Synthesis and properties of cis/trans mixtures of bis(4-hydroxyphenyl)-1, 2-diphenylethylene containing sulfonated poly(ethersulfone)s proton exchange membranes

Abstract Conjugated cis/trans isomer-based polymer membranes were prepared with 15–25 mol% of bis(4-hydroxyphenyl)-1,2-diphenylethylene ( BHDPE ). BHDPE has a conjugated nonplanar conformation structure containing the peripheral four aromatic rings which facilitate the formation of π-π interactions. A series of sulfonated poly(ethersulfone)s ( S-PBHDPE ) was synthesized with concentrated sulfuric acid. The sulfonation took place selectively on the BHDPE unit, and simultaneously on the side-chain and main-chain phenyl groups. The S-PBHDPEs consisted of a 4:6 ratio of cis and trans form mixtures. The S-PBHDPE membrane structures and characteristics were evaluated by 1 H NMR spectroscopy, and their thermal stabilities evaluated. The ion exchange capacity (IEC), water uptake (WU) and proton conductivity of the membranes were evaluated as a function of the molar percentage of the sulfonic acid group. The WU of the synthesized S-PBHDPE membranes ranged from 21 to 52%, compared with 28% for Nafion 211 ® . The S-PBHDPE membranes exhibited proton conductivities (80 °C, RH100) of 42.7–125.6 mS/cm, compared with 137.4 mS/cm for Nafion 211 ® . The surface morphologies of S-PES 40 and S-PBHDPE 20 membranes were studied by AFM images.