Polyethersulfone Membranes: The Effect of Sulfonation on the Properties

Polyethersulfone (PES) was sulfonated using chlorosulfonic acid in order to improve proton conductivity. Incorporation of ‒SO3H groups into polymer main chain through sulfonation was confirmed using FTIR and 1H NMR. Ion exchange capacity of sulfonated membranes was determined via titration. Morphological studies (AFM, SEM) revealed the presence of hydrophilic proton transfer channels, which became continuous at higher degrees of sulfonation. Thermal stability was observed from thermogravimetric analysis (TGA). Storage modulus and tan δ also exhibited an increase with degree of sulfonation as determined from DMA. Conductivity measurements and fuel cell performance showed that sulfonated samples possessed higher conductivity than virgin PES.