A novel simple but effective initiating system of H,2,O/AlCl,3,/veratrole (VE) has been developed to synthesize high molecular weight polyisobutylene (PIB) at elevated temperatures via cationic polymerization of isobutylene (IB) in solvent mixture of hexane/methylene dichloride (,n,-Hex/CH,2,Cl,2, = 2/1,V,/,V,). VE played very important roles in decreasing cationicity of the growing chain ends, suppressing side reactions of chain transfer and termination during polymerization, leading to production of high molecular weight PIBs. PIBs with high yields, having very high weight-average molecular weight (,M,w,) of 1117000 and 370000 g/mol could be synthesized with H,2,O/AlCl,3,/VE initiating system at VE concentration of 5.4 mmol/L at −80 and −60℃ respectively. Molecular weight of PIB increased remarkably with increasing VE concentration. The reaction order with respect to VE concentration was determined to be −3.52 ,via, FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe. The negative reaction order of VE was consistent with its retarding effect on IB polymerization by interacting with the propagating species. Molecular weight of PIB decreased with increasing polymerization temperature. The activation energy for polymerization degree (,E,DP,) could be determined to be around −23 kJ/mol when VE concentration was 5.4 mmol/L or 6.4 mmol/L.