Ionic Purity and Connectivity of Proton-Conducting Channels in Fluorous-Ionic Diblock Copolymers

Diblock copolymers of sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) [P(VDF-co-HFP)-b-SPS] were prepared for the purpose of studying the role of ionic purity and connectivity on proton exchange membranes. Block ratios were controlled to provide membranes with different morphologies. Within each membrane series, the ion content was controlled either by varying the length of the fully sulfonated polystyrene (PS) block, or by varying the degree of sulfonation of a fixed PS block. For a given ion exchange capacity (IEC), water uptake and proton conductivity were shown to be significantly influenced by the degree of sulfonation of the PS block and, thus, the ionic purity of the “ion-rich” channels. Fully sulfonated membranes with 6–17 vol % PS possessed disordered ionic clusters (6–20 nm in diameter). Although these membranes show relatively high water sorption at low IEC ranges, their water sorption and proton conductivity are less sensitive to changes in IEC. This reduced their ten...