Comb-Shaped Poly(arylene ether sulfone)s as Proton Exchange Membranes

Abstract

A new sulfonated side-chain grafting unit containing two or four sulfonic acid groups was synthesized using sulfonated 4-fluorobenzophenone (FBP) and 1,1-bis(4-hydroxyphenyl)-1,4-((4-fluorophenyl)thio)phenyl-2,2,2-trifluoroethane (3FBPT). A conventional aromatic nucleophilic substitution (SNAr) was used for copolymerization of poly(arylene ether sulfone) containing a methoxy group. After converting the methoxy group to the reactive hydroxyl group, this functionalized copolymer was reacted to graft the sulfonated side chains to make the comb-shaped sulfonated poly(arylene ether sulfone) copolymers. All the polymers were characterized by 1H NMR, thermogravimetric analysis (TGA), the water uptake, and proton and methanol transport for fuel cell applications. These comb-shaped sulfonated polymers had good properties as polyelectrolyte membrane materials. The comb-shaped copolymers with two or four sulfonic acid groups show high proton conductivity in the range of 34−147 and 63−125 mS/cm, respectively. The methanol permeabilities of these copolymers were in the range of 8.2 × 10-7−5.6 × 10-8 cm2/s. A combination of high proton conductivities, low water uptake, and low methanol permeabilities for some of the comb-shaped copolymers indicated that they are good candidate materials for proton exchange membrane in fuel cell applications.