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991.
反应注射成型聚氨酯互穿聚合物网络研究——刚性网络对于体系形态及性能的影响 总被引:1,自引:0,他引:1
用微型反应注射成型机制备了以聚氨酯(PU)为弹性相的两类同步互穿聚合物网络(SIN),其刚性相分别采用保留仲羟基的乙烯基酯树脂(VERH)以及封闭仲羟基的乙烯基酯树脂(VERA)。用傅里叶变换红外光谱在线跟踪了这类互穿网络的生成过程,发现刚性网络抑制了PU网络中硬段有序结构的形成,两个网络间有一定程度的互穿,而两个网络间的化学键作用进一步削弱氢键强度。自旋—自旋弛豫时间的测定进一步表明网络间存在一定的互穿以及刚性相对于PU硬段结晶的抑制作用。材料的力学性能与其SIN的形态有关。VERA网络对PU表现出明显的增强作用,而由VERH网络形成的SIN则由于体系相分离进程受到严重阻碍而使材料性能恶化。 相似文献
992.
Pan Ziqiang Fan Shengen Cong Huiling 《Journal of Radioanalytical and Nuclear Chemistry》1996,206(2):239-249
The exposure dose status on radioisotope production and application in China has been assessed in the paper. The average annual occupational exposure dose received by workers in the radioisotope production is about one tenth of the annual dose limit in normal situation. It is less than one twentieth for workers in the radioisotope applications. However, the annual collective dose for the latter is higher than the former by one oder of magnitude due to the larger number of workers in the application field. Although the output of radioisotopes increased doubly in 1980's as compared with 1970's, the increase on the annual collective dose was not obvious. For exposure to the public,131I for example, the collective dose in the radioisotope production decreased by one to two orders of magnitude and the releasing factor reduced by two orders of magnitude. Therefore, the exposure dose received by workers in radioisotope production and application is lower in normal situation. However, the facts worth paying attention to are that there were many events and accidents which happened in the radioisotope applications, especially at the irradiation facilities. The probability of fatal accident was as high as 10–3 per irradiator year. In order to improve the radiation safety situation, it is imperative to conduct the safety assessment for irradiation facilities, to enhance management of the radioactive wastes and spent sources and to establish the experience feedback system. 相似文献
993.
994.
E. M. Araújo Renata Barbosa Amanda D. Oliveira Crislene R. S. Morais T. J. A. deMélo A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(3):811-814
Polyethylene/montmorillonite clay nanocomposites were obtained via direct
melt intercalation. The clay was organically modified with four different
types of quaternary ammonium salts. The objective of this work is to study
the use of montmorillonite clay in the production of nanocomposites by means
on rheological, mechanical and crystallization properties of nanocomposites
and to compare to the properties of the matrix and PE/unmodified clay nanocomposites.
In general, the tensile test showed that the yield strength and modulus of
the nanocomposites are close to the pure PE. Apparently, the mixture with
Dodigen salt seems to be more stable than the pure PE and PE/unmodified clay. 相似文献
995.
Sibrina N. Collins Constance M. Brett Bruce E. Bursten 《Journal of Cluster Science》2004,15(4):469-487
The photochemical CO-loss products of the diruthenium complexes [CpRu(CO) 2]2 (5; Cp = 5-C5H5), [Cp*Ru(CO)2]2 (5*; Cp* = 5-C5(CH3)5) and CpCp*[Ru(CO)2]2 (5) have been studied experimentally in low-temperature (96 K) matrices in 3-methylpentane by using IR spectroscopy. It is proposed that all three complexes undergo single-CO-loss chemistry but that the products have different structures. The single-CO-loss product from 5 is proposed to have one bridging and two terminal carbonyl ligands, whereas 5* and 5 generate triply bridged CO-loss products similar to that observed from [CpFe(CO)2]2 and [Cp*Fe(CO)2]2. Double-CO-loss from 5* and 5*
9 is also apparently observed. Relativistic DFT calculations have been carried out on various isomers of the starting materials and on potential CO-loss products from 5. The calculations suggest that the triply bridged product Cp2Ru2(-CO)3 (6) might have a singlet ground state in contrast to the corresponding diiron complex Cp2Fe2(-CO)3 (3), which has a triplet ground state. 相似文献
996.
