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71.
Dusanka Ž. Obadović Anikó Vajda Maya Garić A. Bubnov Vera Hamplová M. Kašpar Katalin Fodor-Csorba 《Journal of Thermal Analysis and Calorimetry》2005,80(2):519-523
Summary Thermal properties of a homologous series of ferroelectric liquid crystals S-(-)-[4-(2-n-alkoxy-propionyloxy)]biphenyl-4'-[n-alkoxy-(3,5-dimethyl)]benzoate have been investigated by polarizing optical microscopy and differential scanning calorimetry.
The mesophases were identified and confirmed by X-ray too. Three binary mixtures were prepared from the individual homologues.
In one of the mixtures (Mix1), the ferroelectric SmC* phase has broadened and became enantiotropic. This mesophase remained
monotropic in the other two mixtures (Mix2, Mix3). The chiral nematic N* phase did not appear in Mix1, but remained monotropic
for the other two mixtures. Two molecular parameters, the layer spacing and the average intermolecular distance have been
calculated from the X-ray results for the homologues and their mixtures. An intercalated tail-to-tail packing of molecules
was found both in the single compounds and their mixtures resulting in the layer spacing about half of the molecular length
of the single compounds. 相似文献
72.
73.
Beltrami I Bylsma BG DeBonte R Gan KK Koltick D Loeffler FJ Low EH McIlwain RL Miller DH Ng CR Ong PP Rangan LK Shibata EI Wilson RJ Derrick M Fernandez E Fries R Hyman L Kooijman P Loos JS Musgrave B Price LE Schlereth J Sugano K Weiss JM Wood DE Baranko G Baringer P Blockus D Brabson B Forden GE Gray SW Jung C Neal H Ogren H Rust DR Valdata-Nappi M Akerlof C Bonvicini G Chapman J Errede D Harnew N Kesten P Kooijman S Meyer DI Nitz D Rubin D Seidl AA Thun R Trinko T Willutzky W Cork B Keller L 《Physical review letters》1985,54(16):1775-1778
74.
Winghong Chan Suei Yee Lam-Leung Chingfai Ng Junqi Ding Shiping Xi 《Journal of polymer science. Part A, Polymer chemistry》1995,33(15):2525-2531
New diamino monomers IIa – IIg were synthesized in a two-step reaction sequence starting from p-acetamidobenzenesulfonyl chloride. Solution polymerization of these monomers in DMAC with terephthaloyl or isophthaloyl chloride resulted in the formation of a series of 14 poly(amide sulfonamide)s (PASAs) in excellent yield (> 95%). The polymers have in-trinsic viscosities of 0.32–1.11 dL g?1. Except for polymers IIIa ? p and IIId - p , all other PASAs were readily soluble in aprotic polar solvents including DMAC, DMF, and DMSO. Thermogravimetric analyses of the polymers showed moderate thermal stability with 10% weight loss being recorded in the range of 325–408°C. In addition, these polymers exhibit moderate chemical stabilities toward alkali, acidic, and chromic acid solution. © 1995 John Wiley & Sons, Inc. 相似文献
75.
Vlastimil Matějec Ivan Kašík Daniela Berková Miloš Hayer Jiří Kaňka 《Journal of Sol-Gel Science and Technology》1998,13(1-3):617-621
Optical cores of preforms for drawing optical fibers doped with Er3+ and Yb3+ were fabricated by the sol-gel method with the aim of increasing the thickness of glass layers coated in a single coating cycle and to determine the relation between the preparation conditions and optical properties of the fibers. Al2O3-P2O5-SiO2 and TiO2-P2O5-SiO2 glasses have been studied as matrices for entrapping the rare-earth elements. Input sols have been prepared from silicon and titanium alkoxides, AlCl3, ErCl3, YbCl3, POCl3, water and a modifier under acidic catalysis of HCl. The sols were coated on the inner wall of a silica substrate tube and the gel layers were sintered at high temperatures up to 2000°C after which the tube was collapsed into the preform. Continuous and homogenous glass films with the maximum thickness of about 8 m were fabricated. The influence of high-temperature heat treatment of the layers on their composition and optical attenuation was observed. The amplified stimulated emission of Er3+ around 1.55 m was measured under the excitation of the fibers by an Nd : YAG laser at 1.064 m. 相似文献
76.
