Polyelectrolyte proton exchange membranes: synthesis and characterization of sulfonated polyimide membranes using novel stilbene-containing diamine

Abstract

A new unsymmetrical diamine, 4-(2-aminophenoxy)-4′-aminostilbene was successfully synthesized and used to synthesize stilbene-containing sulfonated polyimides. 2,2′-Benzidine-disulfonic acid, 1,4,5,8-naphthalene tetracarboxylic dianhydride and different mole ratios of 4-(2-aminophenoxy)-4′-aminostilbene and 2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane were used for the synthesis of stilbene-containing polyimides with sulfonic acid groups. The synthesized polymers were characterized using various physicochemical characterization techniques such as nuclear magnetic resonance spectroscopy, infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and electrochemical impedance spectroscopy. Furthermore, the viscosity, water uptake, ion exchange capacity, swelling ratio, hydrolytic stability, oxidative stability, mechanical properties and proton conductivity of the synthesized membranes were also analyzed. Sulfonated polyimide membranes showed a water uptake capacity of 18.93–28.89%, proton conductivity of 0.028–0.039 S cm−1 at 30 °C, ion exchange capacity of 1.469 meq g−1 and hydrolytic stability of 40–44 h at 80 °C. The solubility of the sulfonated polyimide membranes was improved when unsymmetrical diamine was used to prepare sulfonated polyimides.