Influence of the initiating mechanism on the cationic photopolymerization of a cycloaliphatic epoxy resin with arylsulfonium salts

The photocuring process of widely used 3,4‐epoxycyclohexylmethyl 3′,4′‐epoxycyclohexane carboxylate has been investigated with differential scanning photocalorimetry and attenuated total reflection/Fourier transform infrared. Mixed salts of triarylsulfonium hexafluoroantimonate have been employed as the photoinitiator. The photocuring of the biscycloaliphatic resins exhibits a complex behavior: the overall heat of reaction (including dynamic thermal postcuring) depends on the photocuring temperature, surprisingly high reaction rates are observed at lower photocuring temperatures, and the range of the glass transition of the fully cured material broadens and shifts to higher temperatures as the photocuring temperature increases. It is assumed that the balance between the initiation step and the propagation step is responsible for the changes in the reaction mechanism that produce the observed experimental results. This balance may depend on the amount of the photoinitiator, the irradiation intensity, and the photocuring temperature. The structure and final properties of the material may therefore depend on the adjustment of these parameters.