Preparation and properties of crystalline polystyrene: II. Effects of polymerization conditions

For styrene polymerization initiated by using a half-sandwich titanocene catalyst such as cyclopentadienyltitanium trichloride (CpTiCl₃), indenyltitanium trichloride (IndTiCl₃) or pentamethylcyclopentadienyltitanium trichloride (Cp*TiCl₃) with modified methylaluminoxane (MMAO) cocatalyst, the effects of polymerization conditions on polymerization behavior and properties of polystyrene were examined. With increasing MMAO concentrations, the catalyst activity increased and the molecular weight (MW) of polystyrene (PS) decreased. The catalyst activity of Cp*TiCl₃ increased up to 80°C, while CpTiCl₃ and IndTiCl₃ gave maximum catalyst activity at 30 and 40°C. MW and syndiotactic index (SI) of PS decreased with increasing polymerization temperature. The polydispersity of PS was less dependent on polymerization conditions. By increasing styrene concentration, the catalyst activity and MW of PS increased. For IndTiCl₃, the catalyst activity and MW of PS were promoted with a short aging time. Irrespective to polymerization conditions, Cp*TiCl₃ gave high catalyst activity and the obtained PS had high SI, MW, and melting temperature.