Abstract
Proton exchange membrane fuel cells requires an electrolyte membrane that is a perfluoro sulfonated polymer marketed by Dupont under the Nafion tradename. Poly(VDF-co-HFP) copolymers grafted by amines exhibit potential properties that allow them to be suitable candidates for fuel cell applications. The crosslinking of such copolymers by an aliphatic diamine led to materials endowed with good thermal, chemical and mechanical properties. The study of grafting of poly(VDF-co-HFP) copolymers by aromatic containing-amines (aniline, benzylamine, phenylpropylamine) permitted to identify the sites of grafting of these amines, but also to investigate the kinetics of grafting and to assess the influence of temperature and the molar % of HFP in the copolymer. Finally, the influence of the spacer between aromatic ring and amino group on the kinetics of grafting showed that with more than two methylene groups, the kinetics was faster. Then, the study of the dehydrofluorination and the addition of phenylethylamine onto a fluorinated model molecule permitted to well- understand the mechanism of grafting of amines. An original amine comprising a sulfonated aromatic ring was synthesized by telomerization of sulfonated styrene with a mercapto transfer agent. After modification, this amine was grafted onto commercially available poly(VDF-co-HFP) copolymer. Properties were assessed and membranes seemed to exhibit suitable properties for electrolyte application in PEMFC, although the proton conductivity was still low compared to that of Nafion. Finally, the grafting of a sulfonated phenate onto poly(VDF-co-HFP) copolymers was carried out; it showed similar properties as amine grafted copolymers with a lower water up take, close to that of Nafion.