The carbocationic polymerization of styrene(St)initiated by H2O／TiCl4 system was conducted at-60℃ in dichloromethane(CH2Cl2)／hexane(n-Hex)(50／50 V／V)in the presence of pyridine(Py)

2-methyl pyridine (Mry)and 2

6-dimethyl pyridine(DMPy)．A desirable polymerization process with a relative slow polymerization rate and PS products with relatively narrow molecular weight distribution(MWD

Mw／Mnca．1．8)were obtained．Py and its derivants and／or their complexes with Lewis acid TiCl4 interact with the growing chain end to reduced its “eationieity”and thus to decrease the polymerization rate

suppress chain transfer and termination reactions and narlow MWD．The experimental results also show that the monomer conversion as well as the molecular weisht of polymer products increased but MWD almost kept unchanged with polymerization time．The number-average molecular weight of polymer increased linearly with monomer conversion but the line did not pass through the origin．