Self-healing polyurethane elastomers: An essential review and prospects for future research

Drawing inspiration from nature, such as the self-healing ability of skin injuries, researchers are increasingly exploring the use of self-healing polyurethane elastomers to design safer, longer-lasting, and better-performing materials. In this paper, we have reviewed the progress in the study of self-healing polyurethane elastomeric materials based on the self-healing mechanism from two classes, intrinsic self-healing polyurethane elastomers and external self-healing polyurethane elastomers. The intrinsic self-healing polyurethane elastomers can be classified into three categories based on the type of self-healing bonds: self-healing polyurethane elastomers with reversible non-covalent bonding, self-healing polyurethane elastomers with reversible covalent bonding, and self-healing polyurethane elastomers with multiple bonds. Self-healing polyurethane elastomers with reversible non-covalent bonds are constructed from hydrogen bonds, π–π stacking, ionic interactions, and coordination bonds. Self-healing polyurethane elastomers with reversible covalent bonds were constructed by disulfide bonds, Diels-Alder dynamic covalent bonds, acylhydrazone bonds, and borate ester bonds. In addition, there have been proposals for self-healing polyurethane elastomers that exhibit improved properties by combining reversible non-covalent and reversible covalent bonds in various bonding configurations. Self-healing polyurethane elastomers with external support have primarily been introduced as microencapsulated self-healing polyurethane elastomers. The paper summarizes the self-healing properties, the elongation at break, tensile strength, and self-healing mechanism of self-healing polyurethane elastomers as studied by previous researchers. Finally, the application of self-healing polyurethane elastomers is briefly described. Additionally, the development directions and application prospects of high-strength self-healing polyurethane elastomers are discussed. It is expected that this paper will provide guidance and serve as a reference for researchers who are interested in preparing self-healing polyurethane elastomers.