Photocuring kinetics of UV-initiated free-radical photopolymerizations with and without silica nanoparticles

We used photodifferential scanning calorimetry to investigate the photocuring kinetics of UV-initiated free-radical photopolymerizations of acrylate systems with and without silica nanoparticles. Two kinetics parameters-the rate constant (h) and the order of the initiation reaction (m)-were determined for hybrid organic-inorganic nanocomposite systems containing different amounts of added silica nanoparticles (0-20 wt %) and at different isothermal temperatures (30-100 degreesC) using an autocatalytic kinetics model. The kinetic analysis revealed that the silica nanoparticles apparently accelerate the cure reaction and cure rate of the UV-curable acrylate system, most probably due to the synergistic effect of silica nanoparticles during the photopolymerization process. However, a slight decrease in polymerization reactivity that occurred when the silica content increased beyond 15 wt % was attributed to aggregation between silica nanoparticles. We also observed that the addition of silica nanoparticles lowered the activation energy for the UV-curable acrylate system, and that the collision factor for the system with silica nanoparticles was higher than that obtained for the system without silica nanoparticles, indicating that the reactivity of the former was greater than that of the latter. (C) 2004 Wiley Periodicals, Inc.