Novel UV‐induced photografting process for preparing poly(tetrafluoroethylene)‐based proton‐conducting membranes

A novel process comprising the UV‐induced photografting of styrene into poly(tetrafluoroethylene) (PTFE) films and subsequent sulfonation has been developed for preparing proton‐conducting membranes. Although under UV irradiation the initial radicals were mainly generated on the surface of the PTFE films by the action of photosensitizers such as xanthone and benzoyl peroxide, the graft chains were readily propagated into the PTFE films. The sulfonation of the grafted films was performed in a chlorosulfonic acid solution. Fourier transform infrared and scanning electron microscopy were used to characterize the grafted and sulfonated membranes. With a view to use in fuel cells, the proton conductivity, water uptake, and mechanical properties of the prepared membranes were measured. Even through the degree of grafting was lower than 10%, the proton conductivity in the thickness direction of the newly prepared membranes could reach a value similar to that of a Nafion membrane. In comparison with γ‐ray radiation grafting, UV‐induced photografting is very simple and safe and is less damaging to the membranes because significant degradation of the PTFE main chains can be avoided. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2624–2637, 2007     

A characterization of certain irreducible symplectic 4-folds

 We give a characterization of irreducible symplectic fourfolds which are given as Hilbert scheme of points on a K3 surface. Received: 26 June 2002 / Revised version: 9 September 2002 Published online: 14 February 2003 Mathematics Subject Classification (2000): Primary 14J32, Secondary 32Q20     

Development of direct fluorination technology for application to materials for lithium battery

Direct fluorination of 1,3-dioxolan-2-one with elemental fluorine was successfully carried out to provide 4-fluoro-1,3-dioxolan-2-one, which was expected as an additive for lithium ion secondary battery. 4-Fluoro-1,3-dioxolan-2-one was also further fluorinated with elemental fluorine to give three isomers of difluoro derivatives by the same methodology. Another topic is the preparation of trifluoromethanesulfonyl fluoride, an intermediate of lithium battery electrolyte, by the reaction of methanesulfonyl fluoride with elemental fluorine. The use of perfluoro-2-methylpentane as a solvent gave satisfactory selectivity of trifluoromethanesulfonyl fluoride.     

Wiener's test for space-time random walks and its applications

This paper establishes a criterion for whether a -dimensional random walk on the integer lattice visits a space-time subset infinitely often or not. It is a precise analogue of Wiener's test for regularity of a boundary point with respect to the classical Dirichlet problem. The test obtained is applied to strengthen the harder half of Kolmogorov's test for the random walk.

     

Pd/C-Et3N-mediated catalytic hydrodechlorination of aromatic chlorides under mild conditions

A mild and efficient one-pot procedure for the hydrodechlorination of aromatic chlorides using a Pd/C-Et₃N system was developed. A variety of aromatic chlorides could be dechlorinated at room temperature and under ambient hydrogen pressure. Et₃N activates the catalysis and is likely to work as a single electron donor in this system.     

Accurate mass measurement of low molecular weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We report the application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the accurate measurement of mass of low molecular weight compounds (smaller than 1500 Da), a linear peptide, two types of cyclic depsipeptides, a polyhydroxy-macrocyclic lactone, and two prenylated flavonoids, with delayed extraction in the reflector mode. The performance of the MALDI-TOF instrument was less than those of fast atom bombardment and Fourier-transform ion cyclotron resonance mass spectrometry instruments and insufficient to give acceptable accuracy for literature reporting. Nevertheless, when combined with NMR spectrometry and/or amino acid analysis to give information on the numbers of carbon atoms and index of hydrogen deficiency, MALDI was useful for determination of the elemental composition of the low molecular weight compounds available in small quantities.     

Oxidative cyclization of morusin

Oxidative cyclization of morusin (I) by using one-electron transfer oxidizing agents (manganese dioxide, silver oxide) afforded morusin hydroperoxide (II). A similar reaction was carried out in the presence of 2,4,6-tri-t-butylphenol, a radical quencher, to give compounds (IV, V, VI and VII) coupled with the 2,4,6-tri-t-butylphenoxy radical. On the basis of above results, the possible mechanism of this oxidative cyclization was discussed. In addition, morusin hydroperoxide (II) was also obtained by photo-sensitized oxidation of morusin (I) in the presence of sensitizers (Rose Bengal, hematoporphyrin). To elucidate the reaction mechanism similar reactions were carried out in the presence of radical quencher (2,4,6-tri-t-butylphenol) or singlet oxygen quencher (triethylenediamine). From these results, the possible mechanism of the formation of morusin hydroperoxide (II) from morusin (I) was discussed.     

Diffusion of hydrogen in metals

The present status of our understanding of the diffusion of hydrogen in metals, both experimental and theoretical, is reviewed. Discussions are focused on the mechanism of diffusion of hydrogen isotopes H, D and T in f.c.c. and b.c.c. metals; the positive muon (μ ⁺) is referred to where appropriate. An up-to-date compilation of diffusion data as a function of temperature and isotope mass has been made, and a clear distinction in general diffusion behaviour in f.c.c. and b.c.c. metals is noted. Subsequently, the results obtained from the Gorsky effect, nuclear magnetic resonance and quasi-elastic neutron scattering that provide information on elementary jump processes are discussed.

A conceptual framework of the quantum diffusion of light interstitials in metals is given, including the recent Kondo theory that emphasizes the crucial importance of particle-conduction electron interactions in the diffusion process, especially at low temperatures. It is shown with the help of recent estimates of the tunneling matrix element that the overall feature of diffusion of hydrogen isotopes in b.c.c. metals as well as μ ⁺ in f.c.c. metals can be explained consistently within the frame presented here.

Finally, recent advances in the diffusion studies on hydrogen in b.c.c. metals are described. They include a re-analysis of quench-recovery experiments that manifested nearly athermal diffusion of H, D and T in Ta at low temperatures, and an enormous enhancement of the diffusivity under stress (superdiffusion) observed for H and D in V.     

Efficient partial hydrogenation of trichloromethyl to gem-dichloromethyl groups in platinum on carbon-catalyzed system

While gem-dichloromethyl groups can be directly synthesized by the mono-dechlorination of the corresponding trichloromethyl groups, the suppression control of the over-reduction to form chloromethyl or methyl functionalities is quite difficult. We have established the efficient and widely applicable mono-dechlorination method of the trichloromethyl groups to form the corresponding gem-dichloromethyl groups using platinum on carbon in dimethylacetamide as a specific solvent at 25 °C under a hydrogen atmosphere. The mono-dechlorination of the α,α,α-trichloromethylcarbonyl groups smoothly proceeded by the use of platinum on carbon as a catalyst in a highly chemoselective manner, while the efficient mono-dechlorination of the alkyl- and aryl-trichloromethyl groups required the combined use of Bu₃SnH.     

Rotation rate of a three-wing rotor illuminated by upward-directed focused beam in optical tweezers

The optical torque and the trapping position (focal point) in optical tweezers are analyzed for upward-directed focused laser illumination using a ray optics model, considering that laser light is incident at not only the lower surface but also the side surface of a 3-wing rotor. The viscous drag force due to the pressure and the shearing stress on all surfaces of the rotor is evaluated using computational fluid dynamics. The rotation rate is simulated in water by balancing the optical torque with the drag force, resulting in 500 rpm for an SU-8 rotor with 20 μm diameter at a laser power of 200 mW. The trapping position is estimated to be 7.6 μm in the rotor with an upward-directed laser at 200 mW via an objective lens having a numerical aperture of 1.4. Both the rotation rate and the trapping position agree well with the values obtained in the experiment.