Synergistically Functionalized Pyridinyl- and Phosphine-Oxide-Based Semifluoro-Sulfonated Copolytriazole Membrane Preparation via “Click” Polymerization for Proton Exchange Membrane Applications

Both pyridinyl- and phosphine-oxide-based aromatic polymers exhibit outstanding properties for proton exchange membrane (PEM) applications, making them alternative high-performance polymers. Herein, we have first designed and synthesized a series of pyridinyl and phosphine oxide moieties containing semifluoro-sulfonated copolytriazoles (PYPOSSH-XX) with different degrees of sulfonation by the “Click” polymerization reaction. The structure of high molecular weight polymers (weight-average molecular weight M_w: 126–274 kDa) was confirmed by FTIR and NMR (¹H, ¹³C, ¹⁹F, ³¹P) spectroscopic analysis. These newly synthesized copolymers exhibited good solubility in the selective organic solvents. The copolymers possess high thermal stability (T_d10 > 280 °C) and efficient mechanical characteristics along with a high storage modulus value (2000–7900 MPa). The solution-fabricated copolytriazole films hold balanced water uptake (WU) and swelling ratio (SR) values that are essential for actual PEM applications. The microscopic FESEM cross-sectional investigation of cryofractured films depicted a compact and dense bulk microstructure necessary to prevent fuel gas crossover. The nanophase AFM topology images confirm a well-segregated and interconnected hydrophobic–hydrophilic phase-separated morphology, which helps for the formation of a fruitful ion conduction pathway. These semifluoro-sulfonated copolymer films displayed high proton conductivity between 24 and 128 mS/cm at 90 °C. The films also exhibited superior oxidative stability (τ ≥ 26 h) in Fenton’s reagent at 80 °C. These materials combine high thermal and mechanical stability, high proton conductivity, and superior oxidative stability of the newly synthesized polymers, inferring that the present materials are attractive ionomer membranes for potential PEM applications.