Structure and Water Characteristics of N-isopropylacrylamide-based Polymer/Polyurethane Resin Films

Context: Moisture-permeable waterproof materials are used in fields such as sports to provide comfort. In this study, we investigated moisture-permeable waterproof film materials exhibiting temperature-sensitive hydrophilicity for application in agriculture, industry, and sports. Objective: By combining water-soluble poly(N-isopropylacrylamide) (poly-NIPAM) with hydrophilic polyurethane (PU), we investigated whether the resultant copolymer films can be used as moisture-permeable waterproof materials with good potential applications. Methods: We copolymerized water-soluble poly-NIPAM, which was synthesized beforehand as a diol, with PU, and studied whether the resulting poly-NIPAM/PU copolymer films were water-insoluble. Results: We confirmed that water-soluble poly-NIPAM and hydrophilic PU were combined through PU links. In terms of physical properties, we verified that the films had indeed become water-insoluble. Furthermore, from the relationship between the film’s water swelling ratio and water temperature, we observed that the film exhibited temperature-sensitive hydrophilicity, with the water swelling ratio changing across the LCST. For films absorbing water at different temperatures, the drying rate was different across the LCST. Conclusions: From these results, we confirmed that a functional film with temperature-dependent hydrophilicity was achieved. This property enabled the poly-NIPAM/PU copolymerized films to be used as moisture-permeable waterproof fabrics for sportswear.