Living carbocationic polymerization of isobutylene (IB) was achieved by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl 4 initiating systems in the presence of KCl in conjuction with the 18-crown-6 ether in CH 2 Cl 2 /hexanes solvent mixture at -80°C; The rate of initiation is relatively slow and the molecular weight distribution of the polymer becomes narrower (from ∼1.8 to ∼1.2) in the course of incremental monomer addition. In the presence of the crown ether and depending on its concentration the charges become highly viscous preventing the synthesis of M n 's in excess of 15000