Water‐Soluble Squaramide‐Functionalized Copolymers for Anion Recognition

Abstract

AbstractA series of ethylene glycol‐based squaramide‐containing copolymers are synthesized via a post‐polymerization functionalization strategy. Conversion of polymeric amines to squaramides is found to proceed in good yields, representing a versatile method of incorporating squaramides into polymers for anion recognition. Analysis of the polymers by UV‐Vis and fluorescence spectroscopy revealed that anion binding takes place similarly to that of small‐molecule squaramides. The presence of a fluorescent sensing group on polymer‐bound squaramides allowed for a fluorescent sensing mechanism for anions that followed a similar trend in selectivity in aqueous DMSO solution, with selectivity observed for H2PO4−, AcO− and SO42− over other common anions tested. The anion response and selectivity towards anions is similar to that of analogous small‐molecule squaramides, however polymeric squaramides exhibited a greater resistance to deprotonation by more basic anions, which is attributed to the closer proximity of individual squaramides on a macromolecule. The squaramide‐containing polymers exhibited good water solubility, overcoming a common problem for anion sensors which are typically not sufficiently soluble in water to function in many required applications. Despite no anion binding being observed in water, this study represents a simple and effective method of creating fully water‐soluble anion receptors which may be adapted to give improved binding affinity and selectivity depending on the anion binding moiety.