Fluoropolymers and membranes prepared from such polymers, in particular for fuel cells and method for synthesizing such polymers

The synthesis and the characterization of new polymer electrolyte membranes based on fluoropolymers grafted by aryl sulfonic acids is presented. They are obtained in a three step-process. First, the radical terpolymerization of a-trifluoromethylacrylic acid (TFMAA), vinylidene fluoride (VDF) and Hexafluoropropene (HFP) , initiated by 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane led to original fluoropolymers bearing carboxylic acid side functions in good yields. The structure and the properties of the materials were studied. Interestingly, poly((VDF-alt-TFMAA)-co-HFP) terpolymers containing alternation of VDF and TFMAA were produced, the termonomer contents of which, were assessed by 19F NMR spectroscopy. Molar masses and glass transition temperatures were ranging between 10,100 and 21,400, and from –27 to –18 °C, respectively. In a second part, the carboxylic functions of these terpolymers were reduced with AlLiH4 followed by an etherification reaction with the sulfonic phenol. Both these reactions did not modified the contents of termonomers as evidenced by 1H, 19F, 13C NMR. The physico-chemical properties of the grafted materials were investigated by NMR and Infrared spectroscopies, SEC, DSC and TGA and are reported. Membranes incorporating these functional fluoropolymers were prepared and the electrochemical properties (IEC, proton conductivity, swelling rates) were studied, discussed, and compared to those on Nafionâ