The carbocationic polymerization of styrene(St)initiated by using H2O／TiCl4 was conducted at-60℃ in dichloromethane(CH2Cl2)／hexane(n—Hex)(40／60

V／V)in the presence of pyridine(Py)．The effect of Py

H2O and TiCl4 concentrations on the polymerization rate

molecular weight and molecular weight distribution(MWD or Mw／Mn) of polystyrene(PS)were investigated in detail．The results show that a desirable polymerization process with a relatively slow polymerization rate and PS products with relatively narrow molecular weight distribution (MWD

Mw／Mn≈1．8)were obtained in the presence of a small amount of Py．The polymerization rate and molecular weight of PS obviously decreased while MWD maintained almost unchanged(Mw／Mn≈1．8)with the increase of Py concentration．The kinetic order with respect to Py concentration was calculated to be-0 72 on the basis of flint—order dependence of polymerization rate on monomer concentration．The polymerization rate increased

but the molecular weight of PS products decreased with increasing H2O concentration in the polymerization system．The kinetic order with respect to H2O concentration was calculated to be 0．72 on the basis of first—order dependence of polymerization rate on monomer concentration．Both the polymerization rate and the molecular weight of PS products increased greatly with the increase of TiCl4 concentration and a near second-order(β=1.86)dependence on TiCl4 concentration was observed

which may be attributed to the dimer formation of TiCl4．The experimental resuhs also showed that the monomer conversion as well as the molecular weight of polymer products increased．but MWD almost kept unchanged with the polymerization time．The number—average molecular weight of polymers increased linearly with monomer conversion．