Self‐Healing Hydrogels by Metal Complexation of 2,6‐Bis(1,2,3‐triazol‐4yl)pyridine Functionalized Tetra‐Arm Star Poly(ethylene glycol)

Abstract

AbstractThe fabrication of 2,6‐bis(1,2,3‐triazol‐4yl)pyridine (btp) based metallo‐supramolecular gels has been mainly focusing on organogels. Only recently, the synthesis and metallo‐supramolecular hydrogel formation of linear poly(ethylene glycol) (PEG) with multiple btp units in the main chain are reported. In this manuscript, metallo‐supramolecular hydrogels that are constructed using tetra‐arm star PEG‐modified with btp end‐groups upon complexation with transition metal ions are reported. This btp‐functionalized star‐PEG precursor is more easily accessible and more defined than the previously reported linear system while also yielding stronger hydrogels. The gelation is selectively induced by Ni2+ ions and strongly depended on the metal‐ligand ratio and polymer concentration. The successful formation of organogels can be induced selectively by Ni2+ or Fe2+ ion complexation in acetonitrile, which leads to the strongest complexes. The inability to form hydrogels with Fe2+ ions is ascribed to the partial oxidation of Fe2+ to Fe3+ ions in an aqueous solution. Furthermore, the optimal conditions for achieving self‐healing capabilities are also determined (i.e., 4 wt% polymer concentration and btp:Ni2+ molar ratio of 2:1) using rheology. The high strain resistance and fast self‐healing characteristics make these specific Ni2+ metallo‐supramolecular hydrogels a promising platform for materials design with potential applications in supramolecular chemistry, coordination chemistry, and catalysis.