Multistimuli, Multiresponsive Fully Supramolecular Orthogonally Bound Polymer Networks

Their dynamic and stimuli-responsive nature makes supramolecular bonds useful for the design of functional polymers with adaptable properties. The combination of multiple types of supramolecular interactions in one material permits, in principle, access to multistimuli, multiresponsive polymers, but examples of solid materials in which different supramolecular interactions have led to useful orthogonal responses toward different stimuli are rare. Here we report a new materials platform that involves two orthogonally bound supramolecular networks. The network components are based on a trifunctional poly(propylene oxide) that was terminated with either 2,6-bis(1'-methylbenzimidazolyl)pyridine (Mebip) ligands or 2-ureido-4[1H]pyrimidinone (UPy) groups. Supramolecular cross-linking was achieved by complexing the Mebip motifs to Zn2+ ions and UPy dimerization via hydrogen bonding, respectively. Orthogonal binding of the metalligand complex and the hydrogen-bonding motifs was confirmed via spectroscopically monitored titrations. Dynamic mechanical analyses and small-angle X-ray scattering data reveal that the properties of the supramolecular networks are governed by the microphase segregation of the binding motifs into two well-defined hard phases. The ability to independently disassemble the metalligand complexes and UPy dimers by chemical and thermal stimuli was exploited to access double and triple shape-memory and selective healing behaviors.