The activity of benzyl and allyl α-H sites in p-cresol-grafted fluorinated poly(aryl ether oxadiazole) toward the bromination reaction

The energy barrier for the bromination reaction of the benzyl α-H and allyl α-H sites of p-cresol-grafted fluorinated poly(aryl ether oxadiazole) was obtained using density functional theory calculations. The simulation results indicated that the energy barrier for the bromination reaction at the benzyl α-H site was 80.6 kcal mol^-1, while the corresponding value for the allyl α-H site was 88.4 kcal mol^-1, indicating that the former site was likely to be selectively brominated. This was confirmed by the bromination of p-cresol-grafted fluorinated poly(aryl ether oxadiazole) followed by ¹HNMR characterization. This result suggests that upon derivatizing benzyl α-H sites with a cation group (to yield an anion-exchange membrane), the allyl α-H sites would remain free for subsequent crosslinking. This result has positive implications for the synthesis of robust and crosslinked anion-exchange membranes based on this platform.