Nested Non-covalent Interactions Expand the Functions of Supramolecular Polymer Networks

Abstract

Supramolecular polymer networks contain reversible crosslinks that enable access to broadly tunable mechanical properties and stimuli-responsive behaviors. The incorporation of multiple unique supramolecular interactions within such materials can further expand their mechanical responses and functionality. To date, however, the design of supramolecular networks leveraging multiple distinct interactions has been accomplished through discrete combinations of independent supramolecular interactions, limiting materials design logic. Here we introduce the concept of leveraging “nested” supramolecular crosslinks, wherein two distinct supramolecular interactions exist in parallel and influence each other, to control bulk material functions. We demonstrate this concept using polymer-linked Pd2L4 metal-organic cage gels (polyMOCs) that exhibit both metal–ligand coordination and host-guest binding interactions within a single metal-organic cage network junction. The interplay of guest binding thermodynamics and metal–ligand exchange within each junction enables modulation of gel dynamics independent of stiffness, expands the stoichiometric window for gel assembly, and enables reversible sol-gel transitions as guest binding is introduced and further modulated. Such properties are not obtainable in traditional supramolecular materials where metal–ligand coordination and host-guest binding interactions exist in series.