Solid State Ionics, Vol.317, 108-114, 2018
Synthesis and characterization of new fluorinated copolymers based on azole groups for fuel cell membranes
Two new fluorinated copolymers synthesized by grafting omega-hydroxyl pyrazolic (Trip) and triazolic (Trit) tripods onto poly(chlorotrifluoroethylene-alt-2-iodoethyl vinyl ether) copolymer (poly(CTFE-alt-IEVE) are reported. These copolymers were prepared in two steps: the co-hydroxy nitrogenous heterocycles reacted with iodine atoms of poly(CTFE-alt-IEVE) copolymer followed by the deprotection of the benzyl group. The chemical structures of tripod monomers and resulting copolymers were characterized by nuclear magnetic resonance and infrared spectroscopies, elemental analysis, and mass spectrometry. The first analysis allowed one to determine the degree of grafting that reached 80 and 19% for copolymers bearing pyrazole and triazole, respectively. Membranes were processed in pellet form by compressing these copolymers. Thermal properties of the membranes, examined by thermogravimetric analysis and differential scanning calorimetry, showed that such copolymers were thermally stable up to 200 degrees C under air, and exhibited glass transition temperatures ranging between 31 and 47 degrees C. The temperature dependence of conductivity led to a simple Arrhenius behavior for both copolymers. Poly(CTFE-alt-IEVE)-dep-Trit(19%) and poly(CTFE-alt-IEVE)-dep-Trip(80%) copolymers had a maximum proton conductivity of 1.3 10(-3) and 5.91 10(-)(5) mS/cm respectively at 180 degrees C under quasi-anhydrous conditions. Cyclic Voltammetry (CV) study illustrated that the electrochemical stability domain for poly(CITE-alt-IEVE)-dep-Trip(80%) and poly(CTFE-alt-IEVE)-dep-triazole(28%) copolymers extended 2.0 V.