Synthesis and characterization of novel cardo poly(aryl ether sulfone) bearing zwitterionic side groups for proton exchange membranes

A novel series of sulfonated poly(aryl ether sulfone)s with zwitterionic groups (-CH₂CH₂CH₂N⁺CH₃(CH₂CH₂SO₃⁻)₂]) have been prepared by the copolycondensation of a secondary amine-containing biphenol monomer with 4,4′-biphenol and 4,4′-dichlorodiphenylsulfone, and this was followed by the reaction with sodium 2-bromoethanesulfonate. All the resulting copolymers can form uniform and tough membranes by simple solution casting. The investigation of ion exchange capacity (IEC) values indicated that each ammonium group interacted with one sulfonate group. Because of strong intermolecular interaction, the increased packing density of chain formed that resulted in polymer membranes with lower water uptake and swelling ratio, and better oxidative stability compared with side-chain-type sulfonated poly(aryl ether sulfone)s with the close IEC values. The polymer membranes bearing zwitterionic groups kept intact in Fenton’s reagent at 80 °C for 20 h. Furthermore, these membranes demonstrated higher proton conductivity than the side-chain-type sulfonated polymer membranes at the same measurement conditions.