High-performing phenanthrene-containing poly(arylene piperidinium)s for anion exchange membranes

Incorporating fused benzene rings in backbones of anion conducting polymers may improve the properties of anion exchange membranes (AEMs). Here, we have
prepared and studied ether-free AEMs based on poly(arylene piperidinium)s containing up to 50% phenanthrene units. A series of terpolymers were prepared in superacid-mediated polyhydroxyalkylations of phenanthrene, p-terphenyl and N-methylpiperidone. In order to efficiently vary the ion exchange capacity (IEC), a series of quaterpolymers was also prepared by including 2,2,2-trifluoroacetophenone. These precursor polymers were quaternized and cast into AEMs, which showed an increasing level of phase separation and thermal stability with the phenanthrene content. The hydroxide conductivity of the AEMs was enhanced by the presence of phenanthrene and values up to 156 mS cm^–1 at 80 °C were reached. Furthermore, the AEMs showed a high alkaline stability with, e.g., a mere 5% ionic loss after storage in 2 M aq. NaOH for 15 days at 90 °C. The results demonstrate the positive effect of incorporating phenanthrene units in the polymer backbone on the properties of AEMs, thus providing a successful strategy design and develop AEMs incorporating fused benzene rings for alkaline electrochemical energy devices.