High‐performance blended membranes based on poly(arylene ether sulfone) and sulfonated poly(styrene‐isobutylene‐styrene) for direct methanol fuel cell applications

Abstract In this study, two series of poly(arylene ether sulfone)s (PAES) with hydrophobic blocks made of 4,4′‐dihydroxyphenyl (BP) and 2,2‐bis(4‐hydroxyphenyl) propane (BPA) were synthesized. The copolymers were prepared by a coupling reaction between decafluorobiphenyl (DFBP) end‐capped nonsulfonated block (PAES A or B) and sulfonated block (SPAES B). The reactive behavior of DFBP facilitates the low‐temperature coupling reaction (below 105°C). The final copolymers were blended at distinct weight percent ratios (0, 20, 30, and 40) with poly(styrene‐b‐isobutylene‐b‐styrene) (SIBS) at a sulfonation level of 88% to obtain strong and flexible membranes. Morphological, thermal stability, and conduction properties of the resulting membranes were measured and reported here. Results suggest that phase segregation between hydrophobic and hydrophilic domains occurs below 1 meq. g −1 ion exchange capacity. These membranes have low water absorption and high thermal stability. Incorporating SIBS 88 into the blend added elastomeric behavior enhancing transport properties and additional ionic domains, achieving proton conductivities of 0.21 S cm −1 for BPA‐based membranes at 50°C (40% SIBS 88). The selectivity of the studied membranes surpasses Nafion® 117, making them strong candidates for proton exchange membranes in direct methanol fuel cell applications.