Kinetic study of photoinduced quasi-simultaneous interpenetrating polymer networks

Interpenetrating Polymer Networks (IPNs) based on a dimethacrylate and an epoxide are synthesized by photopolymerization. By varying the relative amount of radical photoinitiator with respect to the cationic one, and by changing the exposure conditions, it was found possible to delay or accelerate the photopolymerization of the methacrylate monomer compared to the epoxide one. The effect of the relative rate of photopolymerization on the final conversion, glass transition, and morphology is discussed. Finally, the increase in shear modulus as a function of irradiation time was investigated by real time ultrasonic reflectometry. An increase in the mechanical properties after the exposure was evidenced as a consequence of the living character of the cationic polymerization.

Graphical abstractThe kinetics of IPN formation between a cycloaliphatic epoxide and a methacrylate can be controlled by modifying the radical photoinitiator concentration and the nature of the light source. The change in the sequence order results in different final properties. The systems where epoxide polymerizes first lead to brittle materials with the presence of extractables. By contrast, homogeneous and highly crosslinked materials are obtained for the systems where methacrylate cures first. Moreover, real time ultrasonic reflectometry has evidenced that their shear modulus keeps increasing even 7 h after the IPN photogenesis due to the living character of the epoxide polymerization.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Quasi-simultaneous IPN can be formed using methacrylates and epoxides. ► The sequence of kinetics in the photopolymerization governs the final mechanical properties. ► Real-time ultrasound reflectometry shows the growth of mechanical properties during irradiation and after curing.