[en] Various benzoxazoles were synthesized and investigated by mass spectrometry. The relative stabilities of their molecular ions were used in the search for radiostable polybenzoxazoles (PBO). The three polybenzoxazoles corresponding to the three bibenzoxazoles previously investigated were irradiated by 900 keV electrons, and their aging was followed in situ by optical measurements. The most radiostable polymer corresponds to the model compound (diphenylbibenzoxazole), which is characterized by the highest degree of conjugation and by the lowest number of fragmentations in mass spectrometry. The resistance of this new polymer to electron irradiation is better than that of Teflon FEP or Kapton H

No abstract available

[en] The γ-radiolysis of 2-propanol solutions of cyclohexanone gives mainly hydrogen, acetone, pinacol, methane derived from 2-propanol, and cyclohexanol, 2-(2-cyclohexanonyl)-cyclohexanone, and 3-(2-hydroxy-2-propyl)cyclohexanone derived from cyclohexanone. The radiolytic yields of all these products were highly dependent on the initial cyclohexanone concentration. The formation of cyclic alcohols by radioreduction has been extended to various substituted cyclohexanones. Radiolytically generated solvated electrons are scavenged by cyclohexanone, leading to the corresponding radical anions. The protonation of these radical anions gives rise to cyclohexanol via the dismutation of the hydroxycyclohexyl radicals. Steady state radiolysis measurements were complemented by pulse radiolysis in dilute solution. It was established that radical-anions and hydroxylated radicals decayed according to a second order rate law. When ketone concentration was lower than 0.1 M, radiolytic yields were in agreement with the mechanism mentioned above. However, in concentrated media the large increase in G(cyclohexanol) cannot be only accounted for by the involvement of radiolytically generated solvated electrons; probably it is due to an electron transfer from the cyclohexanone enolate to cyclohexanone itself, thus generating extra amounts of cyclohexanone radical anions. (author)

[en] Small angle neutron and X-ray scattering was used to study micellization of cetyltrimethylammonium bromide (CTAB) in partially deuterated or hydrogenated formamide from the absolute values of scattered intensities. Highly charged aggregates of around 6 monomers were observed at CTAB concentrations above the cmc (2.8% wt at 60degC). These aggregates along with spherical particles (2 nm radius) containing 29 monomers were consistently observed at concentrations above 8%. These particles were considered to be micelles as they had similar structure, albeit of smaller size to those observed in water (2.7 nm, aggregation number 90). They also had a higher charge in formamide than in water (degree of ionization 0.55 in formamide and 0.14 in water). With increase in surfactant concentration, the micelles elongated, although the radius of the cylinders in the two dimensional hexagonal phase remained close to 2 nm. The importance of interactions of polar head with solvent molecules of high dipole moment and dielectric constant is discussed. The less spontaneous self-association of surfactant molecules in formamide than in water poses the problem of the definition of the cmc. (orig.)