Model for the Effects of Water on the Cationic UV-Curing of Cyclohexyl Epoxides

By Mark D. Soucek, Jianxia Chen

The effect of relative humidity on the photoinduced curing kinetics of cyclohexyl epoxide and epoxide/polyol coating formulations was investigated in real-time using FTIR spectroscopy. In total, five formulations were used in this study, including a cyclohexyl epoxide without polyol, and four with polyols. The polyol formulations were varied with respect to ratio of epoxide to polyol, and molar functionality of the hydroxyl group.

The formulations were exposed to a maximum of seven different relative humidities (6, 16, 20, 30, 51, 62, 75 RH). The curing speed and overall conversion of the epoxy group passed through a maxima for all the formulations. The polyol had an effect on the hydrophilicity of the overall formulation.

It was also found that water and polyols had a synergistic effect on the UV-curing kinetics, in effect lowering the relative humidity to achieve a maxima. A model for UV-curing mechanisms at low, medium, and high relative humidity was proposed for both systems with and without the polyols.