Influence of actinic wavelength on properties of light-cured interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of different acrylate/epoxide ratios, were synthesized under UV and visible-LED curing conditions. The formation of the IPNs was explored in terms of phase separation, polymerization mechanisms, final mechanical properties and surface morphology. For these purpose, we uniquely combined results of miscibility investigations, confocal Raman microscopy, dynamical mechanical analysis and atomic force microscopy. Transparent films were obtained for all compositions and both irradiation sources. The thermo-mechanical properties of different IPNs were associated to the presence of acrylate- or epoxide-rich phases, as well as, mixed interphases, resulting from the high interpenetration between both networks. Although the final conversions were similar under UV and visible-LED irradiation, we have found evidence that the visible-cured samples provide higher IPN homogeneity and lower T_g, for a higher epoxide content. To explain this trend, the mechanisms and sequence of the acrylate or epoxide networks formation, under UV or LED irradiation, is discussed.