Design of Self-Cross-Linkable Poly(n‑butyl acrylate)-co-poly[N‑(hydroxymethyl)acrylamide] Amphiphilic Copolymers toward Elastic and Self-Healing Properties

A huge challenge for developing self-healing materials is achieving a good compromisation between mechanical properties and self-healing efficiency. For this purpose, a facile route by introducing N-(hydroxymethyl)­acrylamide (NMA) as a thermal-catalyzed self-cross-linker as well as a self-healing material into a soft polymer system for tuning the mechanical properties in an easy way, resulting in elastic and self-healing properties through a covalent and dynamic network simultaneously, represents an exciting avenue for the development of self-healing materials. Specifically, we propose a simple strategy to synthesize a self-cross-linkable poly­{(n-butyl acrylate)-co-[N-(hydroxymethyl)­acrylamide]} (PBA x -co-PNMA y ) amphiphilic copolymer prepared by radical polymerization method, where x and y are BA and NMA ratios, respectively, based on the monomer composition in the obtained copolymer. The mechanical properties and self-healing efficiency of the copolymer can be easily tuned by controlling the monomer ratios and varying the self-cross-linking reaction conditions. PBA0.8-co-PNMA0.2 in bulk solid state possesses a stretchability of up to 191%, maximum stress of 571 kPa, and a self-healing efficiency of 90% in ambient conditions without any interventions. Owing to the hydrophobic nature of PBA in the copolymer system, self-healing can be triggered even underwater. Furthermore, a microscale thin film bestowed with identical self-healing and mechanical properties can be fabricated and the behavior of the copolymer in thin-film form was inspected using a pseudofreestanding tensile tester machine. This work provides insight into the future design of materials with elastic, self-cross-linking, and self-healing properties, which are adjustable depending on the desired applications.