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排序方式: 共有131条查询结果,搜索用时 78 毫秒
91.
The novel monomer, π-(2, 4-hexadiene- l-yl acrylate) tricarbonyliron (HATI), has been prepared by two routes. It was homopolymerized and copolymerized with acrylonitrile, vinyl acetate, styrene, and methyl acrylate in benzene solutions. In all cases azobisisobutyronitrile was the initiator. The relative reactivity ratios, where HATI is defined as M1, were determined: r1 = 0.34, r2 = 0.74, M2 = acrylonitrile; r1 = 2.0, r2 = 0.05, M2 = 0.74, M2 = acrylonitrile; r1 = 2.0, r2 = 0.05, M2 = vinyl acetate; r1 = 0.26, r2 = 1.81, M2 = styrene; and r1 = 0.30, r2 = 0.74, M2 = methyl acrylate. The homo-and copolymers had high values of Tg. When polymerizations are carried out at high concentrations, a very high molecular weight tail is observed in HATI hompolymerizations and in HATI-methyl acrylate copolymerizations. The polymers were characterized by IR, gel permeation chromatography, viscosity, and differential scanning calorimetry studies. Finally, thermal decompositions carried out in air resulted in decomposition of the Fe(CO)3 group, producing Fe2O3 as a fine powder. Thermal decomposition under nitrogen (in solution and on solids ground into KBr pellets) resulted in slow destruction of the Fe(CO)3 groups but the resulting polymer mass was insoluble, and the question of what form the iron exists in (Fe metal, oxides, carbides, etc.) has not been answered. 相似文献
92.
Mixtures of methane and olefins (ethylene, propylene, butenes, butadiene, and styrene) have been polymerized over HSO3 F-SbF3 to yield an oily oligomer with a molecular weight ranging from 100 to 700. The NMR spectra of each polymer showed a sharp peak at or near 1.25 &, suggesting the presence of block methylene in the polymer. The formation of block methylene is surprising considering the fact that the polymerization reaction is carbonium ion in nature. A primary cation has been invoked to explain the results. The formation of this primary cation must involve some extraordinary stabilization by some component in the acid. 相似文献
93.
G.W. SWENSON JR 《Journal of sound and vibration》2002,255(3):519-529
A directional microphone system for field recording of sounds in the air often involves a parabolic reflector to focus the sound waves on the microphone (transducer) element. Some deficiencies of such a system are noted with respect to reproduction of spectra. The reflector system, involving as it does a structure comparable to a wavelength in linear dimension, is not susceptible to traditional high- or low-frequency approximate methods of computation. Modern numerical techniques now permit precise calculation of the directional responses of small reflectors of various shapes. One result is a proposal for a very economical and effective system involving a plane reflector. Other baffle shapes are also investigated, which may be of interest in special applications. 相似文献
94.
H Pledger JR. G.-S. Wu T. S. Young T. E. Hogen-esch G. B. Butler 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):1297-1307
Graft copolymers of acrylamide and yellow dextrin were prepared using cerium(IV) as initiator. The yellow dextrin had a very broad molecular weight distribution but was fractionated utilizing dialysis and ultrafiltration membranes. Initiator efficiencies were determined using size exclusion chromatography and were found to be between 2.4 and 34%. Initiator efficiency increased with acrylamide concentration at constant cerium (IV) and yellow dextrin concentrations, and decreased with increasing cerium(IV) concentration at constant acrylamide and yellow dextrin concentrations. Plots of acrylamide conversion and intrinsic viscosity vs initial acrylamide concentration at constant yellow dextrin and ceric ion concentrations showed a maximum at about 2.0 M. 相似文献
95.
96.
This paper is concerned with the construction and analysis ofcompact finite difference approximations to the model linearsource problem (pu')' + qu = f where the functions p,q, and f can have jump discontinuities at a finite number ofpoints. Explicit formulae that give O(h2) O(h3) and O(h4) accuracyare derived, and a procedure for computing three-point schemesof any prescribed order of accuracy is presented. A rigoroustruncation and discretization error analysis is offered. Numericalresults are also given. 相似文献
97.
H. E. Marsh JR. 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):1397-1418
Abstract The complex and important role of the propellant binder in solid-propellant rockets is described. The severe weight problems of space exploratrion cause high propellant performance to be of major concern in a highly competitive field. Binders contribute to performance, not only in terms of fuel value, but by being compatible with energetic components and by providing good mechanical properties. Both sterilization required for planetary landings and compatibility problems of new energetic oxidizers generate new requirements too stringent for existing binders; only binders composed essentially of saturated aliphatic hydrocarbon are predicted to be suitable. Several saturated-binder developments are in progress. The achievements of one of these programs, based on free-radical synthesis, are evaluated against the goals of the new binder. 相似文献
98.
Volodymyr Gvozdetskyi Gourab Bhaskar Maria Batuk Xin Zhao Renhai Wang Scott L. Carnahan Michael P. Hanrahan Raquel A. Ribeiro Paul C. Canfield Aaron J. Rossini Cai‐Zhuang Wang Kai‐Ming Ho Joke Hadermann Julia V. Zaikina 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(44):16002-16009
Two novel lithium nickel boride polymorphs, RT‐LiNiB and HT‐LiNiB, with layered crystal structures are reported. This family of compounds was theoretically predicted by using the adaptive genetic algorithm (AGA) and subsequently synthesized by a hydride route with LiH as the lithium source. Unique among the known ternary transition‐metal borides, the LiNiB structures feature Li layers alternating with nearly planar [NiB] layers composed of Ni hexagonal rings with a B–B pair at the center. A comprehensive study using a combination of single crystal/synchrotron powder X‐ray diffraction, solid‐state 7Li and 11B NMR spectroscopy, scanning transmission electron microscopy, quantum‐chemical calculations, and magnetism has shed light on the intrinsic features of these polymorphic compounds. The unique layered structures of LiNiB compounds make them ultimate precursors for exfoliation studies, thus paving a way toward two‐dimensional transition‐metal borides, MBenes. 相似文献
99.
J. Runt B. D. Hanrahan I. R. Harrison 《Journal of Polymer Science.Polymer Physics》1982,20(9):1687-1693
The fold periods and longitudinal acoustic modes [LAMs] for isothermally crystallized polyethylene (PE) single crystals were determined in the dried state and in the presence of decalin and silicone oil. Upon swelling with decalin, the fold period increased by 7% while the LAM peak frequency decreased by approximately 1 cm?1. Several possible explanations for the change in LAM frequency are discussed but the exact interpretation is open to question. No change in fold period was observed upon soaking a dried crystal mat in silicone oil. This fold period invariance along with the fact that silicone oil has no effect on the melting point of PE crystals indicates that there is no significant interaction between the oil and the methylene groups on the crystal surface. The effect of suspending crystals (which have never been dried down) in silicone oil should only be to increase the average interlamellar distance and, therefore, to reduce any interlamellar forces. It is shown that the LAM peak frequency for crystals suspended in silicone oil is the same as that for the dried crystals, indicating that interlamellar forces do not exert a significant perturbing influence on the LAM of polyethylene crystals. 相似文献
100.