Humidity-responsive self-healing behavior of Polyurethane-Poly(N-isopropylacrylamide) with incorporation of ureido-pyrimidinone

The development of polymeric materials combining high mechanical strength with environmentally adaptive self-healing capability represents a key objective in smart materials research, particularly for wearable biomedical applications. This study synthesized a polyurethane-based material (PUAM) incorporating poly(N-isopropylacrylamide) (PNIPAM), and varying contents of custom-synthesized ureido-pyrimidinone (UPy) units with quadruple hydrogen bonds to investigate humidity-responsive self-healing behavior. Fourier transform infrared (FTIR) spectroscopy demonstrated a progressive increase in hydrogen bonding index (HBI) with higher UPy content. Dynamic mechanical analysis (DMA) further revealed monotonic enhancements in both storage modulus and dynamic crosslinking density ( V d ). Optical microscopy observations of scratch closure under different humidity conditions and NaCl vapor environments confirmed effective humidity-responsive self-healing, with performance positively correlating with UPy concentration. Water contact angle and hygroscopicity measurements show that a high UPy content improves the moisture absorption performance of the material. The absorbed water molecules function as plasticizers to enhance polymer chain mobility and facilitate hydrogen bond reorganization, thereby improving self-healing performance. This work provides a feasible strategy for designing high-performance smart materials with tunable humidity-responsive healing properties.