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171.
A. Grüger P. Gotthardt M. Pnitsch H. G. Brion R. Kirchheim 《Journal of Polymer Science.Polymer Physics》1998,36(3):483-494
Pressure-composition isotherms were determined at 20°C for CO2 in Kapton and various substituted polycarbonates and for H2O, Ar, N2, CH4, and acetone in bisphenol-A-polycarbonate. The isotherms are described by two parameters an average free energy of sorption and a width of a Gaussian distribution of free sorption energies. Within the framework of a recent model these parameters can be calculated assuming an elastic distortion of the polymer caused by the incorporation of solute atoms in preexisting holes. By comparing experimental values with predictions of the model the experimental width of the free energy distribution is only 30% smaller than the theoretical one. Functional relationships are obeyed between the sorption parameters on the one hand and glass transition temperature, average hole volume, and molecular volume of the solute on the other hand. Deviations occur for larger molecules like acetone and ethylene which are attributed to a viscoelastic distortion of the polymer. Comparing free energies of solution for the rubbery and glassy state of the polymer reveals more negative values for the glassy polymers despite their extra elastic distortion energy. This discrepancy is overcome by taking into account that the occupied volume has to be re-formed in the case of the rubbery or liquid polymer. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 483–494, 1998 相似文献
172.
173.
Stereoretentive Copper‐Catalyzed Directed Thioglycosylation of C(sp2)−H Bonds of Benzamides 下载免费PDF全文
Amélie Chabrier Dr. Alexandre Bruneau Sara Benmahdjoub Dr. Belkacem Benmerad Dr. Sabrina Belaid Jean‐Daniel Brion Dr. Mouâd Alami Dr. Samir Messaoudi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):15006-15010
An efficient thioglycosylation of C(sp2)?H bonds with thiosugars has been established for the first time. Using only Cu(OAc)2?H2O as a catalyst and Ag2CO3 as an additive in DMSO, the protocol proved to have broad scope, and a variety of complex thioglycosides have been prepared in good yields with exclusive β‐selectivity. 相似文献
174.
175.
We obtain residue formulae for certain functions of several variables. As an application, we obtain closed formulae for vector partition functions and for their continuous analogs. They imply an Euler-MacLaurin summation formula for vector partition functions, and for rational convex polytopes as well: we express the sum of values of a polynomial function at all lattice points of a rational convex polytope in terms of the variation of the integral of the function over the deformed polytope.
176.
Nathalie LHermite Jean-Franois Peyrat Moud Alami Jean-Daniel Brion 《Tetrahedron letters》2005,46(52):8987-8991
A rapid convergent synthesis of first- and second-generation halogenated linear poly(arylpropargyl ether) branches 7 and 10 is described. The key step of the sequence studied involves a selective Sonogashira–Linstrumelle (S–L) cross-coupling reaction of aryl iodides with alkynes bearing an sp2-carbon–iodine bond. Application to the synthesis of functionalized first-generation poly(arylpropargylether) stars having a benzene-1,3,5-tricarboxylic acid core has been realized. 相似文献
177.
We show that any normal algebraic monoid is an extension of an abelian variety by a normal affine algebraic monoid. This extends
(and builds on) Chevalley's structure theorem for algebraic groups. 相似文献
178.
Let G be a connected semisimple algebraic group, B a Borel subgroup, T a maximal torus in B with Weyl group W, and Q a subgroup containing B. For , let denote the Schubert variety . For such that , one knows that ByQ / Q admits a T-stable transversal in , which we denote by . We prove that, under certain hypotheses, is isomorphic to the orbit closure of a highest weight vector in a certain Weyl module. We also obtain a generalisation of
this result under slightly weaker hypotheses. Further, we prove that our hypotheses are satisfied when Q is a maximal parabolic subgroup corresponding to a minuscule or cominuscule fundamental weight, and is an irreducible component of the boundary of (that is, the complement of the open orbit of the stabiliser in G of ). As a consequence, we describe the singularity of along ByQ / Q and obtain that the boundary of equals its singular locus.
Received October 9, 1997; in final form February 19, 1998 相似文献
179.
El Dib G Chakir A Roth E Brion J Daumont D 《The journal of physical chemistry. A》2006,110(25):7848-7857
The ultraviolet absorption spectrum of benzylperoxy radical and the kinetics of the reactions 2C(6)H(5)CH(2)O(2) --> products (I) and C(6)H(5)CH(2)O(2) + HO(2) --> products (II) are studied. Experiments are carried out using the laser photolysis technique with time-resolved UV-visible absorption spectroscopy over the temperature range 298-353 K and the pressure range 50-200 Torr. The UV spectrum is determined relative to the known cross section of the ethylperoxy radical C(2)H(5)O(2) at 250 nm. Using factor analysis, the spectrum obtained is refined and the concentrations of the main absorbing species are extracted. The kinetic parameters are determined by analyzing and simulating the temporal profiles of the species concentrations and the experimental optical densities in the spectral region 220-280 nm. These are obtained using the recent UV spectra of the absorbing species existing in our mechanism. The Arrhenius expressions for reactions I and II are (cm(3).molecule(-1).s(-1)) k(I) = 2.50 x 10(-14)e(1562/)(T) and k(II) = 5.70 x 10(-14)e(1649/)(T). Our results are discussed and compared to literature data. 相似文献
180.
[STRUCTURE: SEE TEXT] The first platinum-catalyzed selective silylation of aryl halides including aryl iodides and bromides having an electron-withdrawing group is described. The reaction takes place rapidly in NMP with triethylsilane as a silicon source and sodium acetate to provide functionalized aryltriethylsilanes in moderate to good yields. Heteroaromatic halides also were found to be readily silylated with triethylsilane. The procedure is chemoselective and tolerates a wide variety of functional groups. 相似文献