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31.
Canac Y Conejero S Donnadieu B Schoeller WW Bertrand G 《Journal of the American Chemical Society》2005,127(20):7312-7313
(Amino)(silyl)carbenes, prepared by substitution reactions at a carbene center, can survive several days at 0 degrees C. These species are not push-pull carbenes as their phosphino analogues and therefore are excellent ligands for transition-metal centers. 相似文献
32.
M. Boutin J. Lesage C. Ostiguy M. J. Bertrand 《Journal of Analytical and Applied Pyrolysis》2003,70(2):505-517
Polyurethanes are widely used in the manufacture of commercial products such as foams and paints. During combustion, these polymers can generate isocyanates, which induce adverse health effects. Polymer pyrolysis (Py) hyphenated with mass spectrometry (MS) allows the investigation of polymer thermal degradation over time/temperature. A diphenylmethanediisocyanate (MDI) polyurethane foam was analyzed with electron ionization (EI) and metastable atom bombardment (MAB) ionization at a pyrolysis temperature of 400 °C. The recently introduced MAB ionization source uses discrete energy stored in metastable atoms of gases to ionize the analytes. This characteristic allows modulation of the ionization energy by simply changing the ionization gas. The extensive fragmentation of molecular ions observed using EI 70 eV is not totally eliminated with EI 10 eV. However, only molecular ions are observed with MAB using N2 as the ionization gas. Temperature gradients were used to separate the products generated during the thermal degradation of a 1,6-hexamethylenediisocyanate (HDI) polyurethane paint. The analysis of mass spectra was facilitated owing to a selective desorption of pyrolysis products. Furthermore, changing the MAB ionization gas allows elucidation of the structure of the pyrolysis products by controlling the extent of their fragmentation. During these experiments, isocyanic acid, methyleneisocyanate, ethyleneisocyanate, propylisocyanate and butylisocyanate were detected. 相似文献
33.
A primary cleavage of aliphatic ozonides by electron-impact, implying O? O and C? C bond breaking, is described. This mode of degradation, which is not observed for aromatic ozonides, is fav oured by electron releasing substituents. For the cis and trans 4-methyl-2pentene ozonides, the ionization potentials are 8.81 and 8.86 (±0.5) eV, respectively. Two formation thresholds are observed for the [RCHO2]+ion which are interpreted in terms of different modes of ozonide cleavage. 相似文献
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Sylvain Achelle Samia Kahlal Jean-Yves Saillard Nolwenn Cabon Bertrand Caro Françoise Robin-le Guen 《Tetrahedron》2014
Thirteen novel dipolar and V-shaped chromophores with pyranylidene electron-donating part, diazine electron-withdrawing part and various π-linkers were synthesized. The extent of intramolecular charge transfer, structure-property relationships and optical properties were further investigated by UV/Vis absorption, electrochemistry, and DFT calculations. 相似文献
38.
Karla G. Gutiérrez-Cuevas Rosa Julia Rodríguez-González Bertrand Donnio Damaso Navarro-Rodríguez 《Liquid crystals》2013,40(4):534-545
In this article, we report on the synthesis and thermotropic behaviour of methacrylic polymers containing 4′-(4-alkyloxyphenyl)azobenzene mesogens attached to the backbone through n-alkyloxy spacers of 6 or 10 methylene groups. Polymerisations were carried out via free radicals using azobisisobutyronitrile (AIBN) as initiator. Chemical structures of polymers and their precursors were characterised by 1H NMR spectroscopy. Thermogravimetric analysis showed that azopolymers are thermally stable up to temperatures around 300°C. The thermotropic liquid-crystalline (LC) behaviour was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). Results indicate that all synthesised mesogens, monomers and polymers developed two or more orthogonal LC phases in wide temperature ranges. Mesogens and monomers developed nematic and smectic phases, whereas polymers exhibited only smectic phase. In polymers, the arrangement of mesogens depends on the relative length of the spacer and the terminal flexible chain; two distinct structural models were proposed based on chemical interactions and steric constrains. The trans–cis photoisomerisation of monomers and polymers in solution was also studied. High cis-isomer contents (>80%) were reached in relative short irradiation times despite the steric constrains imposed by the polymer backbone. 相似文献
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