(273d) Structure-Property Relationships for Epoxide/Acrylate Hybrid Polymers Produced by Photopolymerizations

Photopolymerization method has been widely applied due to its energy savings, solvent-free systems, and ability of reaction control. Hybrid systems containing urethane acrylates and cycloaliphatic epoxides have been studied to mitigate kinetic interruptions by atmospheric factors, namely oxygen and water that affect radical and cationic active species, respectively. In addition, the control of interpenetrating structures (IPNs), produced by combining chemically independent free-radical and cationic polymerizations, was aimed at tuning physical/mechanical properties of final hybrid polymers. However, the formation of acrylate networks preceeds much faster than that of epoxide polymer domains, resulting in the suppression of the epoxide photopolymerizations. To solve this problem, dynamic modulation method was devised to control the degree of acrylate networks and to enhance epoxide kinetics: by manipulating illumination and temperature, the kinetics of epoxides during hybrid photopolymerizations was significantly enhanced. In this study, we investigated the physical and mechanical properties of urethane acrylate/cycloaliphatic epoxide hybrid polymers produced by the dynamic modulation method. Raman spectroscopy was used to simultaneously monitor acrylate and epoxide functional moieties during hybrid photopolymerizations under dynamic modulation conditions. Dynamic mechanical analysis was performed to determine glass transition temperature, crosslink density, and phase behavior. In addition, film tension test was performed to understand stress-strain behavior of final hybrid polymers. Additionally, the interplay between illumination and temperature on structures and physical/mechanical properties of hybrid polymers will be intensively discussed in correlation with the kinetics of epoxide/acrylate hybrid photopolymerization.