M@TP

Poly(arylene piperidinium) (PAP) polymers have emerged as promising candidates for applications as anion exchange membranes (AEMs) and have seen some commercial use in the form of PiperION by Versogen; however, PiperION contains fluorinated units to balance its ionic content. Fluorine-free variants are environmentally more friendly alternatives as recycling is facilitated. Herein, we report a series of four fluorine-free PAP membranes that are mechanically robust and feature moderate water uptake yet high ionic conductivity. p-Quaterphenyl (pQP) is copolymerized with either m- or p-terphenyl (m/pTP) and N-methyl-4-piperidone under superacid-catalyzed polyhydroxyalkylation conditions. The molar ratios of the reactants are adjusted to maintain a balance of solubility and flexibility of the polymers and to reach ion exchange capacities between 2.53 and 2.66 mequiv g^-1. The polymers exhibit thermal stability of T_d,95 > 260 °C, Young's moduli between 0.7 and 1.0 GPa, and ultimate tensile stresses of 50-60 MPa in the dry state. Additionally, under submersion tensile deformation, the Young's moduli and ultimate tensile stresses are in the range 200-320 MPa and 15-22 MPa, respectively. The sample with an equimolar ratio of pQP and mTP was found to exhibit a robust nature with elongation up to 170% when subjected to submersion tensile deformation, thus showing attractive mechanical properties under relevant working conditions. Wet membranes show an ionomer SAXS peak in the range of 5 nm, suggesting clustering of water and ionic parts of the chain. High hydroxide conductivity of up to 197 mS cm^-1 at 80 °C is observed. Such behavior is promising considering their water uptake of 85% at 80 °C as an upper limit, resulting in moderate areal and through-plane swellings of 100% and 55%, respectively. The results demonstrate that fluorine-free PAPs can be tuned to match important criteria of AEMs, including low water uptake, high dimensional and alkaline stability, and high hydroxide conductivity.