Aromatic polymers (AP), like poly(ether ether ketone), polysulfone, and poly(p-phenylene oxide) are very well known and versatile high-temperature engineering resins. The introduction of cationic groups, like quaternary ammonium moieties, leads to the formation of anionic exchange membranes, while the functionalization with acidic groups, like sulfonic acid, forms proton and cation exchangers. The so formed ionic conducting polymers are very versatile materials used in several applications such as proton and anion exchange membrane fuel cells or redox-flow batteries. These materials must operate in an aggressive environment and under harmful experimental conditions and their application depends greatly on the enhancement of the stability.
We have in recent years concentrated on the improvement of existing separators, introducing Van der Waals bonds (organic-inorganic Class I hybrids) or covalent bonds (“cross-links” or Class II hybrids) reporting different methods for the functionalization of polyarylene systems. The continuous optimization of synthesis parameters, the choice of different polymers and/or functionalization groups and the improvement of casting procedures and treatments of membranes, led to good results in terms of ionic conductivity, selectivity and stability.
In this presentation, we will focus the attention on the comparison of the synthetic approach for the functionalization of the two classes of anion and cation exchange membranes based on AP. The results will be discussed in terms of conductivity, mechanical and thermal behavior, water uptake, permeability, and stability.