Syndiospecific Styrene Polymerization Promoted by Half-Titanocene Catalysts:  A Kinetic Investigation Providing a Closer Insight to the Active Species

Syndiospecific styrene polymerization promoted by mixtures of Cp*TiR 3 (R = CH 3, CH 2 Ph) with MAO, B(C 6 F 5 ) 3, and CPh 3 B(C 6 F 5 ) 4 has been investigated by means of conventional kinetic methods. A first-order kinetics of the monomer in the propagation rate has been determined at 25 °C. At polymerization temperatures higher than 50 °C, the β-H migration from the growing polymer chain to the metal of the active species appears to be the main termination reaction. The average molecular weights of the polymer products depend on the type and coordinating behavior of the counterions ([MAOX] -, [MeB(C 6 F 5 ) 3 ] -, [(PhCH 2 )B(C 6 F 5 ) 3 ] - ). The trityl-activated catalysts produce sPS samples with the highest molecular weights. The comparison of the molar concentrations of the active species, determined by kinetic methods, with those of Cp*Ti III R + (R = CH 3, CH 2 Ph) evaluated in the polymerization conditions by ESR measurements, confirms the involvement of these complexes in syndiospecific styrene polymerization.