Effect of substituents on the catalytic properties of bis(cyclopentadienyl)zirconium dichloride complexes with polymethylaluminoxane and AlBu3i/CPh3B(C6F5)(4) cocatalysts in ethylene polymerization

The catalytic properties of the complexes (RCp)(2)ZrCl2 (R = H, Me, Pr-i, B u-n, Bu-i, Me3Si, cyclo-C6H11), and Me2SiCp*(NBuZrCl2)-Zr-t (Cp* = C-5(CH3) (4)) combined with the AlBu3i-CPh3B(C6F5)(4) cocatalyst in ethylene polymer ization were studied. The specific activity of the substituted bis-cyclopen tadienyl complexes decreases in the sequence: Me > Pr-i > Bu-n > Bu-i > Me3 Si > cyclo-C6H11, which corresponds to the activity sequence for these comp lexes activated by polymethylaluminoxane (MAO) but is 4-20 times lower in a bsolute value. Comparison of the polyethylene samples obtained in the prese nce of the same complexes with MAO and AlBu3i-CPh3B(C6F5)(4) cocatalysts sh owed that polyethylene with much higher molecular mass, melting point, and crystallinity is formed in the presence of the ternary catalytic systems, a nd this indicates a different nature of the active sites of the catalytic s ystems. The effective activation energy of polymerization (similar to 3.6 k cal mol(-1)), first order with respect to monomer and similar to 0.4 order with respect to organoaluminum component, was found for the ((PrCp)-Cp-i)(2 )ZrCl2-AlBu3i-CPh3B(C6F5)(4) catalytic system. It was proposed on the basis of the kinetic data that (AlBu3)-Bu-i enters into the composition of the a ctive site to form a bridged heteronuclear cationic complex.