Sulfonated polyimide membranes: a new type of ion-conducting membrane for electrochemical applications

Abstract: The swelling and conductive properties of naphthalenic sulfonated polyimide (SPI) membranes were determined depending on the ionic content and the ion distribution along the polymer chain. The results combined with a structural study using small-angle neutron and X-ray scattering indicate that these materials have specific properties compared to other membranes. These polymers present a significant porosity in the dry state, the swollen state is not sensitive to external conditions, the water uptake per sulfonic group is constant varying the ionic content, the swelling is strongly anisotropic, concentrated along thickness and is not accompanied by structural modification in the in plane directions. The results indicate the existence of an anisotropic structure on the local scale along thickness formed during the film preparation. We propose that the structure is not formed of ionic domains dispersed in the polymer matrix but corresponds to disc-like hydrophobic domains spaced by a continuous ionic phase. The polymers can be thus considered as a new category of ion exchange membranes. Key words: 1