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排序方式: 共有1007条查询结果,搜索用时 46 毫秒
11.
Hoh-Jiear Yan Eli M. Pearce 《Journal of polymer science. Part A, Polymer chemistry》1984,22(11):3319-3334
Polymers containing rigid aromatic structures in the chain backbone usually gave high thermal stability and good flammability resistance. Three glycidyl ethers of epoxy resins were prepared from 2,4-di(p-hydroxystyryl)pyridine (2,4-DGESP), 2,6-di-(p-hydroxystyryl)pyridine (2,6-DGESP), and 2,4,6-tri-(p-hydroxystyryl)pryidine (2,4,6-TGESP) to study the relationships of structure to polymer degradation. To prepare a highly crosslinked material, trimethoxyboroxine (TMB) was used as the curing agent. The relative char yields of the three different resins, as measured by TGA, were 2,4-DGESP ≈ 2,6-DGESP > 2,4,6-TGESP. The char yield of the cured 2,6-DGESP varied with different amounts of the TMB curing agent, and was higher than the uncured 2,6-DGESP. The oxygen index increased as a function of thermal curing time for the 2,6-DGESP epoxy resin. An intermolecular Diels–Alder reaction with 2,6-DGESP is proposed as a primary reaction during thermal curing. 相似文献
12.
Binoy K. Bordoloi Eli M. Pearce L. Blight B. R. Currell R. Merrall R. A. M. Scott C. Stillo 《Journal of polymer science. Part A, Polymer chemistry》1980,18(2):383-406
Liquid sulfur–olefinic reactions at 140°C forming crosslinked polysulfide polymers have been investigated. A systematic approach to the characterization and some structure–property studies on these new polymeric materials has been presented. The olefinic systems of interest are endo-and exo-dicyclopentadiene and an oligomeric alkenyl polysulfide. Equimolar S8–olefinic system copolymers are amorphous and they show no tendency for sulfur crystallization. A correlation has been drawn between chemical structure and glass transition temperature of the copolymers and terpolymers. Mechanical properties and, in particular, chemical stress relaxation of the crosslinked polysulfide polymers have been investigated. 相似文献
13.
Pollak C Malic B Kosec M Javoric S Hutter H 《Analytical and bioanalytical chemistry》2002,374(4):608-613
Chemical solution-deposited thin films of PbZr(0.53)Ti(0.47)O(3)/La(0.5)Sr(0.5)CoO(3) on Pt/TiO(2)/SiO(2)/Si substrates have been investigated by dynamic SIMS. The PbZr(0.53)Ti(0.47)O(3) (PZT) is intended to serve as a ferroelectric layer for microelectronic or microelectromechanical applications; conducting La(0.5)Sr(0.5)CoO(3) (LSCO) is a buffer layer intended to eliminate fatigue effects which usually occur at the Pt/PZT interface. Depth profiles of the main components were obtained and revealed that significant diffusion occurred during the deposition and crystallisation processes. Two types of sample, with different thickness of PZT and different types of poly(vinyl alcohol) (PVA) added to the LSCO precursor, were investigated. 相似文献
14.
A new and experimental photodensitometer designed for quantitative chromatography is described. The principal features of the instrument were based upon the results of an extensive theoretical analysis and incorporate a mechanical arrangement for the production fo a flying spot and an optical path in which two beams of light are separated after interaction with the medium. The device is constructed so as to be suitable for operation in the three principal modes; in reflectance measurements only the ratio of the beam signals is formed, whilst in transmittance measurements the ratio is converted to logarithmic form, in the fluorescence mode only a single beam is used. The spectral range of the instrument extends from the red end of the visible spectrum to the medium ultraviolet, and quartz optics are utilized in most of the optic elements. A quartz halogen lamp and a xenon-mercury lamp may be used alternatively as the light source. Changeable interference filters are employed to determine the spectral position of the light beams and semiconductor photo-diodes with sensitivities extending into the ultraviolet are used as photo-detectors. In the determination of the sensitivity limits of the device the photo-diodes were replaced by photomultipliers and the apparatus was shown to fulfil most of the calculated thoeretical predictions. 相似文献
15.
