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851.
Sylvain Chambon Agnès Rivaton Jean-Luc Gardette Muriel Firon 《Polymer Degradation and Stability》2011,96(6):1149-1158
This paper reports a study of the photo- and thermo-degradation of poly(p-phenylene-vinylene)-type (PPVs) materials, including a five-ring n-octyloxy substituted phenylene-vinylene oligomer (Ooct-OPV5) and poly(p-phenylene-vinylene) (PPV). The modifications in the chemical structure of the thin films submitted to UV-visible light irradiation and thermal oxidation were analysed with infrared spectroscopy, and the oxidation products were identified by derivatisation reactions. Results showed that the photochemical and thermal behaviour of the Ooct-OPV5 oligomer was similar to that of MDMO-PPV (poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene), which is a polymer used in organic solar cells. Additionally, the identification of the products resulting from the oxidation of the vinylene bonds was simpler in Ooct-OPV5 and PPV compared to MDMO-PPV In contrast, the oxidation mechanisms of PPV, which has no ether substituent, and MDMO-PPV are not identical; the disappearance of the double bonds in PPV does not involve the formation of aromatic ketones. It was also shown that the absence of ether substituents does not decrease the rate of photo-oxidation of PPV compared to MDMO-PPV. Finally, as the same mechanisms proposed for Ooct-OPV5 and PPV occur under both photo- and thermo-oxidative conditions of ageing, this confirms that singlet oxygen does not play a decisive role in the photo-oxidation of PPVs. 相似文献
852.
Staub A Zurlino D Rudaz S Veuthey JL Guillarme D 《Journal of chromatography. A》2011,1218(49):8903-8914
The objective of this study was to evaluate the potential of sub-2 μm totally porous particles and sub-3 μm shell particles for peptide and protein analysis. Specific analytical strategies must be developed for these biomolecules as their importance in the pharmaceutical industry increases and as their structural complexity involves some issues when classical LC conditions are employed. Attention was paid on comparing these different columns in various LC conditions (different temperatures, gradient times, and mobile phase flow rates). The comparison of the different supports was assessed considering columns characteristics (quality of packing, silanol activity, pore size, totally porous or shell particles). In this article, peptides were first analyzed with both column technologies. Similar results to those achieved with low molecular weight compounds were obtained (peak capacity >100 for tgrad around 3 min and columns dimensions of 2.1 mm id × 50 mm), but specific conditions were required (elevated temperature and the use of a volatile ion-pairing reagent, namely TFA). For peptide analysis following tryptic digestion, the goal was to improve peak capacity and resolution because of the large number of generated peptides. For this purpose, longer columns packed with porous sub-2 μm or shell sub-3 μm particles (i.e., 150 mm) and gradient times (i.e., up to 30 min) were tested. On the other hand, proteins in their intact forms have higher molecular weights (MW > 5000 Da) and a tertiary structure, thus requiring different conditions in terms of stationary phase hydrophobicity (C4vs. C18) and pore size (300 vs. 120 Å). In addition, there were issues with adsorption onto the LC system and/or the column itself. This study showed that proteins with MWs lower than 40,000 Da required chromatographic conditions close to those employed for peptide analysis. For larger proteins, a C4 300 Å stationary phase gave the best results, confirming theoretical predictions. 相似文献
853.
Ramona Pristavita Ranjan Roy Blain Moran Jean-Luc Meunier Dimitrios Berk 《Plasma Chemistry and Plasma Processing》2011,31(6):839-850
Carbon black nanopowders were produced using two thermal plasma processes based on DC, respectively ICP plasma torches. Although
the produced particles were in the nanometer size range, the values obtained for the surface area of the particles using a
Brunauer Emmett Teller technique were very small. This indicated the presence of contaminants in the experimental powders,
as confirmed by Raman spectroscopy and Thermogravimetric Analysis. A thermal treatment process was developed in order to extract
these volatile compounds, which were then identified using a Gas Chromatography—Mass Spectrometry method. The experimental
powders were analyzed using Scanning and Transmission Electron Microscopy, X-Ray Diffraction and Raman Spectroscopy before
and after the thermal treatment in order to determine the effect of the heat treatment on the powder structural properties. 相似文献
854.
Polycyclic structures fused at a central carbon are of great interest due to their appealing conformational features and their structural implications in biological systems. Although progress in the development of synthetic methodologies towards such structures has been impressive, the stereoselective construction of such quaternary stereocentres remains a significant challenge in the total synthesis of natural products. This review highlights the progress in the formation of 1-oxaspiro[4.n]alkan-2-ones (2≤n≤7) with concomitant formation of the quaternary spiro centre. 相似文献
855.
