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891.
Norman G. Gaylord Birendra K. Patnaik 《Journal of polymer science. Part A, Polymer chemistry》1975,13(4):837-855
Neighboring monomer units cause significant shifts in the infrared absorption peaks attributed to cis- and trans-1,4 units in conjugated diene-acceptor monomer copolymers. Conjugated diene-maleic anhydride alternating copolymers apparently have a predominantly cis-1,4-structure, while alternating diene-SO2 copolymers have a predominantly trans-1,4 structure. Alternating copolymers of butadiene, isoprene, and pentadiene-1,3 with α-chloroacrylonitrile and methyl α-chloroacrylate, prepared in the presence of Et1.5AlCl1.5(EASC), have trans-1,4 unsaturation. Alternating copolymers of chloroprene with acrylonitrile, methyl acrylate, methyl methacrylate, α-chloroacrylonitrile, and methyl α-chloroacrylate prepared in the presence of EASC-VOCl3 have trans-1,4 configuration. The reaction between chloroprene and acrylonitrile in the presence of AlCl3 yields the cyclic Diel-Alder adduct in the dark and the alternating copolymer under ultraviolet irradiation. The equimolar, presumably alternating, copolymers of chloroprene with methyl acrylate and methyl methacrylate undergo cyclization at 205°C to a far lesser extent than theoretically calculated, to yield five and seven-membered lactones. The polymerization of chloroprene in the presence of EASC and acetonitrile yields a radical homopolymer with trans-1,4 unsaturation. 相似文献
892.
A generalized method for synthesizing a wide variety of heterocyclic aromatic amine derivatives from nitriles by use of hydroxide catalysts is presented. Nitrile dimers (3-aminocrotononitrile and dicyandiamide) and a dimer analog (anthranilonitrile) react with monomeric nitriles in the presence of hydroxide to form respectively, aminopyrimidines, diaminotriazines and aminoquinazolines. 相似文献
893.
894.
Norman S. Allen Jean-Luc Gardette Jacques Lemaire 《Polymer Degradation and Stability》1982,4(4):261-266
The effect of a hindered piperidine compound and stable nitroxyl radical on the thermal reduction of p-benzoquinone in polypropylene has been examined using ESR, uv-visible and fluorescence spectroscopy. Thermal reduction to hydroquinone was inhibited by both compounds. With the hindered amine the nitroxyl radical was regenerated through the formation of the hydroxylamine whereas, with the nitroxyl radical, there was quantitative conversion to the hydroxylamine and no nitroxyl radical regeneration. Both inhibition processes were found to antagonise the photo-stabilising action of the hindered piperidine compounds due to the regeneration of the quinone. 相似文献
895.
Inmaculada Fernandez Robert Greatrex Norman N. Greenwood 《Journal of solid state chemistry》1980,32(1):97-104
57Fe and 99Ru Mössbauer spectroscopy, coupled with magnetic susceptibility measurements down to 4.2 K, have been used to study the electronic and magnetic properties of the new cubic-ordered perovskites BaLaMRuO6 (M = Mg, Fe, Co, Ni, or Zn). The ruthenium is present in the +5 oxidation state in all the compounds except BaLaFeRuO6 which contains iron(III) and ruthenium(IV). All the compounds exhibit long-range antiferromagnetic order, with Néel temperatures in the range 20–40 K. Mössbauer spectra for the new compound La2CoRuO6 and the isostructural cubic perovskites La2MRuO6 (M = Mg, Ni, or Zn) confirm the presence of ruthenium(IV) in these phases and indicate that they are not ordered magnetically at 4.2 K. 相似文献
896.
Krishnamurthy LN Weigert EC Wagner NJ Boris DC 《Journal of colloid and interface science》2004,280(1):264-275
A micromechanical model for the zero shear viscosity of polyampholyte-stabilized colloidal dispersions based on the osmotic overlap potential is proposed and tested against model system measurements. This model relates the shear viscosity of polyampholyte-stabilized colloidal dispersions to the oncotic pressure of polyampholyte solutions through an interparticle potential and an effective hard-sphere scaling. The results of viscosity calculations based on independently measured parameters compare favorably to experimental measurements on model, silica dispersions stabilized with adsorbed photographic grade gelatin. The results support a direct link between the capacity of polyampholytes and polyelectrolytes to stabilize dispersions and control dispersion viscosity and their solution oncotic pressure. The model is also demonstrated to provide a master curve for literature data for the zero shear viscosity of polyampholyte stabilized colloidal dispersions. 相似文献
897.
Let be a translation plane of odd order p2R for p a prime. Let admit at least two p-groups, Bi, i=1, 2, B1B2 of orders > pR/2 which fix Baer subplanes i, i = 1,2, 12 pointwise. It is shown that under these assumptions must be a Hall plane. 相似文献
898.
899.
900.
Summary The argument principle is a natural and simple method to determine the number of zeros of an analytic functionf(z) in a bounded domainD. N, the number of zeros (counting multiplicities) off(z), is 1/2 times the change in Argf(z) asz moves along the closed contour D. Since the range of Argf(z) is (–, ] a critical point in the computational procedure is to assure that the discretization of D, {z
i
,i=1, ...,M}, is such that
. Discretization control which may violate this inequality can lead to an unreliable algorithm. Mathematical theorems derived for the discretization of D lead to a completely reliable algorithm to computeN. This algorithm also treats in an elementary way the case when a zero is on or near the contour D. Numerical examples are given for the reliable algorithm formulated here and it is pointed out in these examples how inadequate discretization control can lead to failure of other algorithms.Dedicated to Professor Ivo Babuka in commemoration of his sixtieth birthdayThis research is part of the doctoral dissertation of this author 相似文献