Photoactivated cationic ring-opening frontal polymerizations of oxetanes

The photoinitiated cationic ring-opening polymerizations of 3,3-disubstituted oxetanes display a characteristic induction period followed by very rapid thermally accelerated polymerization. When a thin-film sample of such a monomer is irradiated for a time within the induction period and then allowed to stand at room temperature, no appreciable further conversion of monomer to polymer takes place. However, when heat is applied to a small portion of the films rapid polymerization takes place as a front, which propagates rapidly throughout the entire reaction mass. To characterize these frontal polymerizations, a new monitoring technique, employing optical pyrometry has been instituted. This method provides a simple, rapid means of following these polymerizations and quantitatively determining their frontal velocities.