Photoinitiated polymerization of a dental formulation, part 2: kinetic studies

This work examines the classic dental formulation of dimethacrylate resins Bis-GMA and TEGDMA with camphorquinone (CQ)/N,N-dimethylaminoethyl methacrylate, which is recognized as the most efficient photoinitiator system for this type of formulation. The kinetics of photoinitiated polymerization of this formulation was studied using isothermal photocalorimetry. Two kinetic models were applied. First, it is shown that an autocatalytic model can describe the reaction satisfactorily. As long as the reaction system has not reached its freezing point, the reaction follows the autocatalytic pattern perfectly. The analysis of the linear part of the curve then allows us to obtain the values of the coefficients m = 0.4 and n = 1.6. The reaction temperature does not influence the orders m and n of the reaction, but the phenomenological rate constant k varies with temperature according to the Arrhenius law up to 60 °C. In addition, the ratio of the rate constants k and k were calculated by means of a mechanistic model. Their evolution with conversion has been studied for different reaction temperatures, and the results effectively illustrate the importance of the reactive diffusion mechanism.