Effective cationic addition polymerization of 1,4-dioxene, a six-membered cyclic olefin with two oxygen atoms adjacent to the double bond, was performed using a simple metal halide catalyst system in dichloromethane. The polymerization was controlled when the reaction was conducted using GaCl3 in conjunction with an isobutyl vinyl etherHCl adduct as a cationogen at 78 degrees C to give polymers with predetermined molecular weights and relatively narrow molecular weight distributions. The long-lived properties of the propagating species were further confirmed by a monomer addition experiment and the analyses of the product polymers by 1H NMR and MALDITOFMS. Although highly clean propagation proceeded, the apparent rate constant changed during the controlled cationic polymerization of 1,4-dioxene. The reason for the change was discussed based on polymerization results under various conditions. The obtained poly(1,4-dioxene) exhibited a very high glass transition temperature (Tg) of 217 degrees C and unique solubility. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012