Synthesis and properties of highly branched sulfonated poly(arylene ether)s as proton exchange membranes

A series of branched sulfonated poly(arylene ether)s were successfully synthesized using 1,3,5-tris[4-(4-fluorobenzoyl)phenoxy]benzene (B3) as branching agent. The synthesized branched copolymers were soluble in polar organic solvents, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc) and dimethylsulfoxide (DMSO), and could be cast to form tough and smooth films. The effect of degree of branching (DB) on the proton conductivity, swelling ratio and oxidative stability of the membranes was investigated. With increasing DB value, the proton conductivity and oxidative stability of the membranes increased. A maximum oxidative stability of the branched membrane with 4% of DB value was determined to be 3.4 times larger than that of the linear membrane. In addition, as the DB value increased, the swelling ratio of the membranes decreased from 13.51% to 9.09% at 80 °C. The results indicated that increasing DB value might be an effective way to improve the properties of proton exchange membranes.