p-Methoxystyrene (MOS) and n-butyl vinyl ether (BVE) were polymerized to high polymer by azo initiators in the presence of Ph(2)I(+)PF(6)(-). The polymer formation shows that the transformation of propagating radical into propagating cation took place in the polymerization process of MOS and EVE. ESR study of the model radicals supports the fact that the transformation of the radical to the corresponding cation occurred in the presence of an electron-transfer reagent. Block copolymers of MOS and cyclohexene oxide (CHO) were effectively prepared by the radical polymerization of MOS in the presence of Ph(2)I(+)PF(6)(-) and CHO. The block copolymerization is ascribable to the transformation of growing ends from radical to cationic species during the propagation step.