Influence of the hydroquinone with different pendant groups on physical and electrochemical behaviors of directly polymerized sulfonated poly(ether ether sulfone) copolymers for proton exchange membranes

Three series of sulfonated poly(ether ether sulfone) (SPEES) copolymers with controlled degrees of sulfonation (DS) were prepared by aromatic nucleophilic polycondensation of disodium 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), 4,4′-dichlorodiphenylsulfone (DCDPS) and three hydroquinone with different pendant groups (hydroquinone (HQ), tertbutylhydroquione (TBHQ) and p-toluhydroquinone (PTHQ)). Synthesized sulfonated copolymers were characterized by FT-IR, TGA and DSC. Moreover, the microstructure of membrane was investigated by TEM. All copolymers had high molecular weight and could be cast into tough membranes. Performances of all membranes were studied thoroughly. The copolymers with different bisphenol structures show different physical and electrochemical behaviors, such as water retention, glass transition temperature (T_g) and proton conductivity, etc. Water retention and proton conductivity of SPEES membranes with tertbutylhydroquione were much better than other series membranes with same DS because of the hydrophilic channel formed by bulk pendant groups.