Preparation and Alkali Resistance Research of Cyclotriphosphazene Based Hexa‐Imidazole Compound Functionalized Addition‐Type Polynorbornene Anion Exchange Membranes

ABSTRACT Anion exchange membranes (AEMs) are extensively utilized across various domains due to their remarkable performance. Nonetheless, AEMs continue to encounter significant challenges related to thermal stability, alkaline stability, and ion conductivity. Advanced molecular design and the precise incorporation of functional groups are pivotal for enhancing their properties. In this work, norbornene monomer was produced from 5‐norbornene‐2‐methanol. One monomer featured an extensive alkyl side chain, while the other included a long bromine side chain. These monomers were subsequently used to synthesize a functional diblock polynorbornene copolymer. Finally, cyclotriphosphazene based hexa‐imidazole compounds were designed using cyclotriphosphazene groups and crosslinked with long, flexible side chains by the Menschutkin reaction. The flexible side chain structure and block structure effectively promoted phase separation, while the high concentration of imidazole ion groups facilitated aggregation into distinct ion domains. As a result, a series of anion exchange membranes (aPNB‐CTPP‐2MI‐x) fabricated using this approach demonstrated excellent ionic conductivity, alkaline, and heat resistance. Notably, the aPNB‐CTPP‐2MI‐1.75 membrane achieved an ionic conductivity exceeding 100 mS cm −1 at 80°C, with a swelling degree of only 11.96%. Even after 576 h of immersion in 1 M NaOH solution (80°C), the ionic conductivity remained above 86.83%.