Synthesis and characterization of a new block copolymer for proton exchange membrane

A novel sulfonated block copolymer was prepared based on poly(arylene ether sulfone) (PAES) and carboxyl terminated polybutadiene (CTPB) and subsequently selective post-sulfonation of flexible polybutadiene block of copolymer was carried out because of great reactivity of double bonds to sulfonating reagent. Successful introduction of sulfonate groups into double bonds was confirmed by 1H NMR and FT-IR. Analysis by transmission electron microscopic (TEM) and X-ray diffraction (XRD) showed that sulfonated poly(arylene ether sulfone)-b-polybutadiene (SPAES-b-PB) with different degree of sulfonation (DS) exhibited very different microstructures. The glass transition temperature and thermal stability of SPAES-b-PB membranes were studied by DSC and TGA. Complex impedance measurement has shown that a SPAES-b-PB membrane exhibits high conductivity (0.0302 S/cm, 25 °C) even with relatively low DS (11.5%). Study of relationship between properties and structures of sulfonated copolymer membranes showed that high flexibility of sulfonated block was helpful for sulfonate groups to move together to form ionic clusters, which connected with each other to form continuous ionic networks.