Intrinsically Flexible Phase Change Fibers for Intelligent Thermal Regulation

Owing to the significant latent heat generated at constant temperatures, phase change fibers (PCFs) have recently received much attention in the field of wearable thermal management. However, the phase change materials involved in the existing PCFs still experience a solid‐liquid transition process, severely restricting their practicality as wearable thermal management materials. Herein, we, for the first time, developed intrinsically flexible PCFs (polyethylene glycol/4,4'‐methylenebis(cyclohexyl isocyanate) fibers, PMFs) through polycondensation and wet‐spinning process, exhibiting an inherent solid‐solid phase transition property, adjustable phase transition behaviors, and outstanding knittability. The PMFs also present superior mechanical strength (28 MPa), washability (> 100 cycles), thermal cycling stability (> 2000 cycles), facile dyeability, and heat‐induced recoverability, all of which are highly significant for practical wearable applications. Additionally, the PMFs can be easily recycled by directly dissolving them in solvents for reprocessing, revealing promising applications as sustainable materials for thermal management. Most importantly, the applicability of the PMFs was demonstrated by knitting them into permeable fabrics, which exhibit considerably improved thermal management performance compared with the cotton fabric. The PMFs offer great potential for intelligent thermal regulation in smart textiles and wearable electronics.