Syndiospecific styrene (St) polymerization, catalyzed by the CpTiCl3/methylaluminoxane (MAO) system, was investigated using two different activation procedures. The polymerization parameters included polymerization time, temperature (similar to25-100degreesC), ratio of [Al]/[Ti] (similar to100-1000), and catalyst precursor concentration (similar to0.5-10.0 x 10(-4) mol Ti/L). It was found that adding reactants in the order of (CpTiCl3 + MAO) + St (Injection of Styrene mode) gave much higher monomer conversion rates, higher weight-average molecular weights, and narrower molecular weight distributions than for the (St + MAO) + CpTiCl3 (Injection of Catalyst mode). The former also yielded significantly higher syndiotacticity fractions. Differential scanning calorimetry measurements showed multiple peaks exhibiting polymorphism in crystalline syndiotactic polystyrene samples. (C) 2004 Wiley Periodicals, Inc.