Water-soluble thermoresponsive poly(γ-4-methylbenzyl-L-glutamate) bearing Y-shaped (i.e., oligo-ethylene-glycol and alkyl groups, such as 1-butyl, 1-hexyl, or 1-dodecyl) and triazolium tetrafluoroborate side-chains (PMBLG-OEG7/Cm-BF4, m = 4, 6, and 12) have been prepared by nucleophilic substitution of poly(γ-4-methylbenzyl-L-glutamate)-oligo-ethylene-glycol conjugates (PMBLG-OEG7) and various 1-alkyl bromide and ion-exchange reactions of triazolium bromide and NaBF4. Poly(γ-4-chloromethylbenzyl-L-glutamate) (PCMBLG) was derivatized into poly(γ-4-azidomethylbenzyl-L-glutamate) (PAMBLG), followed by reaction with propargyl functionalized polyethylene glycol monomethylether 350 (Pr-OEG7) via a copper-mediated 1,3-dipolar cycloaddition to yield PMBLG-OEG7. PMBLG-OEG7/Cm-BF4, m = 4, 6, and 12) adopted an α-helical conformation and showed lower critical solution temperature (LCST)-type phase behaviors in aqueous solutions. The cloud point temperature (Tcp) was significantly decreased with an increase in polymer concentration and salt (e.g., NaBF4) concentration. Elongating the alkyl chain length can further decrease the Tcp.
High hydroxide conductivity and sufficient dimensional/alkaline/mechanical stability are highly desired for practical applications of anion exchange membranes (AEMs). Herein, a new di -quaternized side-chain precursor (EDQA) was firstly designed and synthesized. Then novel AEMs (DBTF-4QA-x) based on poly(fluorenylene alkylene)s containing dual Y-shaped side-chains were prepared from EDQA by an efficient click reaction. Benefiting from several structural advantages of EDQA, DBTF-4QA-x membranes possessed high hydroxide conductivities up to 154.8 mS cm −1 at 80 °C, while maintained high dimensional stability. The membranes exhibited robust mechanical properties with tensile strengths and elongation at break up to 107.4 MPa and 46.4%, respectively. Furthermore, the membranes showed high alkaline stability with the conductivity loss below 11.4% after immersing in 4 M aq. NaOH at 80 °C for 40 days. In addition, DBTF-4QA-0.5 membrane achieved the maximum peak power density of 836.4 mW cm −2 in H 2 /O 2 fuel cells at 60 °C.
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