The cationic polymerizations of isobutylene(IB) coinitiated by AlCl_3 were carried out in solvent mixture of n-hexane /methylene dichloride(n-hex/CH_2Cl_2) of 60/40 V/V in the presence of ethyl benzoate(EB) at various temperatures range from-80℃to-30℃.The effects of EB concentration([EB]) and polymerization temperature on monomer conversion,weight-average molecular weight(M_w) and molecular weight distribution(MWD,M_w/M_n) of polyisobutylene (PIB) products were investigated.The rate of polymerization decreased while M_w of PIB products increased with increasing [EB].The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB.Significantly, the polymers with high M_w of 80.2×10~4 and 65.4×10~4 could be produced at-80℃and-70℃at[EB]=0.24×10~(-3) mol/L respectively,which were much higher than that(M_w=57.9×10~4) of PIB prepared at-100℃in the absence of EB.A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work.It has been also found that the activation energy for propagation(E_p) depended on the polymerization temperature range in the presence of EB.An obvious inflection of the linear plots of lnX_n versus 1/T_p occurred at the temperature range from-60℃to-50℃at four different concentrations of EB from 0.19×10~(-3) mol/L to 0.33×10~(-3) mol/L,and thus the inflection temperature(T_(inf)) was in the range of-60℃to-50℃.When[EB]was in the range of 0.24×10~(-3) mol/L to 0.33×10~(-3) mol/L,E_p was determined to be around-12 kJ/mol when the polymerization was carried out at temperatures from-80℃to T_(inf) and to be around-28 kJ/mol at temperatures from T_(inf) to-15℃respectively. The cationic polymerizations of isobutylene (IB) coinitiated by AlCl_3 were carried out in a solvent mixture of n-hexane / methylene dichloride (n-hex / CH_2Cl_2) of 60/40 V / V in the presence of ethyl benzoate range from -80 ° C. to -30 ° C. The effects of EB concentration ([EB]) and polymerization temperature on monomer conversion, weight-average molecular weight (M_w) and molecular weight distribution (MWD, M_w / M_n) of polyisobutylene ) polymers were investigated. The rate of polymerization was decreased while M_w of PIB products increased with increasing [EB]. The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB.Significantly, the polymers with high M_w of 80.2 × 10 ~ 4 and 65.4 × 10 ~ 4 could be produced at -80 ℃ and -70 ℃ at [EB] = 0.24 × 10 -3 mol / L respectively, which were much higher than that (M_w = 57.9 × 10 ~ 4) of PIB prepared at-100 ° C in the absence of EB. A simple but effective method for preparing the high molecular weight polyisobuty lenes was developed in this work. It has been found that the activation energy for propagation (E_p) depended on the polymerization temperature range in the presence of EB. An inflection of the linear plots of lnX_n versus 1 / T_p occurred at the temperature range from -60 ° C. to -50 ° C. at four different concentrations of EB from 0.19 × 10 -3 mol / L to 0.33 × 10 -3 mol / L, and thus the inflection temperature (T inf, was was used in the range of -60 ℃ to-50 ℃ .When the EB was was ranged from 0.24 × 10 -3 mol / L to 0.33 × 10 -3 mol / L, E_p was determined to be around-12 kJ / mol when the polymerization was carried out at temperatures from -80 ° C to T_ (inf) and to be around-28 kJ / mol at temperatures from T_ (inf) to -15 ° C respectively.