Sulfonation and Characterization of Poly-(styrene-isobutylene-styrene) Proton Exchange Membranes

This study sulfonated several tri-block copolymers composed of poly-(styrene-isobutylene-styrene) (SIBS) to create ionomers used as proton exchange membranes (PEMs). Linear and branched SIBS were sulfonated to high ion exchange capacities (IEC) (e.g., 90% sulfonation of available polystyrene). The membranes were characterized using thermogravimetric analysis (TGA), water swelling and differential scanning calorimetry (DSC). The characterization of these membranes reveals that they can maintain the IEC and thermogravimetric properties, while reducing the methanol permeability by one order of magnitude. These results can be significant to overcome the methanol cross-over problem in direct methanol fuel cells (DMFC).