Sulfonated polyimides and their polysilsesquioxane hybrid membranes for fuel cells

• Three sulfonated polynaphthalimides were successfully synthesized.
• Acid functionalized POSS was introduced to yield some novel hybrid membranes.
• It was found that isomeric structure could affect the properties of the membranes.
• Morphology was studied by SEM and EDX.

Three sulfonated polyimides, including a couple of isomeric polymers, were synthesized through a typical “one pot” polymerization reaction. Hybrid membranes were constructed by incorporating a multiple-acid functionalized polysilsesquioxane into the above polymers via a sol–gel process. The properties, including thermal stability, mechanical properties, water uptake, swelling ratio, methanol permeability and proton conductivity were evaluated. The proton conductivities of the membranes were above 0.11 S cm− 1 at 100 °C. Hybrid membranes exhibited the enhanced ability of water absorption and proton conducting. The methanol permeabilities of these membranes were 3.8–6.94 × 10− 7 cm2 s− 1, which were more competitive than Nafion 117. It was found that isomeric structure could affect the properties of both the pristine and hybrid membranes. The microstructures featured with phase-separation morphology could be observed in the hybrid membranes.