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941.
Leesa M. Smith Michelle L. Coote 《Journal of polymer science. Part A, Polymer chemistry》2013,51(16):3351-3358
The effect of temperature and solvent on polymer tacticity in free‐radical polymerization of styrene and methyl methacrylate was studied by 13C and 1H NMR, respectively. Polystyrene shows a mild syndiotactic tendency (Pm = 0.36 ± 0.02) that is independent of temperature over a wide range (?10 to 120 °C), while poly(methyl methacrylate) shows a stronger syndiotactic tendency (Pm = 0.17 ± 0.01 at 30 °C) that decreases as temperature is increased (Pm = 0.22 ± 0.02 at 80 °C). None of the polymerization solvents studied (bulk, THF, DMF, DMSO, acetonitrile, and acetone) had a significant effect on polymer tacticity in either system. The triad fractions of both polymers showed deviations from the Bernoulli model, implying that the antepenultimate unit affects the propagation reaction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3351–3358 相似文献
942.
C. B. Ferreira M. Fernandes L. C. Rodrigues M. M. Silva M. J. Smith V. de Zea Bermudez 《Ionics》2013,19(12):1803-1809
The present study has been focused on environmentally friendly sol–gel-derived electrolytes based on a di-urethane cross-linked d-PCL(530)/siloxane network [where d represents di, PCL identifies the poly(ε-caprolactone) biopolymer, and 530 is the average molecular weight in grams per mole] doped with a wide range of concentration of lithium perchlorate and lithium bis(trifluoromethanesulfonyl)imide. Fourier Transform Infrared and Raman spectroscopies have been applied to evaluate the extent of ionic association. Characteristic bands of the PCL(530) segments, of the urethane cross-links, and of the anions have been examined to gain insight into the cation/biopolymer, cation/anion, and cation/cross-link interactions. In both electrolyte systems, “free” ions and contact ions have been identified. The addition of salt modifies the hydrogen-bonded array of the host matrix, causing the destruction/formation of the urethane/urethane aggregates. 相似文献
943.
3,4-Dihydroxy-5-alkynylcarboxylic acids, readily obtained by the addition of lithium acetylides to α-acetoxysuccinic anhydride followed by reduction and hydrolysis, undergo smooth silver(I)-catalysed 5-endo-dig cyclisations and in situ dehydration to give excellent overall yields of 5-substituted-2-furylacetic acids, including the natural metabolite plakorsin B. 相似文献
944.
945.
We perform simulations of an effective theory of SU(2) Wilson lines in three dimensions. Our action includes a kinetic term, the one-loop perturbative potential for the Wilson line, a non-perturbative “fuzzy-bag” contribution and spatial gauge fields. We determine the phase diagram of the theory and confirm that, at moderately weak coupling, the non-perturbative term leads to eigenvalue repulsion in a finite region above the deconfining phase transition. 相似文献
946.
947.
A method is derived for the numerical evaluation of the error term arising in a quadrature formula of Clenshaw-Curtis type
for functions of the form
(1-x2)l- \frac12f(x)(1-x^{2})^{\lambda - \frac{1}{2}}f(x) over the interval [−1,1]. The method is illustrated by an example. 相似文献
948.
Stephen G. Davies Ai M. Fletcher Gesine J. Hermann Giovanna Poce Paul M. Roberts Andrew D. Smith Miles J. Sweet James E. Thomson 《Tetrahedron: Asymmetry》2010,21(13-14):1635-1648
The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure N-enoyl oxazolidin-2-ones has been used as a mechanistic probe to determine that the reactive conformation is the anti-s-cis form. The β-amino carbonyl products resulting from these conjugate addition reactions are useful templates for further elaboration into an α,β,α-pseudotripeptide. 相似文献
949.
Abstract
The coordination polymer complex tetracesium bis(5-nitroisophthalate) heptahydrate [Cs4(C8H3NO6)2 (H2O)7] n has been synthesized and characterized using single-crystal X-ray diffraction. Crystals are monoclinic, space group P21/c, with Z = 4 in a cell with dimensions a = 12.3213(3), b = 6.7557(2), c = 36.2020(9) ?, β = 90.548(2)o. The complex is based on a repeating unit comprising four independent and different Cs coordination centres, two 6-coordinate, and two 8-coordinate [Cs–O, range 2.959(5)–3.386(5) ?], and seven water molecules, two of which are monodentate and the other five bridging, while all other oxygen atoms in the structure, including those of the nitro groups form inter-Cs bridges. Extensive water O–H···O hydrogen-bonding interactions give a three-dimensional framework. This structure represents the first of an alkali metal compound of 5-nitroisophthalic acid that has been reported. 相似文献950.
In this short note a Tits alternative for certain kinds of groups which are residually of rank at mostr is obtained. The main theorem states that ifG is a group that is residually (locally (soluble-by-finite) of rankr), then eitherG is locally (soluble-by-finite) orG contains a non-abelian free subgroup.
The third author would like to thank the School of Mathematics at the University of Wales, Cardiff for its hospitality whild
part of this work was being done. 相似文献