Construction of a Dynamic Ultrastretchable Epoxy Network\nBased on Chemical–Physical Cross-Linking Transformation

Conventional epoxy resins have high\ncross-linking density and rigid\nmolecular structures, which make them difficult to develop into flexible\nelastomers. Here, inspired by the cuticle of the marine mussel byssi,\nwe incorporate reversible Fe<sup>3+</sup>–carboxyl cross-links\ninto a cross-linked epoxy network through a transformation between\nchemical cross-links and physical cross-links to realize the construction\nof a dynamic cross-linked network in traditional epoxy resins. Dynamic\ncross-linking networks and long flexible chain segments endow the\nepoxy system with excellent stretchable properties. Carbon nanotubes\ncoated with ferric oxide (Fe<sub>3</sub>O<sub>4</sub>) nanoparticles\nwere synthesized and added to the epoxy system, reinforcing the epoxy\nsystem. The synergistic combination of the modified molecular structure\nand nanohybrid endows the epoxy system with 550% elongation at break,\na tensile strength of 1.4 MPa, and the ability to respond quickly\nto an applied magnetic field. An ultrasensitive strain sensor was\nconstructed from synthetic epoxy hybrid materials; the GF (strain\ncoefficient) of the strain sensor was up to 344.32. This research\nwill be beneficial in expanding the application range of traditional\nepoxy polymer materials in the emerging sensor field.