Sulfonated and Fluorinated Aromatic Terpolymers as Proton Conductive Membranes: Synthesis, Structure, and Properties

We designed and synthesized a series of sulfonated terpolymers, SPP-PQP and SPP-BQP, containing sulfophenylene, quinquephenylene (QP) and perfluoroalkylene (PAF) or hexafluoroisopropylidene (BAF) groups whose compositions were optimized to achieve high-performance proton conductive membranes. In both series, the terpolymers were obtained as high-molecular-weight (Mn = 19.032.9 kDa, Mw = 99.9198 kDa) providing bendable and transparent membranes with supposed ion exchange capacity (IEC) values (2.412.68 meq. g-1) by solution casting. SPP-PQP membranes exhibited higher water uptake, higher proton conductivity, and larger strain at break with increasing the PAF composition. In contrast, the membrane properties were less sensitive to the composition in the SPP-BQP membranes. Among the terpolymer membranes investigated, SPP-PQP50 showed the best-balanced properties in terms of low water uptake, high proton conductivity, and high mechanical properties probably because highly hydrophobic aliphatic PAF and more rigid QP groups both contributed to those relevant properties. Overall, the combination of different hydrophobic components in the terpolymers was effective in improving the properties of proton conductive membranes, that could not be achieved with the corresponding copolymer membranes.