Investigation of the photoactivated frontal polymerization of oxetanes using optical pyrometry

An investigation of the photoactivated cationic ring-opening frontal polymerization of a series of 3,3-disubstituted oxetanes was carried out with the aid of a novel technique, optical pyrometry. Using this technique, the effects of various experimental parameters such as photoinitiator type and concentration, light intensity and sample configuration as well as the effects of monomer structure on the frontal behavior of these monomers were examined. Upon photoactivation with UV light, 3,3-disubstituted oxetanes display a long dormant period at room temperature as the result of the formation of metastable tertiary oxonium ions. Only small amount of thermal activation energy is required to induce the further reaction of these species with resulting exothermic autoaccelerated ring-opening polymerization. Frontal polymerization was observed for both mono- and difunctional oxetane monomers and the velocity of propagation of a given monomer was found to be related to its oxetane equivalent weight.