Radiation‐induced solid‐state polymerization of ring compounds

Ring compounds such as trioxane, β-propiolactone, diketene, and 3,3-bischloromethylcycloxabutane can be polymerized only in the solid state by γ-radiation. These ring compounds polymerize by a ring-opening, ionic mechanism to highly crystalline, high molecular weight, linear polymers. In general, the conversion vs. irradiation time curves reach a limiting value at relatively low yield. These saturation phenomena are due to the disruption of unreacted monomer lattice by the formed polymer. The polymers obtained from large-monomer crystals are found to have outward appearances of large crystals which suggest the monomer crystalline lattice has influenced that of the polymer. Moreover, the polymers from large crystalline monomer have higher polymerization rate and better orientation of the crystallites, as ascertained through x-ray diffraction and polarizing microscopic analyses. Polarizing microscopic photographs of the polymers show birefringence clearly. These facts indicate that the structure of the monomer lattice directly imposes order and orientation upon the polymer. X-ray diffraction analyses show that the polydiketene chain has a spiral configuration and poly-β-propiolactone has a planar zigzag chain. Some consideration of the propagation mechanism in the crystalline state of 3,3-bischloromethylcycloxabutene, γ-propiolactone, diketene, and trioxane is made. Investigations of the binary systems with β-propiolactone were carried out to determine the effects of additives upon the propagation mechanism.