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921.
I. Pinnau C. G. Casillas A. Morisato B. D. Freeman 《Journal of Polymer Science.Polymer Physics》1996,34(15):2613-2621
The gas permeation properties of poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and blends of PTMSP and PPP have been determined with hydrocarbon/hydrogen mixtures. For a glassy polymer, PTMSP has unusual gas permeation properties which result from its very high free volume. Transport in PPP is similar to that observed in conventional, low-free-volume glassy polymers. In experiments with n-butane/hydrogen gas mixtures, PTMSP and PTMSP/PPP blend membranes were more permeable to n-butane than to hydrogen. PPP, on the other hand, was more permeable to hydrogen than to n-butane. As the PTMSP composition in the blend increased from 0 to 100%, n-butane permeability increased by a factor of 2600, and n-butane/hydrogen selectivity increased from 0.4 to 24. Thus, both hydrocarbon permeability and hydrocarbon/hydrogen selectivity increase with the PTMSP content in the blend. The selectivities measured with gas mixtures were markedly higher than selectivities calculated from the corresponding ratio of pure gas permeabilities. The difference between mixed gas and pure gas selectivity becomes more pronounced as the PTMSP content in the blend increases. The mixed gas selectivities are higher than pure gas selectivities because the hydrogen permeability in the mixture is much lower than the pure hydrogen permeability. For example, the hydrogen permeability in PTMSP decreased by a factor of 20 as the relative propane pressure (p/psat) in propane/hydrogen mixtures increased from 0 to 0.8. This marked reduction in permanent gas permeability in the presence of a more condensable hydrocarbon component is reminiscent of blocking of permanent gas transport in microporous materials by preferential sorption of the condensable component in the pores. The permeability of PTMSP to a five-component hydrocarbon/hydrogen mixture, similar to that found in refinery waste gas, was determined and compared with published permeation results for a 6-Å microporous carbon membrane. PTMSP exhibited lower selectivities than those of the carbon membrane, but permeability coefficients in PTMSP were nearly three orders of magnitude higher. © 1996 John Wiley & Sons, Inc. 相似文献
922.
A. Morisato H. C. Shen S. S. Sankar B. D. Freeman I. Pinnau C. G. Casillas 《Journal of Polymer Science.Polymer Physics》1996,34(13):2209-2222
Pure gas and hydrocarbon vapor transport properties of blends of two glassy, polyacetylene-based polymers, poly(1-trimethylsilyl-1-propyne) [PTMSP] and poly(1-phenyl-1-propyne) [PPP], have been determined. Solid-state CP/MAS NMR proton rotating frame relaxation times were determined in the pure polymers and the blends. NMR studies show that PTMSP and PPP form strongly phase-separated blends. The permeabilities of the pure polymers and each blend were determined with hydrogen, nitrogen, oxygen, carbon dioxide, and n-butane. PTMSP exhibits unusual gas and vapor transport properties which result from its extremely high free volume. PTMSP is more permeable to large organic vapors, such as n-butane, than to small, permanent gases, such as hydrogen. PPP exhibits gas permeation characteristics of conventional low free volume glassy polymers; PPP is more permeable to hydrogen than to n-butane. In PTMSP/PPP blends, both n-butane permeability and n-butane/hydrogen selectivity increase as the PTMSP content of the blends increases. © 1996 John Wiley & Sons, Inc. 相似文献
923.
This work was focused on the influence of the morphology of composite natural rubber (NR)-based particles on the toughness of poly(styrene–co-acrylonitrile) (PSAN) blends. In order to be suitable for the reinforcement of PSAN blends, the NR-based particles were coated with a shell of crosslinked poly(methylmethacrylate) (PMMA). Furthermore, polystyrene (PS) subinclusions were introduced into the NR rubber core. PSAN blends were prepared by adding the wet latex directly into a twin screw-extruder. This new method allowed even tacky pure rubber particles to be dispersed as shown by transmission electron photomicrographs which confirmed the integrity of the soft particles after mixing. Solid NR particles or NR-based latex particles containing rigid PS subinclusions and no hard shell did not offer any impact improvement to PSAN. Only NR-based core–shell particles containing at least 25% PMMA in the shell toughened the brittle matrix. Prevulcanized NR-based latex particles which do not cavitate easily were less effective. Core–shell particles containing PS subinclusions within a natural rubber core allowed more effective use of the rubber phase. From the fracture surface morphology the failure mechanisms of PSAN blends containing the different composite NR particles could be deduced. Monodisperse poly(n-butylacrylate)-based core–shell particles were too small to toughen PSAN. However, a similar dependence of the fracture mechanisms on the morphology of the incorporated toughening agent could be established by scanning electron microscopy. 相似文献
924.
925.
研究了AVS音频编码标准中上下文位平面编码算法,分析了编码算法的特点。通过对上下文平面编码算法的优化,提出了一种适合ASIC实现的硬件结构,通过合理设计二级流水线,能近似达到每时钟1比特矢量的编码速率,在保证编码速度前提下大幅降低了硬件资源。 相似文献
926.
Pure enantiomers of chiral (atropisomeric) polychlorinated biphenyls (PCBs) obtained by high-performance liquid chromatography were used to establish the gas chromatographic elution sequences of the (+)- and (−)-enantiomers of six PCB atropisomers on Chirasil-Dex. The elution order was found to be (−/+) for PCBs 84, 132, 136, and 176 and (+/−) for PCBs 135 and 174. The retention characteristics of all 19 tri- and tetra-ortho atropisomeric PCBs were also investigated. Nine of the atropisomers could be separated using this chiral selector. PCBs 95, 132, and 149 were completely resovled and PCBs 84, 91, 135, 136, 174, and 176 were partially separated (R = 0.7–0.9). All of the separated congeners are 2,3,6-substituted in at least one ring, and conversely – none of the congeners that lacks 2,3,6-substitution could be separated. Thus, chiral recognition and enantiomer separation seems to be strongly governed by 2,3,6-substitution. 相似文献
927.
928.
High resolution gas chromatography (HRGC) coupled to a “purge and trap” extraction-injection technique is described as a method of determining 1,2,4-trichlorobenzene in water at levels as low as parts-per-trillion (ppt). In order to investigate the interference from other volatile organic compounds (VOCs) several detection systems were compared: flame ionization, electron capture, and mass spectrometry-multiple ion detection. Concentrations ranging from 15 to 600 ng/L were analyzed in 20 ml standard aqueous solutions. The mean accuracy of the method varied from 89 to 103%, and its mean precision varied from ± 0.85 to ± 7.5 % for all detectors. The detection limits were 20 ng/L for FID, 2 ng/L for ECD and 0.5 ng/L for MID-MS detectors. The procedure was successfully applied to the analysis of industrial waste waters. The necessity of an appropriate internal standard to improve the quantitative determination and to determine possible losses or degradation of 1,2,4-trichlorobenzene during handling or storage is discussed. 相似文献
929.
930.