The cationic photopolymerizations of monofunctional monomers and cycloaliphatic diepoxide monomer were examined in detail. Phenomenological kinetic models were developed for photopolymerizations of the monofunctional and difunctional monomers. For monofunctional monomers, the nonlinear models gave an excellent fit to the experimental data. Although a second-order autocatalytic model was shown to be invalid above 10% conversion for the polymerization of a difunctional monomer (3,4-epoxycyclohexylmethyl-3',4'-epoxycyclo-hexane carboxylate, ECH), an autocatalytic model using diffusion-controlled reaction with a Williams-Landel-Ferry (WLF) equation fits the experimental data well over the entire conversion range. A mechanistic model based on the free volume theory was also developed for cationic polymerization of the cycloaliphatic di-epoxide monomer by using the method of moments. The model gives a good fit for the conversion and M-w development, but the calculated M-n results are lower than the experimental values.