The effect of substituents in bis(cyclopentadienyl)zirconium
dichloride complexes on catalytic properties with
Al(i-Bu)3/CPh3B(C6F5)4 as activator in ethylene polymerization
Polimery 2001, No 1, 44
A series of zirconocenes (RCp)2ZrCl2 (R = H, Me, i-Pr, n-Bu, i-Bu, Me3Si, cyclo-C6H11) and a "constrained geometry catalyst” Me2SiCp*N(t-Bu)ZrCl2 (Cp* == C5(CH3)4), activated with Al(i-Bu)3/CPh3B(C6F5)4, were studied in relation to catalytic properties in ethylene polymerization. With varying substituents, the complexes gave polymer yields diminishing in the following descending order: Me > i-Pr > n-Bu > i-Bu > Me3Si > cyclo-C6H11. The logarithm of initial polymerization rate (eqn. 3) was found to be directly related to the superposition of inductive and steric constants of the substituents in the ternary systems (Fig. 3, Table 2). The M of the PE produced with the aid of ternary catalytic systems was higher than that of PE produced with the corresponding complexes using methylaluminoxane (MAO) as cocatalyst. Polymerization kinetics data allow to suggest the Al(i-Bu)3 to have been incorporated into the active center as a heteronuclear bridged complex.
Keywords: polymerization of ethylene, catalyst systems, zirconocenes, polymerization kinetics, catalyst activity