Reversible interpenetration enables mechanical robust, self-healable and recyclable double covalent adaptable network elastomers

Achieving both high performance and recyclability in thermoset elastomers is of critical importance for energy sustainability. Double network (DN) polymers exhibit excellent mechanical properties but often struggle to balance recyclability and mechanical robustness due to their reliance on permanent or weak bonds. Here, we propose the concept of a nanostructured interpenetrating double dynamic network (DDN) by introducing dynamic covalent bonds (DCBs) into two distinct networks. Compared to single dynamic networks (SDNs), DDNs display a higher topological freezing transition temperature and a lower glass transition temperature. These effects are attributed to the restricted bond exchange due to network interpenetration and enhanced dynamic heterogeneity, respectively. At low bond swap energy barriers (ΔΕ_sw), DDNs exhibit superior stress-strain behavior and toughness over SDN, demonstrating a synergistic “one plus one is greater than two” effect. This enhancement arises from coordinated orientation and topological regulation that alleviates stress concentration. High ΔΕ_sw induces stress concentration, bond breakage, and diminished network orientation, leading to a “one plus one is less than two” effect. Optimal mechanical performance is achieved when the two networks in DDN with moderate cross-link density disparity (δ_ρ). In such case, the stiffer network sustains the external force at small strains to maintain the integrity of the softer network, which then contributes at larger strains. Further, the introduction of DCBs enables excellent self-healing capability of DDN. Finally, we show that DDNs exhibit controllable interpenetration and de-interpenetration. When the interaction between the two networks (ε_inter) in DDN is weaker than the interaction within the respective network (ε_intra), phase separation and eventual de-interpenetration occur at low ΔΕ_sw. But when ε_inter≥ε_intra, low ΔΕ_sw accelerates the re-interpenetration of phase separated networks, enabling efficient closed-loop recyclability. This study provides a theoretical foundation for the design of high-performance, self-healing, and sustainable polymer materials.