We synthesized the thermally stable alternating copolymers from various acyclic and cyclic alkyl-substituted 1,3-diene monomers with sulfur dioxide (SO2) as the starting comonorners by radical copolymerization and subsequent hydrogenation. It was revealed based on the DFT calculation results using model reactions as well as the thermodynamic analysis of polymerization that some propagation steps were reversible and the highly 1,4-regiospecific sequences of the poly(diene sulfone)s (PDSs) were consequently produced via a free radical propagation mechanism. The stereochemical structures of the PDSs obtained from cyclic 1,3-diene monomers, such as 1,3-cyclopentadiene and 1,3-cyclohexadiene, were also estimated based on the DFT calculations. Transparent films with a refractive index of 1.53-1.55 were readily obtained by casting the PDS solutions, being confmned to be amorphous by wide-angle X-ray diffraction measurements. The decomposition of the PDSs started below 150 degrees C, but hydrogenation produced thermally stable polymers, of which the onset temperatures of decomposition were higher than 280 degrees C. The hydrogenation conversion significantly depended on the position of an alkyl substituent on the polymer main chain. A ternary copolymerization system consisting of both cyclic and acyclic diene monomers with SO2 was carried out in order to simultaneously modify the thermal properties as well as the solubility of the resulting polymers.
