Polymers healed autonomously and with the assistance of ubiquitous stimuli: how can we combine mechanical strength and a healing ability in polymers?

Abstract

Among various approaches to create self-healing polymers, the introduction of dynamic bonds to polymers is one of the most powerful approaches. Macroscopic failure of such polymers is usually accompanied by the cleavage of dynamic bonds at the broken surfaces, which can then reform due to their reversible nature and repair the failure. However, since the reformation of dynamic bonds requires molecular mobility, autonomous healing at room temperature is almost completely limited to polymers with good molecular mobility, such as gels and soft elastomers. Mechanical strength usually conflicts with a high molecular mobility, as well as an autonomous healing ability. In this review, we first overview recent successful approaches to overcome this limitation. These approaches include combining careful dynamic bond chemistry choices and smart designs of the environment around the dynamic bonds. In the latter part of this review, attempts to design mechanically robust polymers that can heal with the assistance of ubiquitous stimuli are summarized. Such a healing process is a suboptimal choice for practical, valuable healing materials.