The cationic polymerizations of isobutylene (IB) with H2O/FeCI3/dialkyl ether initiating system were conducted in dichloromethane (CH2Cl2) at temperatures from -20 to +20 degrees C, in which the dialkyl ether includes diethyl ether (Et2O), dibutyl ether (Bu2O) or diisopropyl ether (iPr(2)O). The highly reactive polyisobutylenes (HRPI I3s) with high content of exo-olefin end groups (-CH2 -C(CH3)=CH2) 82-91 mol (parts per thousand) and acceptable monornoclal molecular weight distribution (M-w/M-i = 1.7-2.3) could be successfully synthesized at low concentration of FeCI3 at 0.005 mol L-1 at 0 or even 10 degrees C. These results are comparable to those of commercial HR.PIBs produced industrially at far below 0 degrees C. The directly rapid beta-proton elimination from CH3 of the growing chain ends and chain transfer reaction to monomer were dependent on concentration of iPr(2)O.FeC13 complex (1:1), concentration of free iPr(2)O ([free iPr(2)O] = [iPr(2)O] [FeCI3]) if (iPr(2)O. FeCI3> 1) and polymerization time. The much higher concentration of PIB chains formed in the polymerization system (C-pib) than that of components in initiating system indicates a chain-transfer dominated caionic polymerization process. To the best of our knowledge, this is the first example to achieve HRPIBs with such high exo-olefin end groups by FeC13-based initiating system.