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

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. Two series of thermoresponsive (temperature‐responsive) co‐polyacrylamides hydrogel materials to be used for smart windows were prepared using water/glycerol as a mixed solvent. By investigating the effect of co‐monomer and glycerol content on LCST and freezing point of materials, it was confirmed that various materials with various LCSTs (17.9 ∼ 38.7°C) and freezing points (6.3 ∼ −38.5°C) can be obtained. It was found that these materials have applicability to smart windows in various temperature environments.