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 (k) and the order of the initiation reaction (m)-were determined for hybrid organicinorganic nanocomposite systems containing different amounts of added silica nanoparticles (0 -20 wt %) and at different isothermal temperatures (30 -100°C) 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.

Summary: This paper reports on the photocuring kinetics of protonic‐acid‐initiated cationic polymerizations of UV‐curable epoxy‐based SU8‐negative photoresist systems with and without silica nanoparticles, as assessed using photo‐DSC, FTIR spectroscopy, UV‐vis spectroscopy, and SEM. Photo‐DSC analysis using an autocatalytic kinetic model demonstrated that the cross‐link density and cure rate increased as the concentration of silica nanoparticles with surface silanol groups increased to 2.5 wt.‐%. This result was confirmed by FTIR spectroscopy, and suggests that the presence of silica nanoparticles of up to 2.5 wt.‐% promoted the cure conversion and cure rate of the UV‐curable hybrid organic/inorganic negative photoresists due to the synergistic effect of silica nanoparticles acting both as an effective flow or diffusion‐aid agent and as a proton‐donor cocatalyst during the cationic photopolymerization process. The decrease in the cross‐link density that occurred when the silica content was higher than 2.5 wt.‐% was attributed to aggregation between silica nanoparticles due to their high surface energy.SEM photograph at the film‐air interface of the UV‐cured hybrid organic/inorganic photoresist containing 10 wt.‐% silica nanoparticles.magnified imageSEM photograph at the film‐air interface of the UV‐cured hybrid organic/inorganic photoresist containing 10 wt.‐% silica nanoparticles.

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