Healable and self-healing polyurethanes using dynamic chemistry

Ever since the emergence of polymers, there has been interest in the production of "self-healing" materials. Over the last decade this dream has become closer to reality with the development of polymer networks containing dynamic bonds that are capable of recovering their physical properties following damage. In this review article, we provide a comprehensive summary of the work relating specifically to polyurethane materials, which constitute one of the most promising classes of polymers to be used in self-healing applications. After a brief introduction to the fundamental concepts behind healing in generic dynamic bond-containing polymer systems, the rheological characteristics necessary to heal cuts and scratches, and the rheological properties that make polyurethanes particularly interesting are described. Subsequently, we detail the range of dynamic bonds that can be incorporated into polyurethanes and how the nature of the dynamic bond influences the rheological properties of polyurethanes. Following this, we provide an overview of the characterization techniques that may be applied to measure the extent of healing. Finally, we discuss the commercial applications of such healable polyurethanes, highlighting the factors that stand in the way of their widespread use. (c) 2021 Elsevier B.V. All rights reserved.