The effects of light intensity, temperature, and comonomer composition on the polymerization behavior of dimethacrylate dental resins

One of the most common combinations for the organic phase of dental restora tive materials is BisGMA (2,2 bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phe nyl]propane) and TEGDMA (triethylene glycol dimethacrylate). However, this copolymer has some drawbacks, such as volume shrinkage during cure and lack of complete double-bond conversion. If the properties of this system are t o be improved, an attempt must be made to understand the underlying kinetic s of the reaction. This work examines the effects of light intensity, tempe rature, and composition on the polymerization behavior of BisGMA/TEGDMA cop olymerizations. Using differential scanning calorimetry, we monitored the r ates of photopolymerization for various experimental conditions. The BisGMA /TEGDMA copolymerization behaved similarly to other dimethacrylate systems and exhibited diffusion-controlled kinetics. It was found that the maximum rate of polymerization was significantly affected by the intensity of the l ight, and the temperature of the polymerization affected the conversion at which the maximum rate occurred. When the composition of the mixture was va ried, it was discovered that the viscosity of the system played a significa nt role in the polymerization rate and the onset of reaction-diffusion-cont rolled termination. Mixtures which contained from 50 wt% to 75 wt% BisGMA d isplayed the highest maximum rate. This feature suggests that TEGDMA is an excellent diluent, since it increases the mobility of the reacting medium; however, the high reactivity is due to the presence of BisGMA. Therefore, b ased on compositional dependence, we conclude that the BisGMA portion of th e mixture largely controls the polymerization mechanisms and kinetics.