Mild-Temperature Self-Healing Bio-Based Polyurethane Film Enabled by Dual Dynamic Covalent Bonds and Segmental Design

Abstract

This study successfully developed a bio-based polyurethane (PU-S-D) film that combines high mechanical strength with excellent mild-temperature self-healing properties. The material was prepared by pre-polymerizing castor oil with isophorone diisocyanate (IPDI), followed by chain extension using a mixture of 2-hydroxyethyl disulfide (HED) and dimethylglyoxime (DMG) as mixed chain extenders, constructing a multi-dynamic synergistic network wherein weaker disulfide bonds afford mild-temperature self-healing, stronger oxime-urethane bonds provide robust mechanical strength, and multiple hydrogen bonds serve to reinforce and integrate these functionalities. The structure and properties of the bio-based polyurethane film were thoroughly analyzed and discussed. This bio-based polyurethane film exhibits a high gel fraction (~90%) after more than 72 h and relatively high thermal stability (T₅₀% > 400℃). The glass transition temperature (Tg) of the film material is controlled near 30℃, ensuring it possesses sufficient molecular chains mobility at mild-temperature to trigger self-healing while simultaneously maintaining excellent mechanical strength. The mechanical performance results of film are outstanding: compared to the pure PU film, the tensile strength of the PU-S-D film increased by approximately 862% (reaching 12.4 MPa), while the elongation at break exceeded 310%. The film demonstrates remarkable self-healing performance, achieving a repair efficiency of 83% under conditions of 35℃ for 12 h. Molecular dynamics simulations and in situ infrared spectroscopy indicated that the dynamic disulfide bonds spontaneously recombine after fracture and induce the film's repair process. This research provides a method for developing bio-based, low-cost, high-performance materials. The developed dynamic covalent polyurethane network holds significant potential for practical applications requiring long-term durability and high reparability, such as protective coatings, high-performance adhesives, and durable composite matrices.