Synthesis of epoxy monomers that undergo synergistic photopolymerization by a radical-induced cationic mechanism

A series of novel, cycloaliphatic, cationically photopolymerizable epoxide monomers bearing benzyl ether groups were prepared. These monomers display a considerable enhancement in the rate of their cationic ring-opening polym erizations in comparison with monomers that do not contain such groups. In this article, a synergistic free-radical mechanism is proposed that account s for this effect, and supporting evidence is offered for its verification. During UV irradiation of an onium salt cationic photoinitiator, the aryl r adicals that are generated abstract labile benzyl hydrogens present in such monomers to generate the corresponding carbon-centered radicals. Subsequen tly, these radicals are oxidized to benzyl carbocations by the onium salt v ia a nonphotochemical chain process. The observed increase in the rate and extent of the cationic ring-opening polymerization of the epoxide monomers is due to the aforementioned mechanism, which effectively increases the num ber of reactive cationic species present during polymerization. (C) 2001 Jo hn Wiley & Sons, Inc.