A comparative study was performed on the radiation postpolymerization of a number of dienes and α-olefins with sulfur dioxide occurring both on heating of the samples radiolyzed at 77 K and spontaneously by mutual dissolution. The cryopolymerization of sulfur dioxide with butadiene was studied in most detail. It was found that, unlike the case of the isoprene–SO2system, a polycrystalline phase with the eutectic that corresponded to the equimolar composition was formed on rapidly freezing over the entire range of initial ratios between the butadiene and SO2comonomers. It was suggested that the 1 : 1 donor–acceptor complex takes part in the postpolymerization process, and the monomers enter the resulting copolymer in a near-equimolar ratio. The copolymer obtained was found to behave as a crosslinked system. It is likely that a three-dimensional network resulted from the opening of C=C bonds in butadiene.