The effects of humidity on gas transport properties of sulfonated copolyimides

Hydrogen, oxygen and carbon dioxide transport properties are studied at various hydration rates for a large series of sulfonated copolyimides synthesized with a naphthalenic dianhydride, a sulfonated diamine and various non-sulfonated diamines. For all copolymers, the gas permeability coefficient decreases when the relative humidity increases in the range 0–70% and an increase of gas flux is observed at high hydration. The magnitude of the permeability coefficient variation depends on the gas polarity and on the copolymer composition. A detailed analysis of the gas transport properties at anhydrous state and of the water sorption mechanism as a function of the copolymers composition allows to explain all the gas permeability variations as a function of hydration.