Effects of composition and reactivity on the reaction kinetics of dimethacrylate dimethacrylate copolymerizations

The bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxy)phenyl]propane) and TEG D-MA (triethylene glycol dimethacrylate) copolymerization has been often us ed as the organic phase of dental composites and is a good example of a dim ethacrylate/dimethacrylate polymerization involving a viscous monomer and a reactive diluent. This work focuses on the kinetic behavior of this monome r system and the effect of monomer structure, viscosity, and comonomer conc entration on the mobility and reactivity of the evolving network. Unsteady- state polymerizations were performed using various compositions of bis-GMA/ TEGDMA to obtain the kinetic parameters as a function of double-bond conver sion. Furthermore, TEGDMA and bis-GMA were hydrogenated, i.e., the double b onds were saturated, and utilized to study the effect of each reactive comp onent on the copolymerization. The results suggest that reaction diffusion- controlled termination dominates as the reaction progresses and that bis-GM A plays a more controlling role in the kinetics than TEGDMA. In addition, t he hydrogenated monomers were used to determine the effect of viscosity on the homopolymerization of dimethacrylates. It was shown that the addition o f a solvent, i.e., hydrogenated TEGDMA, to the bis-GMA system had a more pr onounced effect on the polymerization kinetics than TEGDMA polymerized in t he presence of viscous hydrogenated bis-GMA. The difference in the kinetic behavior was attributed to the relative mobilities of each monomer.