Ethylene polymerization and ethylene-1-hexene copolymerization over immobilized metallocene catalysts

Ethylene polymerization and ethylene-1-hexene copolymerization in the presence of metallocene catalysts based on Cp2ZrCl2, rac-Et(Ind)2ZrCl2, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2, and rac-Me2Si(2-Me-4-Ph-Ind)2HfCl2 been investigated. The catalysts have been immobilized on montmorillonite (MMT) containing methylaluminoxanes (MMT-H2O)/AlMe3 or isobutylaluminoxanes (MMT-H2O)/ Ali-Bu3 synthesized directly on the support surface. The immobilized catalysts, with the general formula (MMT-H2O)/AlR3/Zr(Hf)-cene, show a high activity comparable with the activity of the respective homogeneous systems, which depends on the nature of the metal and on the metallocene composition and structure. The catalytic properties of the metallocene systems depend strongly on the nature of the activator as a component of the catalytic complex. (MMT-H2O)/Ali-Bu3 is a more effective activator of the hafnocene precatalyst in the polymerization processes than oligomeric methylaluminoxane or methylaluminoxane synthesized on the support. The immobilization of the metallocenes on (MMT-H2O)/AlR3 leads to an increase in the molar mass of polyethylene and ethylene-1-hexene copolymers relative to the molar mass of the polymers synthesized using the respective homogeneous systems. The immobilized metallocene catalysts display high selectivity toward the insertion of a higher α-olefin (1-hexene) into the polymer chain, retaining this important property of their homogeneous counterparts.