Fluorinated/non-fluorinated sulfonated polynaphthalimides as proton exchange membranes

Two -SO3H containing diamine monomers, 2,5-bis(4-amino-2-trifluoromethylphenoxy)benzenesulfonic acid and 2,5-bis(4-aminophenoxy)benzenesulfonic acid were successfully synthesized through a typical aromatic nucleophilic substitution reaction followed by a reduction reaction, respectively. Derived from the diamine monomers, two series of sulfonated naphthalic polyimides (polynaphthalimides) containing ether and ketone linkages were synthesized through a one pot polymerization reaction. Some properties including thermal stability, mechanical properties, water uptake, swelling dimensional ratio, methanol permeability, and proton conductivity were thoroughly investigated. Some exhibited attractive properties as proton exchange membranes. It was found that the fluorinated series (CF3-SPI-X) exhibited higher dimensional stability and lower methanol permeability in comparison with non-fluorinated ones (SPI-X) at the same -SO3H group content.