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71.
Sofiane Ben Hamouda Quang Trong Nguyen Pierre Schaetzel 《European Polymer Journal》2006,42(11):2994-3005
Ethylene/ethane sorption characteristics were determined for dry Pebax™ (poly(amide 12-block-tetramethylenoxide) copolymer)/AgBF4 membranes by using an electronic microbalance. The membranes containing 0.7 and 22 wt.% AgBF4 showed a dual-mode sorption isotherm. The ethane isotherms for all the membranes were of the Henry-type, which is the normal sorption for gases in rubbery polymers. The abnormal presence of Langmuir sorption sites only for ethylene in the rubbery copolymer, never reported sofar, is attributed to the silver-based specific complexation sites. The silver salt which dissolved in limited amounts in the rubbery copolymer had a much smaller Langmuir sorption capacity than the salt that crystallized in the copolymer. The sorption kinetics indicate that the crystallized salt did adsorb slowly ethylene according to a zeroth-order kinetics, but not ethane. The gas uptake kinetics resulting from a step of the pressure surrounding the copolymer exhibited one stage for ethane but two stages for ethylene. For the latter, there was first a fast Fickian sorption stage, then a drift of the zeroth-order sorption of ethylene on salt crystals, which contributes for a large part to the total uptake. The zeroth-order sorption suggests that the sorbed ethylene amount in the second-stage is independent of the crystal-surface coverage. The value of the Fickian diffusion coefficient calculated by fitting the kinetics with a solution of the second Fick’s law was 5 × 10−12 m2/s for both ethylene (the first stage) and ethane, and is typical for small organic compounds in a rubbery material. 相似文献
72.
The first part of the paper deals with a critical discussion of the methodical basis of essential work of fracture (EWF) concept with respect to the specimen geometry (especially the notch depth) and application to polymers. In the second part, an in situ testing device, which combines a tensile testing machine with an optical strain-field measuring system, has successfully demonstrated possibility of characterization of fracture behaviour of polystyrene-polybutadiene block copolymers and block copolymer/homopolymer blends as examples of nanostructured polymer materials. It has been shown that knowledge of the time evolution of the strain field close to the crack tips leads to a simple verification of the basic precondition for the applicability of the EWF concept, the precondition “plastic zone coalescence-before-stable crack propagation”. 相似文献
73.
Paul W. Chun 《International journal of quantum chemistry》2001,85(6):697-712
This communication will demonstrate the existence of a thermodynamic molecular switch in the pairwise, sequence‐specific hydrophobic interaction of Ile–Ile, Leu–Ile, Val–Leu, or Ala–Leu over the temperature range of 273–333 K reported by Nemethy and Scheraga in 1962. Based on Chun's development of the Planck–Benzinger methodology, the change in inherent chemical bond energy at 0 K, ΔH°(T0), is 3.0 kcal mol?1 for Ile–Ile, 2.4 for Leu–Ile, 1.8 for Val–Leu, and 1.2 kcal mol?1 for Ala–Leu. The value of ΔH°(T0) decreases as the length of the hydrophobic side chain decreases. It is clear that the strength and stability of the hydrophobic interaction is determined by the packing density of the side chains, with Ala–Leu being the most stable. At 〈Tm〉, the thermal agitation energy, $\int^{T}_{0}\Delta Cp^{\circ}(T)\,dT$, is about five times greater than ΔH°(T0) in each case. Additionally, the thermal agitation energy for the same series, evaluated at 〈Tm〉, decreases in the same order, that is, as the length of the side chain decreases. This pairwise, sequence‐specific hydrophobic interaction is highly similar in its thermodynamic behavior to that of other biological systems, except that the negative Gibbs free energy change minimum at 〈Ts〉 occurs at a considerably higher temperature, 355 K compared to about 300 K. The melting temperature, 〈Tm〉, is also high, 470 K compared to 343 K in a biological system. The implication is that the negative Gibbs free energy minimum at a well‐defined 〈Ts〉 has it origin in the hydrophobic interactions, which are highly dependent on details of molecular structure. In addition to the four specific dipeptide interactions described, we have shown in our unpublished work the existence of a thermodynamic molecular switch in the interactions of 32 dipeptides wherein a change of sign in ΔCp°(T)reaction leads to a true negative minimum in the Gibbs free energy of reaction, and hence, a maximum in the related Keq. Indeed, all interacting biological systems that we have thus far examined using the Planck–Benzinger approach point to the universality of thermodynamic molecular switches. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
74.
茂锆载体催化剂下的乙烯/辛烯共聚及聚合物的^13C NMR研究 总被引:3,自引:0,他引:3
茂锆载体催化剂下的乙烯/辛烯共聚及聚合物的~(13)CNMR研究刘胜生,于广谦,黄葆同(中国科学院长春应用化学研究所长春130022)关键词茂锆载体催化剂,共聚,序列分布,~(13)CNMR由于茂锆催化剂具有高活性,单一活性中心等特点[1,2],并且能... 相似文献
75.
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77.
Two published procedures for glass capillary column production are applied to produce capillaries for chromatography of polar natural compounds. Soda lime glass capillaries, after leaching with aqueous HCL, are either treated with colloidal silicic acid or with barium carbonate and coated with either Silar 7CP or SE 52. A test mixture as well as polar carbohydrate and peptide mixtures are chromatographed on the different columns and their chromatographic properties are evaluated. Combined capillary gas chromatography-electron impact and chemical ionization mass spectrometry are used for identification of the peptide sequence. 相似文献
78.
Yong Deng Da Cheng Yang Yi Shen Yu Guo Zhong 《中国化学快报》2007,18(1):7-9
Based on the structure-activity relationships and antiangiogenic mechanism of RGD-containing peptides,a series of 5-amino- 1,3-dihydro-1,3-dioxo-2H-isoindole derivatives were synthesized.The structures were characterized by ~1H NMR,MS and elementary analysis.There ability to inhibit angiogenesis were evaluated by chick embryo chorioallantoic membrane assay at 10~(-5) mol/L.Compounds 7a and 7b displayed obvious antiangiogenic activity. 相似文献
79.
80.
投料顺序对动态硫化PP/EPDM性能影响及其机理的研究 总被引:12,自引:0,他引:12
针对PP降解在PP/EPDM动态硫化中对体系产生的不利影响。考察了四种不同投料顺序对PP/EPDM动态硫化物的冲击韧性,加工流动性,交联程度和断面形貌等宏观和微观性能,并进行了不同EPDM含量的动态硫化和非硫化PP/EPDM的性能比较。结果表明,优化投料顺序能实现对动态硫化体系中化学反应对象和化学反应程度的有效干预。 相似文献