Anion conducting multiblock copolymers with different tethered cations

Abstract

ABSTRACTA multiblock copoly(arylene ether) polymer was used to quantitatively compare the ion conducting channels formed by three different, tethered cation head‐groups. The synthesis allowed for the formation of an exact number of tethers on each repeat unit. Three head‐groups, quaternary trimethylammonium (TMA), quinuclidium (ABCO), and tris(2,4,6‐trimethoxyphenyl)phosphonium (TTMPP) cation head‐groups were compared in terms of size of the conducting channels, ionic conductivity of the mobile hydroxide ion, mechanical properties, quantity of productive and unproductive water, and chemical stability of the membrane in base. The interdomain spacing showed that multiblock copolymers with larger cations formed larger ion conduction channels in the membrane. Larger cations resulted lower ion exchange capacity (IEC) even though the polymer backbone and tether arrangements were identical. TMA was the most stable cation after exposure to 1 M NaOH at 60 °C for 20 days. ABCO had a lower number of bound water molecules and a 22% loss in ion conductivity after treatment in 1 M NaOH at 60 °C for 20 days due to the higher hydroxide ion concentration in the ion conductive blocks. Membranes with TMA head‐groups also had the best mechanical properties. Two membrane preparation methods were compared. The presence of the cation head‐groups assists in phase segregation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1395–1403