Fluorinated polymers based on pyrazole groups for fuel cell membranes

• Fluorinated copolymers bearing pyrazole group as precursor of proton-conducting membranes.
• 1-Benzyl-5-methyl-3-hydroxymethyl-pyrazole was synthesized and then grafted onto poly(CTFE-alt-IEVE) copolymer.
• Deprotection of the benzyl group produced poly(CTFE-alt-IEVE)-dep-pyrazoley% copolymers.
• NMR spectroscopy enabled to monitor all reaction steps.
• Copolymers processed into membranes with proton conductivity of 4 × 10−5 mS cm−1 at 180 °C.

The synthesis and characterization of two fluorinated copolymers bearing pyrazole group as precursor of proton-conducting membranes in polymer electrolyte fuel cells are described. 1-Benzyl-5-methyl-3-hydroxymethyl-pyrazole was first synthesized in a two step-reaction. It was then grafted onto poly(chlorotrifluoroethylene -alt-2-iodoethyl vinyl ether) copolymer (poly(CTFE-alt-IEVE)). The degree of grafting was controlled by the reaction time, and reached 30 and 55% after 24 and 48 h, respectively. Deprotection of the benzyl group produced poly(CTFE-alt-IEVE)-dep-pyrazoley% copolymers. NMR spectroscopy enabled to monitor all reaction steps and ensured the purity of these functional fluorinated copolymers. The poly(CTFE-alt-IEVE)-dep-pyrazoley% copolymers were thermally stable (up to 200 °C under air) and showed a maximum proton conductivity of 4 × 10−5 mS cm−1 at 180 °C under anhydrous conditions. From cyclic voltammetry (CV), these copolymers displayed an electrochemical stability domain extended over 2.0 V.

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