ANSA-ZIRCONOCENE POLYMERIZATION CATALYSTS WITH ANNELATED RING LIGANDS - EFFECTS ON CATALYTIC ACTIVITY AND POLYMER-CHAIN LENGTH

The dimethylsilyl-bridged zirconocene complexes (CH3)2Si(benz[e]indenyl)2ZrCl2 (I) and (CH3)2Si(2-methylbenz[e]indenyl)2ZrCl2 (II) have been synthesized; the structure of II was determined by X-ray diffraction. Complex I is about 4 times more active in polymerizing propene than its bis(indenyl) analog when activated with methylaluminoxane (MAO) under otherwise identical conditions. The resulting catalyst system polymerizes also the gamma-branched olefins 3-methyl-1-butene and 3-methyl-1-pentene. Polymers produced with complex II have molecular weights about 4 times higher than those obtained with complex I under identical conditions. The alpha-methyl substituents of II appear to block those chain terminations which arise from beta-H transfer directly to a coordinated monomer molecule.