Oxidation States of Active Species for Syndiotactic-Specific Polymerization of Styrene

Five η 5-L-TiCl3 catalyst precursors, where L is Cp, substituted Cp, Ind, or substituted Ind, having differing resistance to reduction, have been activated by methylaluminoxane (MAO) under identical conditions. Their activities for syndiotactic-specific styrene polymerization and the concentrations of Ti(III) species under polymerization conditions as determined by electron paramagnetic resonance (EPR) have been measured and compared. A linear but inverse relationship was obtained for log(activity) vs log[(%Ti = Ti(III))], with the precursor most resistant to reduction having the highest activity. The results indicate that both η5-L-Ti+(IV)L‘P and η5-L-Ti+(III)P intermediates, where P is the propagating chain and L‘ is Cl or CH3, catalyze styrene polymerization, with the former being 10−20 times more active than the latter.