A rapid cationic polymerization of cyclohexene oxide that completed within a few minutes was achieved by a new initiation system that involves (1) a copper-catalyzed reduction of benzoyl peroxide by an ascorbic acid derivative that generates free radicals and (2) capture of the radicals by allyl sulfonium salt having hexafluoroantimonate (SbF6-) as a counter anion, followed by fragmentation of sulfonium radical cation, from which a super acid HSbF6 was produced to initiate the rapid polymerization. The key factor in designing an efficient allyl sulfonium salt was attachment of an electron withdrawing ester group at the allyl group, of which ability to stabilize the formed radical can enhance the efficiency in trapping radicals by the allylic salt. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4178-4183, 2010