A kinetic study of the living carbocationic polymerization of isobutylene using a 1,4-bis(2-chloro-2-propyl)benzene (dicumyl chloride) (DCC)/TiCl4 initiating system in conjunction with pyridine as an externally added Lewis base, in mixed hexane/methyl chloride cosolvents was conducted utilizing a wide variety of conditions. The investigation revealed that at -80 degrees C the rate of polymerization was first-order in monomer concentration, first-order in the concentration of the initiator DCC, and second-order in coinitiator (TiCl4) concentration and was proportional to the -0.28 power of the pyridine concentration. In addition, the rate of polymerization was found to decrease with increasing temperature and to increase with increases in solvent polarity. It was also revealed that only ion-paired chain carriers participate in propagation. These results are consistent with a mechanism in which propagation is a simple bimolecular reaction between active polyisobutylene (PIB) chain ends and monomer, and the concentration of active PIB chains is determined by an equilibrium between active and dormant species.