Self-healing supramolecular polymers

The ability of natural or artificial systems to heal spontaneously after damage, while retaining their functions, is an important feature of their sustainability. Self-healing is very common in biological systems. Examples include the healing of injured skin and the repair of DNA, as confirmed by the work of T. Lindahl, winner of the 2015 Nobel Prize in Chemistry. Inspired by this, self-healing systems have been widely explored over the past 15 years. Following degradation (thermal, mechanical, chemical, etc.), these materials spontaneously, or under the effect of an external stimulus, trigger a physicochemical process of self-repair to restore their initial properties. This process helps to extend their lifespan.

One of the first synthetic models of these materials was proposed by White et al . in 2001 using composite polymer materials incorporating a catalyst and capsules containing a repair agent. The disadvantage of this method is that the same region of the material can no longer be repaired once the active agent capsule has been consumed. Although improvements have been proposed, these materials are based on relatively complex systems. What's more, repair also modifies their mechanical properties, which limits their field of application.

There is also growing interest in a second family of self-repairing materials. via reversible cross-linking. In theory, the latter offer the advantage of being able to be fractured and repaired as many times as possible. This family can be divided into two groups, depending on whether their reversible cross-linking is achieved by covalent or non-covalent bonding. In this article, we will focus solely on the self-repair of polymers by non-covalent bonds, also known as supramolecular bonds.

In the first part of the article, the background to the polymer industry is presented, together with the concept of self-repairing supramolecular polymers. The next two parts deal with the development of self-repairing supramolecular polymers obtained from two different non-covalent bonds: hydrogen bonds and π-π interactions. Each of these two parts begins with the study of a basic polymer designed from one of these non-covalent bonds. It then describes the evolution of its structure in order to improve its mechanical properties, while analyzing its ability to self-repair. The final section looks at self-repairing host-guest systems using crown ether and cyclodextrin as the host molecule.