We synthesized the alternating copolymers of 1,3-diene monomers with sulfur dioxide (SO 2 ) as a new class of thermally stable polymers by the radical copolymerization process and the subsequent hydrogenation. The copolymerizations of 2,4-hexadiene (HD), 1,3-butadiene (BD), and isoprene (IP) with SO 2 were carried out at -78 to 0 °C in toluene in the presence of tert-butyl hydroperoxide, which acts as one component in the redox initiating system in combination with SO 2 . The resulting poly(diene-alt-SO 2 )s were found to consist of highly controlled repeating units, that is, an alternating and 1,4-regiospecific repeating structure. Poly(HD-alt-SO 2 ) was soluble in several organic solvents, such as chloroform, nitromethane, tetrahydrofuran, acetone, and dimethyl sulfoxide. In contrast, poly(IP-alt-SO 2 ) was soluble only in dimethyl sulfoxide, whereas poly(BD-alt-SO 2 ) was insoluble in all of the solvents. The poly(diene-alt-SO 2 )s readily degraded upon heating because of the expected fast depolymerization. We have demonstrated that the thermal stability of the poly(diene-alt-SO 2 )s is modified by the hydrogenation of the double bond in the polymer main chain. The hydrogenation of poly(HD-alt-SO 2 ) resulted in a drastic increase in the 5% weightloss temperature from 135 to 317 °C.

Recent progress in optoelectronics has demanded highperformance polymers with excellent thermal stabilities as well as optical, electronic, and other physical properties. Thermally stable aromatic polysulfones are obtained by condensation polymerization and used as engineering plastics for the mechanical

The free-radical copolymerization of alkyl-substituted 1,3-butadienes with sulfur dioxide using a redox initiating system in toluene at -78 °C produced poly(diene sulfone)s consisting of a highly alternating and 1,4-regiospecific repeating structure, irrespective of the position and number of alkyl substituents, and the highly regioselective propagation via a free radical reaction mechanism is well accounted for by DFT calculations using model reactions.