Hybrid Free-Radical/Cationic Phase-Separated UV-Curable System:Impact of Photoinitiator Content and Monomer Fraction on SurfaceMorphologies and Gloss Appearance

Simultaneous photopolymerization of radical and cationic systems is one strategy to generate polymer networkarchitectures named interpenetrating polymer networks (IPNs). In these hybrid systems, phase separation andfinal polymermorphology are ultimately governed by thermodynamic incompatibility and polymerization kinetics. This behavior is quite complex,as numerous factors can affect polymerization kinetics including monomer/oligomer viscosity and structure, light intensity,photoinitiator content and absorbance, cross-linking, vitrification, etc. In this work, the impact of photoinitiator concentration andmonomer fraction on surface morphologies in a hybrid radical/cationic phase-separated system was examined. Wrinkles formed onthe surface of photopolymerizedfilms depend on the polymerization rate and acrylate/epoxy ratio. This phenomenon is partiallyexplained by the rapid polymerization rate associated with the development of an epoxy matrix and a smaller acrylate domain. Thesize and shape of the wrinkles can be controlled by varying formulation parameters (mainly, composition) and photoinitiatorcontent. It was possible to create surface roughness and consequently decrease the gloss by controlling the polymerization kineticsand phase-separated morphology. This study demonstrates that the morphology, polymerization kinetics, andfilm properties (e.g.,gloss, transparency) can be manipulated with the ratio of the acrylate/epoxy mixture and the photoinitiator content.