The bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxy)phenyl]propane) and TEGD-MA (triethylene glycol dimethacrylate) copolymerization has been often used as the organic phase of dental composites and is a good example of a dimethacrylate/dimethacrylate polymerization involving a viscous monomer and a reactive diluent. This work focuses on the kinetic behavior of this monomer system and the effect of monomer structure, viscosity, and comonomer concentration 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 conversion. Furthermore, TEGDMA and bis-GMA were hydrogenated, i.e., the double bonds were saturated, and utilized to study the effect of each reactive component on the copolymerization. The results suggest that reaction diffusion-controlled termination dominates as the reaction progresses and that bis-GMA plays a more controlling role in the kinetics than TEGDMA. In addition, the hydrogenated monomers were used to determine the effect of viscosity on the homopolymerization of dimethacrylates. It was shown that the addition of a solvent, i.e., hydrogenated TEGDMA, to the bis-GMA system had a more pronounced effect on the polymerization kinetics than TEGDMA polymerized in the presence of viscous hydrogenated bis-GMA. The difference in the kinetic behavior was attributed to the relative mobilities of each monomer.