The mechanistic roles of nucleophiles in living carbocationic polymerization of isobutylene were reviewed.There are4mechanisms: A.The "carbocation stabilization" -nucleophiles and/or their complexes with Lewis acid interact with the growing chain end to reduce its "cationicity" and the reduction in cationicity to decrease the polymerization rate

suppress chain transfer and termination reactions; B.The "proton-scavenging" - the removal of protic impurities by externally added nucleophiles and the elimination of "induced" chain transfer; C.The "apparent stabilization of the growing chain ends" - the reduction in the instantaneous carbocation concentration; D.The "suppression of free ions" - the common ions in situ production via the scavenging of protic impurities.