http://www.sigmaaldrich.com/catalog/PageNotFound.jsp?term=NAFION+MEMBRANE&interface=ALL&N=0+&mode=partialmax&lang=el®ion=GR&focus=product&mode=match%20partialmax&lang=el&region=GR&focus=product&N=0&interface=All&lang=el®ion=GR Synthesis and properties of novel proton exchange membranes based on sulfonated polyethersulfone and N-phthaloyl chitosan blends for DMFC applications