The phosphapalladacycle derived from 1-(2',5'-dimethylphenyl)ethyldiphenylphosphine has been prepared in the optically active and racemic forms. The phosphine was synthesized as a racemate by the treatment of 1-chloro-1-(2',5'-dimethylphenyl)ethane with sodium diphenylphosphide in THF. The racemic phosphapalladacycle was subsequently obtained as the chloro-bridged dimer by the treatment of the phosphine with palladium(II) acetate followed by anion metathesis with lithium chloride. Alternatively, the phosphine could be optically resolved via metal complexation using (R,R)-bis(mu-chloro)bis{1-[1-(N,N-dimethylamino)ethyl]naphthyl-C(2),N}dipalladium(II) as the resolving agent. An efficient separation of the resulting diastereomeric complexes was achieved by silica gel chromatography. The obtained optically resolved diastereomers were next subject to chemoselective removal of the (R)-N,N-(dimethylamino)-1-(1-naphthyl)ethylaminate auxiliary by treatment with concentrated hydrochloric acid. This process yielded the binuclear dimer complexes containing the resolved eta(1)-P ligand. Cyclopalladation of the coordinated phosphine could next be performed by treatment of its eta(1)-P binuclear dimer with silver(I) hexafluorophosphate(V) in a dichloromethane/water mixture followed by treatment with lithium chloride, giving rise to a pair of optically pure enantiomeric dimers with [alpha](D) -322 and +319 degrees in CH(2)Cl(2). Despite the possibilities of the phosphine to attain a five- membered structure by ortho-palladation or a six-membered ring formation by aliphatic C-H bond activation, only the former was observed. X-ray crystallographic data of the meso dimer and an acetylacetonate derivative indicated that the phosphapalladacycle alpha-C methyl substituent was axially located. The 2-D (1)H-(1)H ROESY spectrum of the acetylacetonate derivative further revealed that the phosphapalladacycle was conformationally rigid in CDCl(3). 相似文献
77.
The reactions of π-cyclopentadienylnickel carbonyl dimer with 3,3,3-trimethylpropynyldiphenylphosphine and phenylethynyldiphenylphosphine are described. The products have been characterized by elemental and mass spectral analysis, infrared and NMR spectroscopy. An acetylene bridged complex (π-C5H5Ni)2Ph2PC2-t-Bu, containing an uncoordinated phosphorus atom, has been prepared. The complex can be oxidized to the phosphine oxide derivative (π-C5H5Ni)2Ph2P(O)C2-t-Bu and converted to the phosphonium salts with methyl iodide or ethyl bromide. These are the first reported π-complexes of phosphonium salts. The complex (π-C5H5Ni)2Ph2PC2-t-Bu forms the novel mixed metal derivative [PdCl2][(π-C5H5Ni)2Ph2PC2-t-Bu]2 from bis(benzonitrile)-palladium dichloride. The dicarbonyl complexes Ni(CO)2(Ph2PC2R)2 (R t-Bu, Ph), the phosphine oxide complex (π-C5H5Ni)2(Ph2P(O)C2Ph) and the trinuclear nickel carbonyl derivative Ni(CO)3[(π-C5H5Ni)2Ph2PC2Ph] are described. 相似文献
78.
Four new chiral stationary phases based on mono-(6A-allylcarbamido-6A-deoxy)-arylcarbamoylated β-cyclodextrin were synthesized. The chiral stationary phase of phenylcarbamoylated β-cyclodextrin exhibited excellent separation capability for a variety of chiral compounds. Compared with the previous work, it was found that the spacer remained on the surface of the silica gel and decreased the enantioseparation capability. 相似文献
79.
Experimental data on initial hydrate formation conditions have been obtained for the nitrogen-propane-water system in the L1HG, L1L2H, and L1L2HG regions, where L1 is the water rich liquid phase, L2 is the hydrocarbon rich liquid phase, H is the hydrate and the G is the vapor phase. The measurements covered a range of temperatures from about 275 to 293 K and pressures from about 0.3 to 17.0 MPa. The concentrations covered for the L1HG region extended from 0.94 to 75.0 mole percent propane in the gas phase, and for the L1L2H region they extended from 83.1 to 99.0 mole percent in the condensed liquid phase. Four-phase measurements were made at concentrations of propane from 18.1 to 71.1 mole percent in the gas phase.The experimental data were used to find a fitted binary interaction parameter for predicting hydrate formation in systems containing nitrogen and propane. 相似文献
80.