Tough self-healing elastomers by molecular enforced integration of covalent and reversible networks

TL;DR

This paper introduces a novel hybrid polymer network that combines covalent and reversible bonds at the molecular level, resulting in tough, self-healing elastomers with high fracture energy and room-temperature healing capabilities.

Contribution

The authors develop a new method to integrate covalent and reversible bonds in dry elastomers without co-solvents, enhancing toughness and self-healing performance.

Findings

Fracture energy of 13,500 J/m^2 comparable to natural rubber

Self-heals at room temperature with 4 MPa tensile strength

Molecular-level mixing of bonds improves mechanical properties

Abstract

Self-healing polymers crosslinked by solely reversible bonds are intrinsically weaker than common covalently crosslinked networks. Introducing covalent crosslinks into a reversible network would improve mechanical strength. It is challenging, however, to apply this design concept to dry elastomers, largely because reversible crosslinks such as hydrogen bonds are often polar motifs, whereas covalent crosslinks are non-polar motifs, and these two types of bonds are intrinsically immiscible without co-solvents. Here we design and fabricate a hybrid polymer network by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks. The randomly branched polymer links such two types of bonds and forces them to mix on the molecular level without co-solvents. This allows us to create a hybrid dry elastomer that is very tough with a fracture energy $13,500J/m^2$ comparable to that of natural rubber; moreover, the elastomer can self-heal at room temperature with a recovered tensile strength 4 MPa similar to that of existing self-healing elastomers. The concept of forcing covalent and reversible bonds to mix at molecular scale to create a homogenous network is quite general and should enable development of tough, self-healing polymers of practical usage.