Self‐Healing of Polymers via Supramolecular Chemistry

Abstract

rearrangements. While one challenge is to incorporate chemical modifications enabling chemical bond reformations, equally important is the coordination of chemical events with polymer network physical changes within interfacial regions resulting from mechanical damage.Recent studies suggested that two types of dynamic bonds are highly attractive to achieve self-healing in polymers: reversible covalent bonds and supramolecular chemistry. Reversible covalent bonds offer higher bonding energies, allowing the material to regain physical properties similar to conventional polymers prior to damage. Advantages and disadvantages of reversible covalent bonding were summarized in several review articles. [5] Self-healing involving dynamic dissociation/association using supramolecular chemistry offers fast reversibility under ambient conditions reaching exceptionally quickly equilibrium state, bonding directionality, and remarkable sensitivity. Since broad-range of network structures can be obtained via supramolecular interactions, applications in soft electronics, sensing, biomedical technologies, 3-4D printing, and reprocessable materials are highly attractive and may open many new technological opportunities (Figure 1). Mechanical integrity using supramolecular chemistry is achieved by the formation of multiple noncovalent interactions between multiple associative groups covalently attached to polymer side chain or chain ends of macromolecular building blocks. These interactions include H-bonding, metal-ligand complexation, hostguest, ionic interactions, π-π stacking, and hydrophobic interactions. They are depicted in Figure 1. In contrast to covalent rebonding, mechanical properties of supramolecular polymer networks are achieved by the presence of these secondary interactions forming noncovalent crosslinks, which bind liquid-like building blocks into plastic or rubbery polymers in hydrated and nonhydrated states. The dynamic nature of these noncovalent bonds provides an opportunity for self-healing attributed to reassociation of supramolecular components, similar to secondary interactions found in living systems that regulate many living functions. The rule of thumb in designing these networks is that the degree of association is determined by the equilibrium constant (K a ) values, whereas dynamics is driven by rate constants of the association-dissociation reactions, k a and k d , respectively. [6] Molecular structural and electronic features along with network heterogeneities are of particular importance in these networks. Mechanical strength and elasticity of supramolecular polymers are determined by not only the K a values, but also stacking and clustering of the associative groups which may result in heterogeneities leading to the Recent advances of supramolecular chemistry utilized in the development of self-healing polymers have revealed that the rate and equilibrium constants of bond dissociation/re-association, bonding directionality, chain relaxation time, decay rate of chain relaxation after damage, and clu...

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“…In this section, we summarize recent research progresses in the self‐healing function of different surface damage forms, such as cracks, scratches, punctures, and surface wear. In the past several years, there are some studies that are reported on self‐healing surface damages involving different materials, such as metal, ceramics, and polymers . In the following paragraphs, we will mainly concentrate on some relatively new progresses in self‐healing surface damages, and emphasize the intermolecular bonds formation and molecular chain mobility at damaged material interface.…”

“…as metal, ceramics, and polymers. [53][54][55] In the following paragraphs, we will mainly concentrate on some relatively new progresses in self-healing surface damages, and emphasize the intermolecular bonds formation and molecular chain mobility at damaged material interface.…”

Self‐Healing Materials are Coming of Age

“…Collage of self‐healing materials addressed in the current Special Issue. Reproduced with permission …”