UV-Curable Silane-Modified Polyurethane Acrylate with High Stretch Ability and Sensitivity for Flexible Sensors

In recent years, flexible strain sensors fabricated by using ultraviolet light-curing technologies have garnered significant attention for wearable devices and human motion monitoring. However, developing hydrophobic flexible sensors with good mechanical strength and environmental stability remains a great challenge. Herein, an ultraviolet-curable silane side-chain-modified polyurethane acrylate material was fabricated for flexible sensing applications. A hydroxyl-terminated silane coupling agent (APIP) was synthesized to modify polyurethane acrylate (PUA). The results indicate that the amount and structure of APIP affect the polymerization performance, thermodynamic properties, tensile properties, and hydrophobicity of PUA. When 20 wt % APIP was added, the sample (PUA-APIP/20%) exhibited a water contact angle of 104°, which represents a significant increase from the 74° of the original PUA. The tensile strength and elongation at break of PUA-APIP/20% increased to 8.67 MPa and 378.84%, respectively. The composite of PUA-APIP and lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) could be instantly cured under UV irradiation to produce a flexible thin-film strain sensor. This composite strain sensor was used to detect large-amplitude human movements (such as finger, elbow, and knee flexion) as well as subtle muscle contractions and can yield stable strain responses. This work offers strategies for the development and sustainable production of wearable, flexible electronic devices.