Development and characterization of ion-exchange polymer blend membranes

Abstract

In the presented paper, the preparation and characterization of new ionomer blend membranes containing sulfonated poly(etheretherketone) PEEK Victrex® is described. The second blend components were Polysulfone Udel®-ortho-sulfone-diamine, polymide PA Trogamid P (producer: Huls) and poly(etherimide) PEI Ultem (producer: General Electric). In the blend membranes swelling was reduced by specific interaction, in the case of the blend components PA and PEI hydrogen bonds, and in the case of the blend component PSU–NH2 (partial) polysalt formation, leading to electrostatic interaction between the blend component macromolecules, and hydrogen bonds. The acid–base interactions also led to decrease of ionic conductivity by partial blocking of SO−3 groups for cation transport, compared with the ionic conductivity of the hydrogen bond blends. The acid–base blends showed better ion permselectivities than the hydrogen bond blends, even at high electrolyte concentrations, and thus better performance in electrodialysis. The thermal stability of the investigated blends was very good and in the case of the acid–base blends even better than the thermal stability of pure PEEK–SO3H. DSC traces of the blend membranes showed only one Tg. In addition, the membranes are transparent to visible light. But therefrom it cannot be concluded that the blend components are miscible to the molecular level: at the acid–base blend blends, the Tg of PEEK–SO3H is very similar to the Tg of PSU–NH2, and in the investigated hydrogen bond blends, the portion of PA or PEI, respectively, might be too low to be detected by DSC. The investigated blend membranes showed similar performance as the commercial cation-exchange membrane CMX in electrodialysis (ED) application. The performance of the acid–base blend membrane is better than the performance of the hydrogen bonded PEEK–PA blend, especially in the ED experiment applying the higher NaCl concentration. This is mainly due to the lower swelling and thus better ion permselectivity of the acid–base blend membrane, compared with the PEEK–PA blend. To get a deeper insight into the microphase structure of the investigated blends, dynamic mechanical analyses and TEM investigations of the prepared blend membranes are planned. In addition, due to their promising properties, the preparation of arylene main-chain acid–base blends with other polymeric acidic and basic components is planned. Furthermore, the acid–base blend membranes will be tested in H2 polymer electrolyte fuel cells and direct methanol fuel cells, because preliminary tests have shown that they have a good perspective in this application.