THERMAL ASPECTS OF THE KINETICS OF DIMETHACRYLATE PHOTOPOLYMERIZATION

The photopolymerization kinetics of four bisphenol-A based dimethacrylate resins were studied from -40 to 160-degrees-C by isothermal differential scanning calorimetry. The limiting conversion was low at temperatures near the glass transition temperature (T(g)) of the monomer but increased rapidly as the curing temperature was raised. These data were successfully fitted to a theoretical relationship between curing temperature, conversion and T(g). At higher cure temperatures, the limiting conversion was topologically controlled, in agreement with the Loshaek-Fox theory. The photopolymerization rate increased rapidly to a maximum and then decreased slowly as the monomer was consumed. Using the encounter theory for reaction rates, the kinetics of the propagation and termination steps were expressed by combination of thermal (Arrhenius) and free volume (WLF) terms. These expressions were then combined with the theories of translation and reaction diffusion, allowing the prediction of the temperature dependence of the overall polymerization rate. Despite its simplicity, many of the observed kinetic features were reproduced by the model.