The reaction of aromatic thiols with sulfur dichloride and sulfur monochloride to form the corresponding aromatic trisulfides, 2a-d, and tetrasulfides, 3a-d, has been optimized with respect to yield and purity. The use of pyridine as an amine base and the use of freshly distilled sulfur monochloride (S(2)Cl(2)) serve as important alterations to the synthetic method. Their physical properties have been characterized, revealing some discrepancies with the literature. 相似文献
16.
S. H. Kim Eli M. Pearce T. K. Kwei 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3167-3180
The precursor of polybenzimidazole (PBI), poly(3,3′-diamino-4,4′-benzidine isophthalamide) (PDABI), was synthesized from poly(3,3′-dinitro-4,4′-benzidine isophthalamide) (PDNBI) by reduction. With increasing temperature, the NH2 moiety which was protected by SnCl5?1 could cyclize and form PBI. Blends with polyamic acid (LaRC-TPI) were prepared. Clear blend films were prepared at up to 400°C. The IR spectra displayed shifts in the NH stretching band, thereby providing evidence for specific interactions related to the miscibility of their cured blends. © 1993 John Wiley & Sons, Inc. 相似文献
17.
Elena Levi Eli Lancry Yossi Gofer Doron Aurbach 《Journal of Solid State Electrochemistry》2006,10(3):176-184
A crystallographic approach was applied to elucidate the influence of the nature of the surface films on the electrochemical
behavior of Li and Mg intercalation compounds. This paper presents two examples: (1) protection of graphite electrodes by
Li2CO3 surface films, and (2) the unique electrochemical behavior of Mg-containing Chevrel phases (MgCP) obtained by different synthetic
routes. In the former case, the elucidation of the protection mechanism and the explanation of the high performance of such
protected electrodes are based on the analysis of possible Li-ion motion in the carbonate crystal structure. In the latter
case, a combination of synthesis, electrochemistry and XRD analysis was used to explain an unusual phenomenon: the difference
between the excellent electrochemical behavior of the Chevrel phase (CP) based on Cu-leached Cu2Mo6S8 (CuCP), and the poor electrochemical activity of the high-temperature synthesized MgCP, with the same phase composition.
It is shown that this phenomenon is caused by MgO formation on the surface of the latter material. The different surface chemistry
of the MgCPs obtained by the two different synthetic routes was substantiated by revealing the correlation between the electrochemical
activity and the chemical stability of these materials under ambient atmosphere conditions.
Dedicated to Prof. Mikhail A. Vorotyntsev on the occasion of his 60th birthday. 相似文献
18.
A Franck—Condon type argument, which requires the least transfer of momenta to the nuclei during a collision is outlined and applied to the analysis of translational energy disposal and its dependence on the initial translational energy. Using the maximal entropy procedure of information theory we are able to proceed directly from the assumed (model) constraint to the product state distribution. 相似文献
19.
Journal of Algebraic Combinatorics - The well-known Worpitzky identity $$\begin{aligned} (x+1)^n = \sum \limits _{k=0}^{n-1} A_{n,k} {{x+n-k} \atopwithdelims (){n}} \end{aligned}$$ provides a... 相似文献
20.
Eli Glasner 《Journal d'Analyse Mathématique》1994,64(1):241-262
For a minimal distal flow (X, T) and a positive integern, let be the largest distal factor of ordern. The existence of a denseG
δ subset ω ofX is shown, such that forx ∈ ω the orbit closure of (x,x,...,x) ∈ X
n+1 under τ =T ×T
2 ... ×T
n+1 is π-saturated. In fact, an analogous statement for a general minimal flow is proved in terms of its PI-tower. On the way
we get some topological “ergodic” decomposition theorems. 相似文献