Résumé
Synthesis and the characterization of original polymer electrolyte membranes arising from fluorinated copolymers based on vinylidene fluoride (VDF) and hexafluoropropylene (HFP), grafted by aryl sulfonic acids is presented. They were obtained in a three step-process: i) the conventional radical terpolymerization of -trifluoromethylacrylic acid (TFMAA), VDF and HFP, initiated by peroxides led to original fluorinated functional terpolymers bearing carboxylic acid side groups in good yields. Molar masses, glass transition temperatures and decomposition temperatures (under air), determined by size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) were ranging between 10,000 and 21,400, from -27 to -18 °C, and from 140 to 275 °C, respectively; ii) the decarboxylation could be overcome by the reduction of these carboxylic acid dangling functions into hydroxyl ones, in the presence of AlLiH4; iii) the third step concerned an etherification reaction of such resulting secondary hydroxyl groups with parasulfonic phenol. Both these reactions did not affect the contents of fluorinated termonomeric units. The microstructures, physico-chemical, and thermal properties of the grafted materials were investigated by NMR and infrared spectroscopies, SEC and DSC, and TGA. Indeed, the molecular weights of the new terpolymers were similar as those of the precursors while their thermal stability was higher. Membranes incorporating these functional fluoropolymers were processed by casting and their electrochemical properties (ionic exchange capacity, proton conductivity, and swelling rates discussed, and compared to those of Nafion and to other fluorinated membranes.