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831.
Microcapsules containing healing agents have been used to develop the self-healing polymeric composites. These microcapsules
must possess special properties such as appropriate strength and stability in surrounding medium. A new series of microcapsules
containing dicyclopentadiene (DCPD) with melamine–formaldehyde (MF) resin as shell material were synthesized by in situ polymerization
technology. These microcapsules may satisfy the requirements for self-healing polymeric composites. The chemical structure
of microcapsule was identified by using Fourier transform infrared (FTIR) spectrometer. The morphology of microcapsule was
observed by using optical microscope (OM) and scanning electron microscope. Size distribution and mean diameter of microcapsules
were determined with OM. The thermal properties of microcapsules were investigated by using thermogravimetric analysis and
differential scanning calorimetry. Additionally, the self-healing efficiency was evaluated. The results indicate that the
poly(melamine–formaldehyde) (PMF) microcapsules containing DCPD have been synthesized successfully, and their mean diameters
fall in the range of 65.2∼202.0 μm when the adjusting agitation rate varies from 150 to 500 rpm. Increasing the surfactant
concentration can decrease the diameters of microcapsules. The prepared microcapsules are thermally stable up to 69 °C. The
PMF microcapsules containing DCPD can be applied to polymeric composites to fabricate the self-healing composites. 相似文献
832.
Xu-Chun Wang Jian-Feng Li He-Ping Chen Jie-Ying Wu Hong-Ping Zhou Jia-Xiang Yang Bao-Kang Jin Yu-Peng Tian 《Transition Metal Chemistry》2007,32(5):551-557
The novel compound, 3-(E)-ferrocenyl-vinyl-N-hexylcarbazole (FVHC) was first synthesized and fully characterized by elemental analysis, IR, 1H-NMR, single-crystal X-ray diffraction, ultraviolet (UV) absorption, cyclic voltammograms (CV) and optical limiting (OL)
measurements. The result of single crystal X-ray diffraction for the compound reveals that the ferrocenyl and carbazole groups
are approximately coplanar, and bridged by double-bond with E configuration, showing that there is a well-delocalized π-electron
system in the molecule. The electrochemical investigation indicated that the electron in the FVHC may partially be delocalized
over the π-conjugated system and CT process in functionalized carbazole systems. Besides, the compound exhibited strong UV
absorption and large optical limiting effect, indicating promising potential applications as useful OL materials. 相似文献
833.
Carbon nanotube array-based biosensor 总被引:8,自引:0,他引:8
Aligned multi-wall carbon nanotubes (MWNT) grown on platinum substrate are used for the development of an amperometric biosensor. The opening and functionalization by oxidation of the nanotube array allows for the efficient immobilization of the model enzyme, glucose oxidase. The carboxylated open-ends of nanotubes are used for the immobilization of the enzymes, while the platinum substrate provides the direct transduction platform for signal monitoring. It is also shown that carbon nanotubes can play a dual role, both as immobilization matrices and as mediators, allowing for the development of a third generation of biosensor systems, with good overall analytical characteristics. 相似文献
834.
Elke Barsties Stefan Schaible Marc-Heinrich Prosenc Ursula Rief Werner Rll Oliver Weyand Birgit Dorer Hans-Herbert Brintzinger 《Journal of organometallic chemistry》1996,520(1-2):63-68
Bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (2-(CH3)2N-C9H6)2ZrCl2, and dimethylsilyl-bridged bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (CH3)2Si(2-(CH3)2N-C9H5)2ZrCl2, were prepared by reaction of the corresponding ligand lithium salts with ZrCl4 in toluene. Diffractometric structure determinations reveal C2-symmetric complex geometries for both complexes. An increased electron density at the Zr center of the dimethylamino-substituted complexes is indicated by reduction potentials which are 0.3–0.4 V more negative than those of their unsubstituted analogs. When activated with methyl aluminoxane in toluene solution, (CH3)2Si(2-(CH3)2N-C9H5)2ZrCl2 catalyzes the polymerization of propene to polymers with a microstructure comparable with that of polymers produced with other Me2Si-bridged bis(indenyl)ZrCl2 complexes, but with a substantially increased fraction of i-propyl end groups derived from alkyl exchange between Zr-polymer and Al---Me species. 相似文献
835.
Pyrolytic process has a promising potential for the environmentally friendly upgrading of lignocellulosic and plastic waste.
Thermogravimetry and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) were used to get information about the reactive
decomposition of PCL in binary mixtures with microcrystalline cellulose (MC) or sisal fibres (SF). Preliminary thermogravimetric
investigation showed that biomass is thermally degraded at lower temperatures than PCL and this process has a predominant
influence on the thermal behaviour of the mixtures. Discrepancies between the experimental and predicted TG/DTG profiles were
considered as a measurement of the extent of interactions occurring on co-pyrolysis. It was found that reactivity of PCL was
slightly increased in PCL-SF binary mixtures. Evolution of acidic products from cellulose and hemicelluloses decomposition
may promote PCL degradation in binary mixtures with SF. It seems that the co-pyrolysis process could have potential for the
environmentally friendly transformation of biocomposites. 相似文献
836.
