No abstract

Summary: A new procedure was developed to support [(ArNC(Me))2C5H3N]FeCl2 (Ar2,4,6‐trimethylphenyl) on spherical MgCl2 for ethylene polymerization. The resultant catalysts showed ten times higher activity of the corresponding catalyst in homogeneous catalysis. The morphologies of polyethylene particles strongly depended on supported catalyst preparation procedure and polymerization conditions. In addition, the GPC measurements showed bimodal polyethylene for the homogeneous polymerization while mono‐modal polyethylene of those supported catalysts.EDX Line Scan analysis of the catalyst SMSIC‐1 regarding the aluminium and iron distribution in the volume (25 kV accelerating voltage, magnification 1 500).imageEDX Line Scan analysis of the catalyst SMSIC‐1 regarding the aluminium and iron distribution in the volume (25 kV accelerating voltage, magnification 1 500).

The ability of a MgCl2 support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu2 with HCl gave high activity with TiCl4 but low activity with (n‐PrCp)2ZrCl2. High polymerization activities with the zirconocene were only obtained with supports of type MgCl2/AlRn(OEt)3−n prepared from the reaction of AlR3 with MgCl2 · 1.1EtOH. These supports are characterized by additional peaks in the X‐ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species.magnified image

Significant increases in the productivity of iron-, chromium-, and titanium-based MgCl2-supported catalysts for ethylene polymerization have been obtained by incorporation of a limited amount of a nickel diimine catalyst giving branched polyethylene. Formation of the latter during the early stages of polymerization reduces the monomer diffusion limitation inherent in ethylene homopolymerization, thereby increasing the productivity of the main catalyst component. The final products are essentially linear, high-density polyethylenes containing very small amounts of branched polymer. As well being effective for catalysts prepared 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 polymerization indicated easier fragmentation of the support in the presence of the nickel complex.