Intrinsic photothermal performance and flexibility of polyurethane phase change materials via π-π conjugation for personal thermal management in outdoor cold environments

Phase change materials (PCMs) with photothermal properties can effectively convert solar energy into thermal energy and store it via phase change, subsequently provide heat for human body in cold environments. The introduction of photothermal fillers into polyurethane PCMs to develop photothermal polyurethane PCMs has been widely studied. However, the incompatibility between photothermal fillers and matrix leads to severe deterioration in the composite's flexibility. Therefore, achieving both the mechanical and photothermal properties of polyurethane PCM in wearable products is a pressing issue. In this work, a polyurethane PCM with intrinsic flexibility and photothermal properties was designed. It consists of small molecules filled with π-π conjugated structures and polyethylene glycol crosslinked through chemical interactions. By selecting diamine crosslinkers with varying conjugation strengths, the influence of π-π conjugation on flexibility and photothermal properties of polyurethane PCM was investigated. The results demonstrate that the stronger the π-π conjugation, the better the photothermal performance, with a photothermal conversion efficiency reaching up to 71.4%. Additionally, the strong intermolecular forces generated by π-π stacking also endow polyurethane PCM with high-temperature morphological stability, high tensile strength (22.4 MPa), and excellent toughness (351.1 MJ/m 3 ). The intrinsic photothermal properties and good mechanical performance of polyurethane PCM make it suitable as a material for fabrics and coatings, ideal for wearable products in extreme cold environments, such as north pole and snowfields, where thermal energy is required.