Hierarchical Energy-Dissipating Networks: An Interaction-Level Design Principle for Tough, Stable, and Sustainable...

Elastomeric materials are used where few other polymeric materials can operate: in components that must deform repeatedly, recover rapidly, and continue to bear load under mechanical or environmental stress. Yet the molecular features that give elastomeric materials high performance often work against sustainability. The same interactions that make an elastomeric material reliable in service often make it difficult to heal or recycle. Weakening the network improves mobility but usually undermines the mechanical integrity that elastomeric materials are expected to provide. Early studies on supramolecular elastomers demonstrated that reversible hydrogen bonding, ionic association, metal-ligand coordination, and other noncovalent motifs could impart thermoreversibility, self-healing capability, and stress relaxation behavior to materials. Covalent-supramolecular networks combine stable covalent backbones with reversible physical associations, allowing mechanical integrity and local molecular mobility to be regulated at different structural levels. Dynamic covalent networks, including vitrimers and other covalent adaptable networks, introduce exchangeable covalent bonds that enable topology rearrangement, reshaping, repair, and reprocessing while maintaining network connectivity. The central design problem is therefore to make network dynamics conditional: active enough to dissipate energy and enable reconstruction, but restrained enough to preserve integrity during service. Our recent work addresses this question through hierarchical energy-dissipating networks (HEDNs). In HEDNs, supramolecular interactions and covalent linkages are not simply combined; they are assigned different mechanical roles and activated at different stages of deformation or processing. Under deformation, weaker interactions dissociate first to dissipate energy, while stronger interactions and covalent frameworks preserve network integrity. During healing, reprocessing, or upcycling, reversible interactions provide the mobility and adaptability needed for network reconstruction and component integration. Thus, hierarchical energy dissipation serves not only as a toughening mechanism, but also as a molecular strategy for coordinating mechanical robustness, structural stability, and sustainable reuse. This Account highlights three roles of this strategy in our studies of supramolecular elastomers and ionogels. In thermoplastic elastomers, staged supramolecular dissociation allows stress to be dissipated without destroying the load-bearing framework, leading to exceptional strength and toughness. In chemically cross-linked elastomers, covalent frameworks and reversible motifs divide the roles of stability and reconfiguration, enabling thermoset-like robustness together with thermal healing and reprocessing. In postservice materials, preinstalled interaction sites further allow discarded elastomers or ionogels to accommodate ionic liquids, carbon nanotubes, and other functional components, turning recycling into functional upcycling. Together, these studies establish HEDNs as a design principle for elastomeric materials that are tough, stable, reprocessable, and upcyclable.