Functionalization of Poly(2,6-dimethyl-1,4-phenylene oxide)s with Hindered Fluorene Side Chains for Anion Exchange Membranes

Functionalization of poly­(2,6-dimethyl-1,4-phenylene oxide)­s (PPO) was achieved by grafting hindered fluorene-based side chains to PPO via the Suzuki–Miyaura coupling reaction using an appropriate catalyst/ligand system. Using the resulting functionalized PPO, anion-conductive copolymers, PPO with fluorene side chains with pendant alkyltrimethyl­ammonium groups, were synthesized via the Menshutkin reaction. The quaternized copolymers yielded ductile, transparent membranes which were soluble in dimethyl­formamide, dimethyl sulfoxide, and methanol at room temperature. The fluorene side chain containing membranes showed considerably higher hydroxide ion conductivities, up to 176 mS/cm at 80 °C, compared to that of typical anion exchange membranes based on the benzyl­trimethyl­ammonium motif. The results of titration and hydroxide ion conductivity measurements demonstrated excellent chemical stability of the fluorene side chain containing anion exchange membranes (AEMs), even after 1000 h immersion in 1 M NaOH at 80 °C. The results of this study suggest a new and scalable route for the functionalization of PPO and preparation of AEMs for practical alkaline fuel cell applications.