The polymerization behavior and reaction kinetics for a series of multifunctional (meth)-acrylate monomers were experimentally characterized and modeled with particular attention focused on the importance of the reaction diffusion mechanism in these polymerizations. In general, reaction diffusion was found to be the primary mechanism for termination beginning as low as 5% double-bond conversion. Termination mechanisms in linear systems have been found to become reaction diffusion controlled, but not until much higher conversions, 40-50%. Evidence of reaction diffusion included a significant plateau in the termination kinetic constant and strict proportionality of k , and kt at higher conversion (>lo%) for all monomers studied. The ratio of kt to k , was found to be a single constant for all multiacrylates, independent of the number of acrylate groups. A model that was previously developed by the authors for predicting cross-linking reaction behavior was tested using this experimental data. The kinetic constants for termination and propagation that were experimentally determined provided a method for quantifying the theoretical model parameters associated with reaction diffusion.

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One of the most common combinations for the organic phase of dental restorative materials is BisGMA (2,2bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]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 to be improved, an attempt must be made to understand the underlying kinetics of the reaction. This work examines the effects of light intensity, temperature, and composition on the polymerization behavior of BisGMA/TEGDMA copolymerizations. Using differential scanning calorimetry, we monitored the rates 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 light, and the temperature of the polymerization affected the conversion at which the maximum rate occurred. When the composition of the mixture was varied, it was discovered that the viscosity of the system played a significant role in the polymerization rate and the onset of reaction-diffusion-controlled termination. Mixtures which contained from 50 wt% to 75 wt% BisGMA displayed 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, based on compositional dependence, we conclude that the BisGMA portion of the mixture largely controls the polymerization mechanisms and kinetics.

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