The effects of water binding and morphology will be reported in the context of designing new proton exchange membranes (PEMs). While much has been learned about the function of proton exchange membranes by studying perfluorosulfonic acid and sulfonated aromatic polymers, new generations of proton-conducting polymers for aqueous applications are being developed. Key to these advancements have been block copolymers and random copolymers with new sulfonic-acid bearing headgroups.

Sulfonated aromatic block copolymers are a known route to high-performing proton exchange membranes. Compared to their random sulfonated copolymer counterparts, the organization of the sulfonate groups in a concentrated ionic domain has demonstrable benefits to proton conductivity. However, the relative humidity effects on the specific headgroup chemistry still often lead to lower conductivity than desirable at low RH.

Using FTIR, we have explored the water binding in aromatic random copolymers with a number of new sulfonate groups. Our data shows that superacid groups on aromatic backbones can give comparable conductivities to perfluorosulfonic acid membranes. The interaction of these headgroups with water is one of the important factors for high proton conductivity – even though their morphologies can be much different than block copolymers or perfluorosulfonic acid materials.

This talk will discuss the morphology and water binding factors that influence the proton conductivity of a number of unique aromatic polymer-based proton exchange membranes.