Hydrophobic Effect on Alkaline Stability of Graft Chains in Ammonium‐type Anion Exchange Membranes Prepared by Radiation‐Induced Graft Polymerization

Vinylbenzyltrimethylammonium hydroxide (VBA) and styrene (St) cografted poly(ethylene‐co‐tetrafluoroethylene) anion exchange membranes (VBA/St‐AEM) were prepared by the radiation‐induced graft polymerization of chloromethylstyrene and St and sequential quaternization and anion exchange reactions. Increasing the St content in the grafts to 63 % resulted in a gradual 21 % and 34 % decrease in the conductivity and water uptake, respectively, compared to those in the VBA‐homo‐grafted AEM. AEMs with a higher St content (81 %) showed a 9 % and 18 % higher conductivity and water uptake, respectively. Small‐angle neutron scattering showed that the sudden growth of “water puddles” consisting of water‐rich nano‐domains dispersed randomly in phase‐separated hydrophilic ion channels enhanced the conductivity and water uptake. In the alkaline durability test of VBA/St‐AEM in 1 M potassium hydroxide at 80 °C for 720 h, the loss of the conductivity was suppressed from 43 % to 8 %, when the St contents in the grafts were increased from 0 % to 63 %. Vinylbenzyltrimethylammonium hydroxide and styrene cografted poly(ethylene‐co‐tetrafluoroethylene) anion exchange membranes (VBA/St‐AEM) were prepared. The conductivity and water uptake of VBA/St‐AEM decreased with increasing styrene content in the range of 0–63 %. However, VBA/St‐AEM with the 81 % molar ratio of styrene exhibited higher conductivity and water uptake. The hydrophobic styrene in the graft chain enhanced the alkaline stability of VBA/St‐AEM.