In photoinitiated cationic ring-opening polymerization, the polymerizable substrate is subjected to irradiation with light for a brief period during which the photopolymerization must proceed essentially to completion. Consequently, only monomers that undergo very high rates of polymerization may be employed. Certain epoxide monomers display high reactivity in photoinitiated cationic polymerization and are suitable for such uses while most other undergo sluggish reaction and are not usable. Additionally, oxetane monomers are not generally useful by themselves due to their slow photocure rates. This invention is directed to a novel approach for accelerating the polymerizations of all epoxide and oxetane monomers that makes it possible to employ epoxide and oxetane monomers previously thought to be too unreactive for use in a wide variety of applications. Moreover, application of this approach to existing high reactivity monomers provides a further increase in their photocure speed. Because this technology is both easy to implement and low in cost, it has the potential to allow more widespread use of cationic photopolymerizations in such applications as coatings, adhesives, printing inks, and stereolithography.