Polysulfones grafted with poly(vinylphosphonic acid) for highly proton conducting fuel cell membranes in the hydrated and nominally dry state

Mechanically strong and flexible membranes with very high local concentrations of immobilized proton-conducting phosphonic acid have been achieved by grafting poly(vinylphosphonic acid) side chains onto polysulfones. The graft copolymers were prepared by anionic polymerization of diethyl vinylphosphonate initiated from lithiated polysulfones, followed by quantitative cleavage of the ester functions. The resulting phosphonic acid units acted like monoprotic acids to indicate a high level of intramolecular interactions, and the phase-separated nature of the copolymers was shown by dual glass transitions. Fully polymeric membranes were conveniently cast from solution and showed high proton conductivities, e.g., 5 mS/cm under nominally dry conditions at 120 °C and up to 93 mS/cm under 100% relative humidity at the same temperature. The corresponding conductivities measured for Nafion 115 under the same conditions were 0.04 and 105 mS/cm, respectively. The former membranes furthermore showed high thermal stability with decomposition temperatures exceeding 300 °C under air. Additions of 2−5 wt % of a perfluorosulfonic acid polymer to the phosphonated membranes were found to reduce the water uptake significantly, thus improving the mechanical properties. The conductivity of these fully polymeric doped membranes was generally observed to be enhanced, or at least to remain at the same level, under both humidified and nominally dry conditions. The findings of this study demonstrate that phosphonated membranes with a proper macromolecular design may potentially show some important advantages in relation to the more commonly studied sulfonated membranes in fuel cell applications

Poly(arylene ether sulfone)s with phosphonic acid and bis(phosphonic acid) on short alkyl side chains for proton-exchange membranes

Poly(arylene ether sulfone)s have been functionalised with alkyl side chains carrying phosphonic acid and bis(phosphonic acid) in order to investigate their properties as membrane materials. The phosphonated and bisphosphonated polymers were synthesised via lithiation of poly(arylene ether sulfone)s, followed by reactions with triethyl 3-phosphonopropionate and tetraisopropyl vinylidenediphosphonate, respectively. Flexible and mechanically tough acidic membranes were cast from solution after hydrolysis of the ester groups. The significantly higher acidity and acid concentrations of the membranes containing the tetraprotic bis(phosphonic acid) led to higher conductivities in comparison to the membranes containing the diprotic phosphonic acid. Membranes containing 1.7 mmol of bis(phosphonic acid)/g dry polymer absorbed 28 wt% water when immersed at room temperature, and a conductivity of 25 mS/cm was measured at 120 °C. Moreover, the bisphosphonated membranes did not decompose at temperatures of up to 240 °C under air. The study also showed that high degrees of hydrolysis of the bisphosphonate units were crucial in order to reach the high proton conductivity and thermal stability necessary for fuel cell applications

Formation de brosses d'élastomères sur surfaces siliciées (Utilisation de la Polymérisation Radicalaire Contrôlée par l'intermédiaire de nitroxydes.)

L'objectif de ce travail consistait à former des brosses de polyacrylate via la Polymérisation Radicalaire Contrôlée par l'intermédiaire de nitroxyde. Dans le cas des particules de silice, nous avons identifié les caractéristiques propres à la PRC en surface et démontrer l'efficacité de cet outil vis-à-vis de la formation de couches de polyacrylates sur des substrats poreux. Par ailleurs, une comparaison directe des chaînes greffées à celles formées en solution met en évidence quelques différences ; la cinétique de la polymérisation à partir de la surface s'avère plus lente favorisant ainsi un meilleur contrôle de la polymérisation. L'application aux wafers de silicium nous a permis de confirmer l'efficacité de la méthode utilisée par l'obtention d'une densité de greffage élevée. De plus, les résultats ont démontré le caractère contrôlé/vivant de la polymérisation à partir de la surface permettant ainsi la formation de brosses de polymères et de copolymères à blocs.The main objective consisted of generating elastomer brushes via Controlled Radical Polymerization on silica substrates. In the case of the silica particles, we identified the specific characteristics of the CRP at the surface and showed the effectiveness of this tool in forming polyacrylate thin layers on porous substrates. In addition, a direct comparison of the polymer populations (grafted and free polymers) highlighted some differences. Indeed, the kinetic of polymerization starting from the surface were slower than in the volume, allowing a better control of the former. With regard to silicon wafers, the application of this system enabled us to obtainh high grafting density. Moreover, the results showed a living/controlled character of the radical polymerization starting from the surface. This type of radical polymerization thus represents an effective tool for the formation elastomers brushes.PAU-BU Sciences (644452103) / SudocSudocFranceF

Synthesis of HCN-like poly(methyl methacrylate)/polystyrene/silica colloidal molecules

This communication reports about the feasibility of preparing triphasic clusters made of the combination of silica, polystyrene and poly(methyl methacrylate) nanoparticles. Silica-polystyrene dimers were used as seeds in methyl methacrylate emulsion polymerisation. The competition between silica surface nucleation and swelling/phase separation phenomena from the polystyrene nodule is discussed

Efficient Synthesis of Snowman- and Dumbbell-like Silica/Polymer Anisotropic Heterodimers through Emulsion Polymerization Using a Surface-Anchored Cationic Initiator

We report a novel original synthetic route to hybrid dissymmetrical snowman- and dumbbell-like silica/polymer colloidal particles through emulsion polymerization of methyl methacrylate (MMA) or styrene using a bicationic initiator previously anchored on the silica surface. Anisotropic particles with a polymer nodule attached to a single silica sphere were successfully obtained in high yield in the presence of a mixture of nonionic and anionic surfactants under optimized initiator concentration conditions. Both nonionic surfactant and cationic initiator were key ingredients in controlling particle morphology as evidenced by transmission electron microscopy. By optimizing the silica content and the surfactant composition, latexes with a latex-to-silica seed number ratio (NLatex/NSilica) close to 1 were produced using either MMA or styrene as monomers. Their shapes evolved from snowman-like and reverse snowman-like at low and high conversions to dumbbell-like for intermediate conversions. The evolution of particle morphology with time provided insights into the mechanism of composite particles formation

Temperature Response of Rhodamine B-Doped Latex Particles. From Solution to Single Particles

We thank Vincent Joly and Xavier Dagany for the development of data acquisition for fluorescence and Laure Cohendet and Mathilde Ghafar (MSc student) for their contribution to this work. Jacques Maurelli and Christian Clavier are acknowledged for their invaluable technical assistance.International audienceNanoparticle-based temperature imaging is an emerging field of advanced applications. Herein, the sensitivity of the fluorescence of rhodamine B-doped latex nanoparticles toward temperature is described. Submicrometer size latex particles were prepared by a surfactant-free emulsion polymerization method that allowed a simple and inexpensive way to incorporate rhodamine B into the nanoparticles. Also, rhodamine B-coated latex nanoparticles dispersed in water were prepared in order to address the effect of the dye location in the nanoparticles on their temperature dependence. A better linearity of the temperature dependence emission of the rhodamine B-embedded latex particles, as compared to that of free rhodamine B dyes or rhodamine B-coated latex particles, is observed. Temperature-dependent fluorescence measurements by fluorescent confocal microscopy on individual rhodamine B-embedded latex particles were found similar to those obtained for fluorescent latex nanoparticles in solution, indicating that these nanoparticles could be good candidates to probe thermal processes as nanothermometers