Preparation and characterization of thermoresponsive poly(N‐isopropylacrylamide‐co‐N‐isopropylmethacrylamide) hydrogel materials for smart windows

Abstract In this study, a series of thermoresponsive cross‐linked copolymer poly [N‐isopropylacrylamide(NIPAm)‐co‐N‐isopropylmethacrylamide(NIPMAm)] (P‐M series samples: P‐M‐0, 10, 20, 30, 40, where numbers are co‐monomer contents) hydrogels were prepared by free radical polymerization using the main monomer N‐isopropylacrylamide (NIPAm), co‐monomer N‐isopropylmethacrylamide (NIPMAm), cross‐linking agent N, N‐methylenebisacrylamide, initiator (ammonium persulfate)/catalyst, and solvent water. In addition, a series of samples [P‐G series samples: P‐G‐0, 10, 20, 30, 40, where numbers are co‐solvent glycerol content) were prepared using P‐M‐40 as components and water/co‐solvent glycerol as a mixed solvent. The effects of co‐monomer NIPMAm and co‐solvent glycerol contents on the lower critical solution temperature (LCST)/freezing temperature and light transmittance as function of temperature of the prepared copolymer gels were investigated. The resulting thermoresponsive polymer gels had LCSTs in the range of 17.9 to 38.7°C and freezing points in the range of 6.3 to −38.5°C. These gels are suitable materials for smart windows that are responsive to various environmental conditions.