Martin Gruebele 《Theoretical chemistry accounts》2003,109(2):53-63
Vibrational energy flow in organic molecules occurs by a multiple-time-scale mechanism that can be modeled by a single exponential
only in its initial stages. The mechanism is a consequence of the hierarchical structure of the vibrational Hamiltonian, which
leads to diffusion of vibrational wavepackets on a manifold with far fewer than the 3N−6 dimensions of the full vibrational state space. The dynamics are controlled by a local density of states, which does not
keep increasing with molecular size. In addition, the number of vibrational coordinates severely perturbed during chemical
reaction is small, leading to preservation of the hierarchical structure at chemically interesting energies. This regularity
opens up the possibility of controlling chemical reactions by controlling the vibrational energy flow. Computationally, laser
control of intramolecular vibrational energy redistribution can be modeled by quantum-classical, or by purely quantum-mechanical
models of the molecule and control field.
Received: 26 July 2002 / Accepted: 30 September 2002 / Published online: 2 December 2002
Electronic Supplementary Material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00214-002-0394-2.
Acknowledgements. This work was supported by NSF grant CHE 9986670.
Correspondence to: M. Gruebele e-mail: gruebele@scs.uiuc.edu 相似文献
997.
In situ polarized Fourier transform IR external reflection spectra of Langmuir monolayers of zinc stearate and zinc 12-hydroxystearate
on a water surface were recorded for various surface areas, and their molecular structures were estimated. In the zinc stearate
monolayer, the wavenumbers and the absorbances of the antisymmetric and symmetric methylene stretching bands did not change
during monolayer compression, which means that orientational and conformational changes of the hydrocarbon chain did not occur.
However, wavenumber changes of the antisymmetric and symmetric carboxylate stretching bands were observed during surface compression.
The change in the binding nature of the zinc cation to the carboxylate group was speculated. Moreover, it was elucidated that
the structure of the hydrocarbon chain in the zinc 12-hydroxystearate monolayer was different from that in the zinc stearate
monolayer.
Received: 21 March 2001 Accepted: 6 July 2001 相似文献
998.
Wei Wang Rongliang Wang Fan Wu Boshun Wan 《Reaction Kinetics and Catalysis Letters》2005,85(2):277-282
Summary A Ni-promoted ligand free palladium catalyst system for Suzuki coupling of aryl bromides has been developed in high efficiency under mild reaction conditions. It was obtained in situ by introducing NiCl2 to PdCl2/PVP using a parallel high-throughput screening technique. A wide range of aryl bromides bearing a variety of functional groups was evaluated. 相似文献
999.
Ivan Gutman 《Monatshefte für Chemie / Chemical Monthly》2005,136(6):1055-1069
Summary. The fact that cyclic arrangements of double bonds have a dramatic effect on the behavior of conjugated organic molecules is known since the 19th century. The fact that in monocyclic conjugated systems the size of the cycle and the number of -electrons involved is decisive for their stability (aromaticity) or lack of stability (antiaromaticity) is known since the 1930s. In polycyclic -electron systems several cyclic effects are present simultaneously and their separation became possible only recently. A molecular orbital method has been elaborated, by means of which the energy effects of individual cycles in polycyclic -electron systems can be estimated. This method is briefly outlined and illustrated by pertinent examples. An exhaustive bibliography of the topic considered is given. 相似文献
1000.
Claudia Mureşanu Lucian Copolovici Florina Pogącean 《Central European Journal of Chemistry》2005,3(4):592-604
The inhibitory effect of para-nitrophenol on the catalytic reaction of catalase was investigated. Michaelis-Menten kinetic parameters were determined from
Lineweaver-Burk plots obtained in the absence or in the presence of the inhibitor. The inhibitor pattern, revealed by the
Lineweaver-Burk plots, suggested a fully mixed inhibition mechanism. Spectrophotometric monitoring of the indicator reaction:
in conjunction with initial rate measurements was employed for the kinetic determination of the inhibitor. Calibration plots
of initial rate vs. para-nitrophenol concentration were linear in the concentration range 0.9·10−5–2.5·10−5 mol/L and the detection limit was 3·10−6 mol/L (417 μg/L) para-nitrophenol. Interferences from other phenolic compounds like orto-cresole, meta-and orto-nitrophenol were observed. 相似文献