High methanol crossover through the currently used Nafion^® membranes from the anode to the cathode is a critical issue in direct methanol fuel cells since it not only wastes the methanol fuel but also poisons the cathode Pt catalyst.^[1] In this regard, aromatic hydrocarbon-based polymer membranes have been suggested as alternatives in past decade.^[2] However, most of the sulfonated membranes, in which the sulfonic acid moieties are incorporated directly onto the backbones, generally suffer from high water swelling and poor hydrolytic stability when increasing the degree of sulfonation.^[3] To improve the osmotic and hydrolytic stabilities of the sulfonated polymers, it is desirable to increase the hydrophilic-hydrophobic separation by locating the sulfonic acid groups away from the polymer main chains.^[3] Perfluorocyclobutyl aryl ether polymers, combining the engineering thermoplastic nature of poly(aryl ether)s and the stability of fluorocarbon segments, exhibit high thermal/oxidative/mechanical stability, good chemical resistance and flexibility, and low moisture absorption.^[4] In this work, novel perfluorocyclobutyl aryl ether polymers with flexible pendant sulfonic acid groups were prepared  by grafting and characterized by nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. The thermal characterization data show that these polymers in acid form are stable up to 200^oC in nitrogen. Ion exchange capacity, water uptake, swelling, proton conductivity, and methanol permeability of the membranes were also investigated. The membrane shows lower water uptake, swelling and methanol permeability than that of the Nafion 115 membrane.

PRESENTER's name: Yuanqin Zhu