Novel sulfonated poly(arylene biphenylsulfone ether) copolymers containing bisphenylsulfonyl biphenyl moiety: Structural, thermal, electrochemical and morphological characteristics

A series of sulfonated poly(arylene biphenylsulfone ether) polymers containing up to two pendant sulfonic acid groups per repeat unit were successfully synthesized from 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl (BCPSBP), disodium 3,3'-disulfonate-4,4'-dichlorodiphenylsulfone (SDCDPS) and bisphenol A via aromatic nucleophilic displacement polycondensation. The resulting polymers were characterized by means of Fourier transform infrared and ¹H NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis (TGA). The number-average molecular weight (M_n) of the synthesized polymers was in the range 15 300-22 900 g mol^-1, and the polydispersity indices (M_w/M_n) varied from 2.5 to 4.4. Tough membranes with SDCDPS/BCPSBP mole ratio up to 50:50 were successfully cast using N-methyl-2-pyrrolidone (NMP). An increase of sulfonic acid groups in the polymer backbone resulted in increased solubility in aprotic polar solvents and glass transition temperature. The TGA curves of all the copolymers in acid form exhibited two distinct weight-loss profiles. The influential characteristics of the polymer electrolyte membranes, such as tensile strength, water uptake, ion-exchange capacity and proton conductivity, were characterized with respect to the pendant sulfonic acid groups. Atomic force microscopy phase images of the acid-form membranes clearly showed the hydrophilic domains, with sizes increasing as a function of the degree of sulfonation.