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951.
A numerical approach based on a recently proposed discretization technique and suitable for molecular weight calculation in emulsion polymerization is presented. The main features of this approach are (i) the direct evaluation of the complete chain length distribution without the need of predefined model distributions (as in the case of moment based methods), (ii) the large flexibility when defining the computational grid, (iii) the capability of evaluating with accuracy two integral properties of the distribution no matter how coarse the grid is and (iv) the limited computational effort required. Selected applicative examples are reported with emphasis on cases where other computational approaches give unreliable or less detailed results. 相似文献
952.
Bénédicte Lepoittevin Nadège Pantoustier Michael Alexandre Cédric Calberg Robert Jérôme Philippe Dubois 《Macromolecular Symposia》2002,183(1):95-102
In this study, layered silicate/aliphatic polyester nanohybrids were synthesized by ring-opening polymerization of ϵ-caprolactone as promoted by the so-called coordination-insertion mechanism. These nanocomposites were formed in presence of montmorillonite surface-modified by ammonium cations bearing hydroxyl group(s), such as bis(2-hydroxyethyl)methyl (hydrogenated tallow alkyl) ammonium. The lactone polymerization could be initiated by all the hydroxyl functions available at the clay surface, after activation into either tin(II) or Al(III) alkoxide active species. Hybrid nanocomposites were accordingly generated through the covalent grafting of every polyester chain onto the filler surface. Surface-grafted polycaprolactone (PCL) chains were untied and isolated by ionic exchange reaction with LiCl in THF solution and molar masses were measured by size exclusion chromatography. The PCL molar masses could be controlled and readily tuned by the content of hydroxyl groups available at the clay surface. Interestingly, initiation reaction by aluminum trialkoxide active species yielded grafted PCL chains characterized by very narrow molecular weight distribution (Mw/Mn∼1.2). These polyester-grafted layered silicate nanohybrids displayed complete exfoliation of silicate sheets as shown by X-ray diffraction (XRD) and transmission electron microscopy (TEM). 相似文献
953.
This article regroups various results on self-consistent field algorithms for computing electronic structures of molecular systems. The first part deals with the convergence properties of the “conventional” Roothaan algorithm and of the level-shifting algorithm. In the second part, a new class of algorithms is introduced, for which convergence is guaranteed by mathematical arguments. Computational performance on various test problems is reported; advantages of this new approach are demonstrated. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 82–90, 2000 相似文献
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Florence Guéguen Hélène Isnard Karsten Kossert Carole Bresson Céline Caussignac Guillaume Stadelmann Anthony Nonell Sébastien Mialle Frédéric Chartier 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(1):289-295
A methodology to purify a 166mHo solution has been developed by a combination of activity and mass concentration measurements in order to further determine the 166mHo half-life. The isobaric interference at m/q ? 166 requires Ho purification from non-natural Er with a high purification degree due to the large amount of Ho as opposed to Er. The Ho/Er separation was achieved using high-performance liquid chromatography on a semi-preparative column followed by purification on gravitational chromatography. The efficiency of the separation was evaluated after precise determination of the Er isotopic composition. The purification methodology enabled to separate Ho from Er. 相似文献
956.
Julio-César Aguilar Sylvain Bernès Paola Gómez-Tagle Richard A. Bartsch Josefina de Gyves 《Journal of chemical crystallography》2006,36(8):473-479
A new lariat ether, N,N′-di(methylenecarboxyethoxy)-4,10-diaza-2,3,11,12-dibenzo-18-crown-6, C28H38N2O8, has been characterized and tested for Pb2+ extraction in a picrate medium. The isolated complex, [(picrato-O,O′)-(N,N′-di-methylenecarboxyethoxy-4,10-diaza-2,3,11,12-dibenzo-18-crown-6)]-lead(II) picrate, [C34H40N5O15Pb]+[C6H2N3O7]−, includes a 7-coordinated Pb2+ cation complex where sidearms of the macrocycle are involved in complexation, with Pb‐O bond lengths of 2.587(4) and 2.617(4) ?. Picrate ions serve both as co-ligand and as anion for charge balance. Both free ligand and Pb2+ complex have been X-ray characterized: a = 18.4723(16), b = 24.0057(19), c = 14.4309(14) ?, β = 112.962(7)°, P21/c, for the ligand; a = 12.7591(15), b = 21.951(2), c = 16.4389(15) ?, β = 97.144(8)°, P21/n, for the complex. 相似文献
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