François Constantin Françoise Fenouillot Jean-Luc Guillaume Raymond Koenig Jean-Pierre Pascault 《Macromolecular Symposia》2003,198(1):335-344
Properties of thermoplastic modified epoxy network have been studied. The particularity of this work is the use of new thermoplastic epoxies whose structure is close to the final matrix. Blends of thermoset epoxy (Diglycidyl Ether of Bisphenol A/4-4′ methylenebis [3-chloro 2,6-diethylaniline]) with a thermoplastic content from 5 to 40%w have been realised. Initial miscibility in the thermoset precursors shows an UCST behaviour with a maximal value near 130°C for a thermoplastic content of 10%. Due to the presence of tertiary amine and pendant hydroxyl groups on the thermoplastic backbone, epoxy amine reactions are faster than for the neat system but the thermoplastic seems not to have reacted with the thermoset network. The final blends are transparent but toughening increase is rather low. 相似文献
856.
Hélène Angellier Jean-Luc Putaux Sonia Molina-Boisseau Danielle Dupeyre Alain Dufresne 《Macromolecular Symposia》2005,221(1):95-104
Aqueous suspensions of nanocrystals can be obtained by acid hydrolysis of native waxy maize starch granules. The disruption of waxy maize starch granules by 2.2N HCl hydrolysis has been followed by scanning and transmission electron microscopy and laser granulometry. The mechanical properties of composite materials made of poly(styrene-co-butyl acrylate) filled with starch nanocrystals were characterized by dynamic mechanical analysis. These nanocrystals appeared to be an interesting reinforcing phase in a thermoplastic matrix. 相似文献
857.
Vincent Parent Jean-Luc Brdas Philippe Dubois Nathalie Ropson Robert Jrme 《Macromolecular theory and simulations》1996,5(3):525-546
We present a theoretical study on aluminium triisopropoxide (Al(OiPr)3) using both empirical (Molecular Mechanics, MM, with Dreiding II force field) and quantum-chemical (Austin Model 1, AM1, semiempirical Hartree-Fock) techniques. We determine the most stable geometries for both the tetramer and trimer of aluminium triisopropoxide as well as the thermodynamic characteristics of the equilibrium existing between these two aggregated structures. The theoretical results are compared to experimental data from X-ray diffraction and 27A1 NMR measurements. For the tetramer, it appears that the optimal equilibrium geometries are in good agreement with the experimental X-ray diffraction geometry; another geometry is also obtained with both theoretical approaches, which is slightly less stable but of higher symmetry. On the basis of the most stable configurations for the tetramer and trimer aggregates, the variation of free enthalpy (ΔG) between the two aggregated structures has been estimated. The evolution of the theoretical ΔG values indicates a displacement of equilibrium towards the trimer species with temperature, in good agreement with experimental 1H and 27A1 NMR data. Moreover, the AM1 heats of formation show a gain of 33.9 kcal/mol due to the aggregation of four A1(OiPr)3 instead of three, and thus a better stability of the tetramer. The molecular geometries being well described by the theoretical methods used in this study, we also present a model for the ring-opening polymerization complexes of ε-caprolactone and lactides. 相似文献
858.
The objective of this paper is to demonstrate the use of Reduced-Order Models (ROM) based on Proper Orthogonal Decomposition (POD) to stabilize by vertical oscillations the flow over a circular cylinder at a Reynolds number equal to 60. Since in Fluid-Structure Interaction, the POD algorithm cannot be applied directly, we then implement the fictitious domain method of [1] where the solid domain is treated as a fluid undergoing an additional constraint. The POD-ROM is classically obtained by projecting the Navier-Stokes equations on a small number of POD modes. The cylinder movement is then enforced in the POD-ROM through the introduction of Lagrange multipliers. A Linear Quadratic Regulator framework is used to determine the optimal control law, in our case the vertical velocity of the cylinder, such that the flow is stabilized. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
859.
Xavier Crispin Christophe Bureau Victor Geskin Roberto Lazzaroni Jean-Luc Bredas 《ChemInform》1999,30(13):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
860.
: In an attempt to obtain a semiconducting poly(paraphenylene) PPP we have looked at the effect of ion implantion on this conjugated polymer (Ref. 1). The properties of the material may be varied according to the implantation parameters (Ref. 2) and the electrical conductivity after ion implantation of PPP remains almost constant for a long period of time. 相似文献