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Experimental evidences regarding the sulfonation of polyoxadiazole and oxadiazoletriazole copolymers during the preparation are given. The structures of the polymers were qualitatively and quantitatively characterized by elemental analysis, 1 H-NMR, and FTIR.Polymers with high molecular weights (up to 470,000 g/mol) exhibiting highly oxidative stability are obtained allowing the casting of mechanically stable membranes with high storage modulus (about 4 GPa at 100°C) and high proton conductivity values (order of magnitude of 10 -2 S cm -1 at 80°C).

New functionalized particles were prepared by attaching sulfonated aromatic bishydroxy compounds onto fumed silica surface. First, a bromophenyl group was introduced onto the silica surface by reaction of bromophenyltrimethoxysilane with fumed silica. Then, sulfonated bishydroxy aromatic compounds were chemically attached to the silica surface by nucleophilic substitution reactions. The structure of the modified silica was characterized by elemental analysis: 13 C-NMR, 29 Si-NMR, and FTIR. Afterward, novel inorganic-organic electrolyte composite membranes based on sulfonated poly(ether ether ketone) have been developed using the sulfonated aromatic bishydroxy compounds chemically attached onto the fumed silica surface. The composite membrane prepared using silica with sulfonated hydroxytelechelic, containing 1,3,4-oxadiazole units, has higher proton conductivity values in all range of temperatures (40-140 8C) than the membrane containing only the plain electrolyte polymer, while the methanol permeability determined by pervaporation experiment was unchanged. A proton conductivity up to 59 mS cm À1 at 140 8C was obtained. The combination of these effects may lead to significant improvement in fuel cells (fed with hydrogen or methanol) at temperatures above 100 8C. Scheme 1. Monomers and telechelic used in the functionalization.Scheme 2. Functionalized silica surface.

Novel nanocomposite membranes were prepared with sulfonated polyoxadiazole and different amounts of sulfonated dense and mesoporous (MCM-41) silica particles. It has been shown that particle size and functionality of sulfonated silica particles play an important role when they are used as fillers for the development of polymer

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For the first time a fluorinated polyoxadiazole doped with phosphoric acid as a proton-conducting membrane for operation at temperatures above 100 °C and low humidities for fuel cells has been reported. Fluorinated polyoxadiazole with remarkable chemical stability was synthesized. No changes in the molecular weight (about 200,000 g mol-1) can be observed when the polymer is exposed for 19 days to mixtures of sulphuric acid and oleum. Protonated membranes with low doping level (0.34 mol of phosphoric acid per polyoxadiazole unit, 11.6 wt.% H 3 PO 4) had proton conductivity at 120°C and RH=100% in the order of magnitude of 10-2 S cm-1. When experiments are conducted at lower external humidity, proton conductivity values drop an order of magnitude. However still a high value of proton conductivity (6 x 10-3 S cm-1) was obtained at 150°C and with relative humidity of 1%. In an effort to increase polymer doping, nanocomposite with sulfonated silica containing oligomeric fluorinated-based oxadiazole segments has also been prepared. With the addition of functionalized silica not only doping level but also water uptake increased. For the nanocomposite membranes prepared with the functionalized silica higher proton conductivity in all range of temperature up to 120°C and RH=100% (in the order of magnitude of 10-3 S cm-1) was observed when compared to the plain membrane (in the order of magnitude of 10-5 S cm-1).