Dieter Seebach Stefan G. Müller Urs Gysel Jürg Zimmermann 《Helvetica chimica acta》1988,71(5):1303-1318
Preparative Chromatographic Resolution of Synthetically Useful Cyclic Acetals Racemic cyclic acetals derived from aldehydes and glycine, glycolic acid, thioglycolic acid, formylacetic acid, and acetoacetic acid (oxazolidinones 4 – 13 , dioxolanones 14 , 15 , oxathiolanone 16 , dioxinones 17 – 23 ) are resolved by preparative high-pressure liquid chromatography on silica gel coated with the polymer from N-acryloylphenylalanine ethyl ester (Chiraspher®). The separation factors α range from1,1 to 2,4. Use of a Prepbar®-chromatography system allows injection of several grams at a time. The enantiomeric acetals thus obtained are fully characterized. First application to amino-acid synthesis are mentioned. 相似文献
837.
The refolding of the reduced-denatured insulin from bovine pancreas was investigated with the size exclusion chromatography (SEC). It was shown that the reduced-denatured insulin originally denatured with 7.0 mol L?1 guanidine hydrochloride (GuHCI) or 8.0 mol L?1 urea could not be refolded with a non-oxidized mobile phase. Although the oxidized and reduced glutathione (GSSG and GSH) were employed in the oxidized mobile phase, the reduced-denatured insulin still could not be renatured. However, in the presence of 2.0 mol Lt-1 urea in the oxidized mobile phase employed, the reduced-denatured insulin can be refolded with SEC, and the aggregation of denatured insulin can be diminished by urea. In addition, the disulfide exchange of reduced-denatured insulin also can be accelerated with GSSG/GSH in the oxidized mobile phase. The three disulfide bridges of insulin were formed correctly and the reduced-unfolded insulin can be renatured completely. The results were further tested with reversed-phase liquid chromatography (RPLC) and hydrophobic interaction chromatography (HIC). 相似文献
838.
This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorption capacity and
desorption capacity of a bi-solute mixture of phenol and 2-chlorophenol (2-CP). For this purpose, two different PACs; thermally
activated Norit SA4 and chemically activated Norit CA1, and their granular countertypes with similar physical characteristics,
thermally activated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better
adsorbers for phenol and 2-CP compared with chemically activated carbons, but adsorption was more reversible in the latter
case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed
in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated
the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption.
The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was
desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed
to higher energies of 2-CP adsorption. 相似文献
839.
Gröger H Hummel W Buchholz S Drauz K Nguyen TV Rollmann C Hüsken H Abokitse K 《Organic letters》2003,5(2):173-176
[reaction: see text] An enzyme-compatible biphasic reaction media for the asymmetric biocatalytic reduction of ketones with in situ cofactor regeneration has been developed. In this biphasic reaction media, which is advantageous for reactions at higher substrate concentrations, both enzymes (alcohol dehydrogenase and FDH from Candida boidinii) remain stable. The reductions with poorly water-soluble ketones were carried out at substrate concentrations of 10-200 mM, and the optically active (S)-alcohols were formed with moderate to good conversions and with up to >99% ee. 相似文献
840.
Transition structures associated with the C-C bond-formation step of the proline-catalyzed intermolecular aldol reaction
between acetone and isobutyraldehyde have been studies using density functional theory methods at the B3LYP/6-31G** computational
level. A continuum model has been selected to represent solvent effects. For this step, which is the stereocontrolling and
rate-determining step, four reactive channels corresponding to the syn and anti arrangement of the active methylene of the
enamine relative to the carboxylic acid group of l-proline and the re and si attack modes to both faces of the aldehyde carbonyl group have been analyzed. The B3LYP/6-31G**
energies are in good agreement with experiment, allowing us to explain the origin of the catalysis and stereoselectivity for
these proline-catalyzed aldol reactions.
Received: 2 April 2002 / Accepted: 18 July 2002 / Published online: 11 October 2002
Acknowledgements. This work was supported by research funds provided by the Ministerio de Educación y Cultura of the Spanish Government by
DGICYT (project PB98–1429). All the calculations were performed on a Cray–Silicon Graphics Origin 2000 of the Servicio de
Informática de la Universidad de Valencia. We are most indebted to this center for providing us with computer capabilities.
Correspondence to: L. R. Domingo e-mail: domingo@utopia.uv.es 相似文献