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 phaseseparated 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.

A series of organic‐inorganic hybrid particles were synthesized by a self‐assembled layer of different initiators, immobilized on silica particles and used for controlled radical polymerization. We use three different initiator systems for atom‐transfer radical polymerization (ATRP), unimolecular nitroxide mediated polymerization (NMP), and bimolecular NMP, for the development of the hybrid inorganic/organic particles. After preliminary qualitative characterization by X‐ray spectroscopy (XPS) and Fourier‐transformed infrared (FT‐IR) measurements, the hybrid nanoparticles were studied by thermogravimetric analysis (TGA) to determine and discuss the initiator graft density in terms of steric hindrance.The coupling agents employed for the various approaches used here: a) NMP1‐bimolecular system, b) NMP2‐unimolecular system, and c) ATRP.magnified imageThe coupling agents employed for the various approaches used here: a) NMP1‐bimolecular system, b) NMP2‐unimolecular system, and c) ATRP.

AFM-based single molecule force spectroscopy has been applied to study the detachment of poly-(acrylic acid) (PAA) chains preadsorbed onto a silicon nitride tip surface at varied pH. In particular, monolayers of end-grafted chains prepared by nitroxide-mediated polymerization initiated from silica substrates were brought into close contact with the silicon nitride tip of an AFM. The detachment of PAA chains from the tip surface is reflected by a set of constant-force plateaus in the AFM force spectra. From those, comprehensive information about the molecular length distribution of surface-grafted polymers, about their conformation, and about their interaction with the tip as a function of pH is deduced. At neutral pH, the plateau-length distribution well reproduces the molecular weight distribution of the grafted polymers as obtained by GPC. At high pH, increasing electrostatic repulsion between PAA and the tip surface reduces the strength of adsorption, which is manifested in a decrease of average plateau lengths and measured detachment forces. At low pH, complex force spectra and a bimodal distribution of apparent molecular lengths are obtained, reflecting the poor solubility of protonated PAA chains in water as well as polymer-substrate interactions.

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