Résumé
The membrane must fulfill drastic requirements: high ionic conductivity and stability to HO° radicals. Membranes for cars must withstand their properties at 120 °C for about 5000 h. The membrane is a functional polymer which bears protonic, cationic or anionic groups depending on the choice of use. Fluorinated polymers1 that possess protogen groups are suitable candidates. Various strategies have been proposed and well reviewed: -either by « direct » radical copolymerization of fluoroolefins bearing protogen groups2, -or by chemical modifications fluoropolymers3 The first strategy has already led to various commercailly available products such as Nafionâ , Flemionâ, 3Mâ Membrane, HyflonâIon, Aciplexâ and othersref. Cure site monomers, H2C=CHC6F12Br10, have also been involved in the terpolymerization of PFSFVE and fluorolefins for original crosslinked membranes. In addition, Mac Grath et al.7 have used or original polymers synthesized by polycondensation bearing perfluorinated aromatic rings. But, these perfluorosulfonic membranes are quite dependant of a high hydratation9 and, consequently are limited in the filed of use8,10 : low temperature (< 90°C) and high relative humidity (HR > 80%). Hence, increasing the temperature and decreasing the relative humidity are real challenges for the development of protonic PEMFCs. Our recent objectives were to find out new fluorinated membranes bearing either nitrogenous heterocycles such as (benz)imidazoles (more basic than water but not linked to the relative humidity). or phosphonic acids (though less acidic than sulfonic ones but more dependant of the relative humidity11). The key strategy to enable a suitable compromise for both a high amount fluoromonomers and of functions that insure the conductivity is to carry out an alternating copolymerization of chlorotrifluoroethylene and a monomer which bears such a function. Hence, the radical copolymerization du CTFE with 2-chloroethyl vinyl ether (CEVE) to obtain poly(CTFE-alt-CEVE) copolymers was first achieved for further chemical modifications to synthesize original copolymers that containing (benz)imidazole12 or phosphonic acid.