Hierarchical H-bonding and metal coordination bonds enabled supramolecular dual networks for high-performance energy-dissipation

Natural organisms have superior material properties such as mechanical adaptability, impact protection, and self-healing to protect the body from complicated external environments, fascinating the development of functional supramolecular elastic materials with biomimetic protective features. Herein, a dual physically crosslinked supramolecular polyurethane (PU) network with strain-hardening effect is synthesized by incorporating hierarchical hydrogen bonds (H-bond) and metal coordination bonds into an elastomer matrix. A moderate content of quadruple H-bonds is critical for achieving a prominent toughness and a considerable strain-at-break owing to the strain hardening effect enabled by the hierarchical H-bonds. When the Zn-to-pyridine coordination bonds were introduced to the supramolecular PU, the strength, toughness, and energy dissipation properties were further enhanced attributing to the dual physical crosslinking networks. The dynamic dissociation and association of the sacrificial H-bonds and Zn-to-pyridine coordination bonds induced significant strain hardening effect and enabled tremendous energy absorption and self-healing properties. Besides, the supramolecular PU elastomers and their blends were foamed via scCO2 foaming to produce supramolecular foams containing dynamic bonds. The composite foam could effectively reduce the impact force from 6085N to 373 N and achieve an outstanding energy absorption efficiency of 93.87 % owing to the synergistic effect of porous structure and dual physically crosslinked networks. This work provides an innovative strategy for designing high-performance energy absorbing supramolecular elastomers and cushioning foams with reversible bonds.