Highly sulfonated co-polyimides containing hydrophobic cross-linked networks as proton exchange membranes

A novel diamine monomer bearing double hydrophobic cross-linkable tetrafluorostyrol side-groups has been successfully synthesized. Based on this monomer along with 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), a series of cross-linked highly sulfonated co-polyimide (CSPIy-6FATFVPx) membranes with IEC values ranging from 2.07 to 2.41 meq g−1 were prepared via a high temperature poly-condensation, followed by a thermal cross-linking reaction. The SPI were synthesized by high temperature polymerization. The CSPI membranes were obtained from the SPI membrane by thermal crosslinking reation. The polymerization and crosslinking reation were not performed in one pot. The CSPIy-6FATFVPx membranes showed significantly excellent performance, especially the high proton conductivity (0.153–0.210 S cm−1 at 80 °C), low water uptake (54.1%–87.1% at 80 °C) and swelling ratio (15.5%–23.0% at 80 °C). Furthermore, the CSPIy-6FATFVPx membranes also exhibited outstanding thermal stability (5% weight loss when the temperature exceed 320 °C), excellent hydrolytic stability and mechanical properties. The results indicate that CSPIy-6FATFVPx are promising candidates as proton exchange membranes in fuel cell technology.