Methacrylate-Epoxy\nPhotopolymer Networks via Orthogonal\nFree-Radical/Epoxy-Acid Reactions in Neat Conditions

We report a series of photopolymer\nnetworks fabricated by free-radical\npolymerizations of methacrylic acid (MAA) followed by epoxy-acid reactions.\nThe free-radical polymerization was accelerated by hydrogen bonding\nbetween MAA and multifunctional epoxide. The subsequent epoxy-acid\nreaction eliminated free acids, resulting in hydrophobic, covalently\ncross-linked network polymers. These hybrid MAA-epoxy resins showed\nlow viscosities (<36 cP @ 23 °C) while maintaining fast reaction\nkinetics. Using 405 nm UV light (5 mW/cm<sup>2</sup>), 50% MAA conversion\nwas achieved within 13 s; quantitative conversion was within 2 min.\nMacroscopic phase separation was observed after the MAA polymerization,\nwhich was mitigated by the addition of other monofunctional methacrylate\nmonomers as “reactive diluents.” When the reactive diluents\nwere included, we obtained glassy materials with robust mechanical\nproperties, including <i>T</i><sub>g</sub> values ranging\nfrom 81 to 136 °C and Young’s modulus ranging from 860\nto 1410 MPa. These hybrid MAA-epoxy resins enable a platform for the\ndesign of photopolymers beyond the typical multifunctional polyester-based\nmethacrylate oligomers.