New semi-IPN PEMFC membranes composed ofcrosslinked fluorinated copolymer bearing triazolegroups and sPEEK for operation at low relativehumidity
Résumé
The synthesis, processing, crosslinking, and characterization of original proton conductingmembranes are presented. First, fluorinated terpolymers were obtained from the radicalterpolymerization of chlorotrifluoroethylene (CTFE), 2-chloroethyl vinyl ether (CEVE) andglycerine carbonate vinyl ether (GCVE) followed by two chemical modifications intopoly(IEVE-alt-CTFE)x-g-1H-1,2,4-triazole-3-thiol-co-(GCVE-alt-CTFE)y terpolymer that beardangling cyclocarbonate and triazole functions (where IEVE stands for 2-iodoethyl vinylether). The successful grafting (overall yields >80%) of these terpolymers was monitored by1H and 19F NMR spectroscopy and by thermal analyses (DSC and TGA) and did not shownany opening of the cyclocarbonate ring. Such fluorofunctional terpolymers were involvedin the preparation of blend membranes with sulfonated PEEK (sPEEK), followed by thecrosslinking in the presence of two telechelic diamines of different chain lengths viacyclocarbonate/amine reaction. The characterizations of these resulting membranes(thickness ¼ 35e50 mm) in term of thermal stability (>200 C under air), water uptake (aslow as <20%), conductivity, and mechanical properties (strainestress relationships and bydynamical mechanical analysis) were comprehensively investigated to understand theinfluence of the nature of the diamines, the crosslinking, and the presence of azole groupon membrane microstructure. Proton conductivities of crosslinked blend membranescomprising such fluorinated polymer components functionalized with triazole at 140 Cand at low relative humidity (<25%) reached 4.3 mS cm1 for a blend membrane containing60%-wt of s-PEEK and 40%-wt of poly(CTFE-alt-IEVE)82%-g-1H-1,2,4-triazole-3-thiol86%-co-(CTFE-alt-GCVE)18% terpolymer. They displayed glass transition temperatures, Youngmodulus and tensile strengths up to 223 C, 4 MPa and 6%, respectively.