Supramolecular polymer networks contain non-covalent crosslinks which enable access to broadly tunable mechanical properties. Previous studies have focused on materials with cross-links based on a single supramolecular interaction, or multiple in <i>series</i>, with properties dictated by the weakest link. Here we introduce the concept of a hierarchical supramolecular crosslink wherein two distinct supramolecular interactions exist. By using polymer-linked metal-organic cages both metal-ligand coordination bonding and host-guest binding can be realized in <i>parallel</i> within a single crosslink. This feature allows us to design materials with nearly identical equilibrium properties but divergent non-equilibrium and dynamic properties as host-guest binding is introduced and further modulated. We find that relaxation times proportionally increase as the strength of guest binding increases while maintaining near equivalent moduli. Additionally, we take advantage of strong guest binding behavior to stabilize the formation of metal-organic cages in the presence of super-stoichiometric metal ions or competing ligands to design systems that undergo triggered gelation or degradation in the presence of a specific guest molecule.

Hierarchacal supramolecular junctions in polymer metal-organic cage gels: selective small-molecule tunable mechanical properties and triggered sol-gel transitions

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ACS Fall 2022

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