well being effective for catalysts prepd. by coimmobilization of the Ni and Fe, Cr, or Ti component on the MgCl2 support, it is also shown that the productivity of preformed Ziegler-Natta catalysts can be improved significantly by impregnation with the nickel diimine component. In the latter case, more rapid increases in rate throughout the polymn. indicated easier fragmentation of the support in the presence of the nickel complex.