Preparation and behavior of “molecular compound” through covalent crosslinking between amino and sulfonic groups in single copolymers

4-Aminophenyl hydroquinone (4Am-PH), a bisphenol monomer, was synthesized and further reacted with bisphenol A (in three different molar ratios), 3.3′-disulfonated 4.4′-dichlorodiphenyl sulfone, and 4.4′-difluorobenzophenone to prepare three sulfonated poly(arylene ether ketone sulfone) copolymers with different amounts of pendant amino groups (Am-SPAEKS-1, Am-SPAEKS-2, and Am-SPAEKS-3), while the molar ratio of 3.3′-disulfonated-4.4′-diphenyl sulfone to 4.4′-difluoro diphenylmethanone was kept constant. Three crosslinked polymeric membranes (C–Am-SPAEKS-1, C–Am-SPAEKS-2, and C–Am-SPAEKS-3) with a varying degree of crosslinking were prepared by heating the corresponding Am-SPAEKS copolymers at 180 °C. 4Am-PH, Am-SPAEKS copolymers, and C-Am-SPAEKS membranes were characterized by Fourier transform infrared and ¹H NMR spectroscopy. Compared to non-crosslinked membranes, some properties of the crosslinked membranes are obviously improved, such as dimensional stability, oxidative stability, methanol resistance capacity and mechanical stability. The proton conductivity of C-Am-SPAEKS-2 membrane reaches a value of 0.089 S cm⁻¹, which is higher than those of SPAEKS and Am-SPAEKS-2 at 120 °C. These results indicate the C-Am-SPAEKS crosslinked polymeric membranes are suitable candidate for applications in proton exchange membrane fuel cells.