Research Progress of Self-Healing Polyurethanes

Polyurethane (PU) represents a class of polymeric materials characterized by the presence of carbamate groups (―NHCOO―) within their molecular structures. Due to their superior mechanical properties and biocompatibilities, PUs are among the most promising polymer materials. PUs manifest in diverse forms, including flexible or rigid foams, chemical-resistant coatings, specialty adhesives and sealants, and elastomers. Predominantly thermoset, most PUs cannot be remelted and reshaped, and their service life is often curtailed by damage incurred during use, leading to significant environmental concerns. Introducing self-healing capabilities to enhance PU durability is an effective strategy to mitigate these issues. Self-healing methods for PUs are categorized into extrinsic and intrinsic approaches. The extrinsic approach involves incorporating microcapsules or microvessels containing repair agents or initiators into the polymer matrix to facilitate repair. Conversely, the intrinsic approach leverages the recombination of dynamic bonds within the network to achieve self-repair, including dynamic covalent bonds (e.g., disulfide bonds, Diels-Alder bonds, imine bonds) and non-dynamic covalent interactions (e.g., hydrogen bonds, coordination bonds). With advancements in dynamic bonding, research on self-healing PUs is rapidly progressing. We review the recent advancements in self-healing PUs based on dynamic covalent bonds, elucidate the impact of dynamic covalent bond exchange mechanisms on the rheological properties of PUs, and discuss the challenges and future prospects for the practical application of these innovative materials.