Engineering HydrophobicHierarchical SupramolecularInteractions in Reversibly Cross-Linked Elastomers for OutstandingWater Resistance

Achieving outstanding water resistance in reversibly cross-linked elastomers (RCEs) remains challenging due to the presence of polar and hydrophilic groups within polymer chains. In this study, we present the fabrication of mechanically robust, healable, and recyclable RCEs with exceptional water resistance by incorporating hydrophobic hierarchical supramolecular interactions into poly(tetramethylene ether glycol) (PTMEG)-based polyurethane elastomers. These hierarchical supramolecular interactions, consisting of hydrogen bonding and π-π stacking, exhibit high binding energy, facilitating the in situ formation of phase-separated hydrophobic nanostructures that significantly enhance the water resistance of the elastomers. Consequently, the elastomers exhibit outstanding water resistance, with a water absorption as low as 1.1 wt % even after 40 days of immersion in water. In addition to their superior water resistance, the elastomers exhibit excellent mechanical properties, including a tensile strength of ∼67.8 MPa, toughness of ∼633 MJ m^–3, and fracture energy of ∼160 kJ m^–2. These mechanical properties are attributed to the synergistic effects of phase-separated nanostructures and strain-induced crystallization of PTMEG segments. Furthermore, the reversibility of the hydrophobic hierarchical supramolecular interactions enables the convenient healing and recycling of the elastomers, allowing the healed and recycled elastomers to restore their original mechanical performance. These elastomers were further demonstrated to be effective in encapsulating flexible electrochromic devices for underwater applications.