Water-Soluble Squaramide-Functionalised Copolymers for Anion Recognition.

Abstract

A series of ethylene glycol-based squaramide-containing copolymers were synthesised via a post-polymerisation functionalisation strategy. Conversion of polymeric amines to squaramides was 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 H2 PO4 - , AcO- and SO4 2- over other common anions tested. The anion response and selectivity towards anions was similar to that of analogous small-molecule squaramides, however polymeric squaramides exhibited a greater resistance to deprotonation by more basic anions, which was 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 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. This article is protected by copyright. All rights reserved.