The synthesis of a series of novel cationically photopolymerizable epoxide monomers bearing benzyl, allyl, and propargyl acetal and ether groups that can stabilize free radicals was carried out. These monomers display enhanced reactivity in cationic photopolymerization in the presence of certain onium salt photoinitiators. Specifically, this article describes schemes for the synthesis of cycloaliphatic epoxy monomers bearing free-radical stabilizing groups. During W irradiation of an onium salt cationic photoinitiator, the aryl radicals that are generated abstract labile protons present in such monomers to generate the corresponding carbon-centered radicals. Subsequently, these radicals can interact with the onium salt by a redox mechanism to induce the decomposition of these salts. The overall result is that additional cationic species are generated by this mechanism that increase the rate and extent of the cationic ring-opening polymerization of the epoxide monomer. An investigation of the photopolymerizations of the monomers prepared during this work was carried out using Fourier transform real-time infrared spectroscopy, and conclusions were drawn with respect to the relationship between their structures and reactivity.