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.