An investigation of the reactivity of the cycloaliphatic diepoxide, 3,4-epoxycyclohexyl 3’,4’-epoxycyclohexane carboxylate (I) in photoinitiated cationic polymerization was carried out with the aid of model compounds. It was shown that the presence of the ester group greatly retards the rate of polymerization of this bisepoxide. Molecular modeling studies indicate that the ester carbonyl group can interact in a number of ways with the initially formed protonated or alkylated oxiranium cation to give bicylic dialkoxycarbenium ions. These latter species are both more sterically hindered and less reactive than the oxiranium cation precursors and undergo propagation at a considerably reduced rate. Reactivity studies employing model compounds also showed that epoxy monomers that contain ester groups undergo polymerization at much slower rates than those in which the ester group is absent.