Tuning Ion Exchange Capacity in Hydroxide-Stable Poly(arylimidazolium) lonenes: Increasing the Ionic Content Decreases the Dependence of Conductivity and Hydration on Temperature and Humidity

Increasing the ion exchange capacity (IEC, mmol.g(-1)) of anion exchange membranes (AEMs) decreases the dependence of ionic conductivity (sigma) and ion pair hydration on limiting conditions of temperature and humidity. We present novel, hydroxide-stable polycationic ionenes having penta-substituted imidazolium repeating units. Variation of N,N'-dialkyl substituents having 1-4 carbons yields a range in IEC(Cl) (1.56-2.32 mmol.g(-1)). The trend of sigma((Cl)) similar to IEC is in agreement with comparable poly(arylimidazolium)s. This is the first report crosscorrelating water uptake (WU) and ionic conductivity of a homologous series of poly(arylimidazolium) ionenes. The AEMs of higher IEC have a lower range in sigma and hydration number (lambda = WU/IEC) within limits of temperature and humidity. Decreasing IEC correlates to increasing effective activation energy of ion transport (E-a(eff.)), at constant hydration. The AEM of N,N'-dimethyl-2,4,5-arylimidazolium repeating units and the highest IEC provides sigma((Cl)) = 12 mS.cm(-1) (80 degrees C, 95 RH%) and sigma((OH)) = 120 mS.cm(-1) (40 degrees C, 90 RH%).