Polymer electrolyte membranes based on cross-linked highly sulfonated co-polyimides

Abstract A novel diamine monomer 3,3′-Bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)biphenyl-4,4′-diamine (TFVBPA) bearing double hydrophobic cross-linkable tetrafluorostyrol side-groups has been successfully synthesized via a nucleophilic substitution reaction. A series of cross-linked highly sulfonated co-polyimide (CSPIy-TFVBPAx) membranes with ion-exchange capacity (IEC) values ranging from 2.27 to 2.44 meq. g −1 have been prepared from this monomer. The CSPIy-TFVBPAx membranes show excellent comprehensive properties, especially the high proton conductivity (0.135–0.190 S cm −1 at 80 °C), low water uptake (60.9–76.7% at 80 °C) and swelling ratio (14.2–19.6% at 80 °C). Moreover, the CSPIy-TFVBPAx membranes also exhibit outstanding thermal stability (5% weight loss temperature exceed 320 °C) and excellent hydrolytic stability. The results indicate that the CSPIy-TFVBPAx membranes are promising candidates for proton exchange membranes in fuel cell applications.