The transport properties of a series of sulfonated poly(phenylene)s were found to strongly correlate to the ion exchange capacity of the polymer. Sulfonated poly(phenylene) membranes have shown promise as proton exchange membranes for fuel cells. In general, these materials have minimal methanol and glucose crossover while maintaining high proton conductivity, which is necessary for efficient operation of fuel cells powered by liquid fuels. Proton conductivity in addition to methanol and glucose permeability were compared to Nafion as a function of ion exchange capacity. It was found that the transport in Nation membranes was much higher than that in the sulfonated poly(phenylene)s for a given ion exchange capacity. Water content and its absorbed state within membranes were elucidated by differential scanning calorimetry in order to provide insight as to how the transport properties varied between the materials studied. The domain morphology of these ionomers was imaged with transmission electron microscopy in order to contrast the morphological differences between Nafion and the sulfonated poly(phenylene) series. (c) 2006 Published by Elsevier Ltd.