Oxygen-Tolerant Fabrication of Large-Area Hydrogel Films via Photoinduced Electron/Energy Transfer-Reversible Addition-Fragmentation Chain Transfer Polymerization

Hydrogel thin films are promising form factors for biomedical applications, wearable electronics, and energy technologies owing to their biocompatibility, skin conformality, and tunable physiochemical properties. Covalently cross-linked hydrogels and their films are typically prepared via the free-radical polymerization of vinyl monomers, which requires additional time and apparatus to remove oxygen and retain oxygen-free conditions. In this study, an oxygen-tolerant photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to prepare hydrogels from an aqueous pregel solution containing an acrylamide-based monomer, a polymeric cross-linker, a RAFT agent, a photoredox catalyst, and an electron donor under moderate green-light irradiation. The formation of the cross-linked network was further optimized by varying the chemical composition and light intensity. Using the developed hydrogel preparation, a large-area hydrogel film was fabricated under open-air conditions for application in the development of an energy-saving solar control device, and its switching temperature was further controlled via a random copolymerization of temperature-responsive polymers.