Statistical and Block Copolymers for Anion-Exchange Membranes with High Local Concentrations of Quaternary Ammonium Groups
We have recently developed synthetic strategies where single phenylene rings in aromatic polymers can be directly functionalized with precisely two, three, or four QA groups, allowing an excellent and systematic control over the local density and distribution of ionic groups along the polymer backbone. We have used this approach to prepare several series of statistical and multiblock copolysulfones with very high local QA concentrations to promote membrane properties. Small angle X-ray scattering of AEMs based statistical copolymers containing phenylene rings functionalized with two, three and four QA groups, respectively, showed clear ionomer peaks to indicate efficient ionic clustering. The clustering was promoted by an increasing density of QA on the single phenylene rings. Corresponding randomly functionalized copolymer membranes showed no ionomer peaks. At moderate ion-exchange capacities, the Br- conductivity of the densely functionalized copolymers was higher than that of randomly functionalized copolymers, despite a significantly higher water uptake of the latter. In the current presentation, we will discuss selected results on the synthesis and structure-property relationships of the copolymers and AEMs.
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