Novel cross-linked anion exchange membranes with diamines as ionic exchange functional groups and crosslinking groups

• Two novel cross-linked anion exchange membranes were synthesized via nucleophilic substitution reactions.
• The synthesis routes simplified by rolling the crosslinking and functionalizing into one.
• The crosslinking process enhanced the thermal and mechanical stabilities of membranes.
• The thermal properties and durability of membranes in alkaline environments were enhanced.
• The extensive conjugated structures of precursory polymer dispersed the electronic distributions of quaternary ammonium groups.

Two novel cross-linked anion exchange membranes (AEMs) for alkaline fuel cells (AFCs) were synthesized via nucleophilic substitution reactions. Brominated poly(2,5-bis(perfluorophenyl)-1,3,4-oxadiazole-co-allyl bisphenol), called as precursory polymer (PP), was synthesized by reaction of 2,5-bis(2,3,4,5,6-pentafluorophenyl)-1,3,4-oxadiazole (FPOx) and diallyl bisphenol A (DABPA) followed by bromination. Ethanediamine (EDA) and propane diamine (PDA) were introduced to PP to obtain cross-linked polymers EDA-PP and PDA-PP, respectively. The reactions between PP and diamines rolled the crosslinking and functionalizing process in one. The crosslinking process enhanced the thermal and mechanical stabilities of EDA-PP and PDA-PP, which were affected by the length of alkyl chains of diamines. Meanwhile, the conjugated system of PP extended the electron clouds around the amine groups, which improved the thermal stability and alkaline durability of quaternary ammonium (QA) groups. The solution casting membranes of EDA-PP and PDA-PP showed high ionic conductivities. The swelling ratios, TGA and AFM properties of the membranes also demonstrated their good mechanical and thermal stabilities.