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1.
Divinylsiloxane‐bisbenzocyclobutene (DVS‐bisBCB) polymer has very low dielectric constant and dissipation factor, good thermal stability, and high chemical resistance. The fracture toughness of the thermoset polymer is moderate due to its high crosslink density. A thermoplastic elastomer, polystyrene–polybutadiene–polystyrene triblock copolymer, was incorporated into the matrix to enhance its toughness. The cured thermoset matrix showed different morphology when the elastomer was added to the B‐staged prepolymer or when the elastomer was B‐staged with the DVS‐bisBCB monomer. Small and uniformly distributed elastomer domains were detected by transmission electron micrographs (TEM) in the former case, but TEM did not detect a separate domain in the latter case. A high percentage of the polystyrene–polybutadiene–polystyrene triblock copolymer could be incorporated into the DVS‐bisBCB thermoset matrix by B‐staging the triblock copolymer with the BCB monomer. The elastomer increased the fracture toughness of DVS‐bisBCB polymer as indicated by enhanced elongation at break and increased K1c values obtained by the modified edge‐lift‐off test. Elastomer modified DVS‐bisBCB maintained excellent electrical properties, high Tg and good thermal stability, but showed higher coefficient of linear thermal expansion values. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1591–1599, 2006  相似文献   
2.
The reaction of pyridine 1-oxide with 1-adamantanethiol in acetic anhydride produced a mixture of 2- and 3-(1-adamantanethio)pyridines, 1-aeetyl-2-(1-adamantanethio)-3-hydroxy-4-acetoxy-1,2,3,4-telrahydropyridine and the corresponding 3-acetoxyderivative. Pure substances were separated by means of column chromatography on alumina. The tetrahydropyridines were identified by means of their proton magnetic and mass spectra. 4-(1-Adamantanethio)pyridine was synthesized from 4-chloropyridinc and 1-adamantanethiol. The three isomeric (1-adamantanethio)-pyridines were, each, cleaved by concentrated hydrochloric acid to give 1-chloroadamantane and the corresponding pyridinethiol.  相似文献   
3.
Many reactions of transition metal compounds involve a change in spin. These reactions may proceed faster, slower--or at the same rate as--otherwise equivalent processes in which spin is conserved. For example, ligand substitution in [CpMo(Cl)2(PR3)2] is faster than expected, whereas addition of dinitrogen to [Cp*Mo(Cl)(PMe3)2] is slow. Spin-forbidden oxidative addition of ethylene to [Cp*Ir(PMe3)] occurs competitively with ligand association. To explain these observations, we discuss the shape of the different potential energy surfaces (PESs) involved, and the energy of the minimum energy crossing points (MECPs) between them. This computational approach is of great help in understanding the mechanisms of spin-forbidden reactions, provided that accurate calculations can be used to predict the relevant PESs. Density functional theory, especially using gradient-corrected and hybrid functionals, performs reasonably well for the difficult problem of predicting the energy splitting between different spin states of transition metal complexes, although careful calibration is needed.  相似文献   
4.
Summary Interpretive methods are accepted to give the best possible results for selectivity optimization in HPLC. However the methods are very complex, and most work so far has been detailed academic studies. This paper describes an evaluation of a complete integrated system incorporating peak labelling, modelling of retention behaviour and calculation of response surfaces, with particular emphasis on the retention modelling. The peak labelling section has been discussed previously.A piece-wise quadratic function is investigated for the modelling of retention times across an isoeluotropic plane to effect selectivity optimization in HPLC. This requires 10 data-points on the isoeluotropic plane. The predicted global optimum and local optima are evaluated by comparison of calculated and experimental retention data, for a nine component sample. Seven interstitial points, distributed across the whole plane between the data-points, are similarly evaluated for a related sample. The typical error (in retention time) is less than 2%, often 1%, and the maximum error is 4.2%. At the global optimum the error was found be less than 1.3% for all 9 peaks.  相似文献   
5.
6.
A novel non-linear Raman spectroscopic technique, which can be used to characterize the chemical composition of the interface region of volatile aerosol particles, is described. The technique is morphology-dependent stimulated Raman scattering (MDSRS). We discuss the phenomenology behind this new optical probe, and present experimental results which show that this technique can be used as quantitative spectroscopic tool. We outline the potential application of MDSRS to in situ gas—aerosol kinetics and dynamics studies.  相似文献   
7.
Valuable organic compounds such as alpha-hydroxy acids are easily synthesised with relevant selectivity enhancement using a sol-gel hydrophobized nanostructured silica matrix doped with the organocatalyst TEMPO: A materials science based synthetic route which cannot be achieved via classical homogeneous synthesis.  相似文献   
8.
A comparison has been made between the spectroscopic properties of the laser dye rhodamine 6G (R6G) in mesostructured titanium dioxide (TiO(2)) and in ethanol. Steady-state excitation and emission techniques have been used to probe the dye-matrix interactions. We show that the TiO(2)-nanocomposite studied is a good host for R6G, as it allows high dye concentrations, while keeping dye molecules isolated, and preventing aggregation. Our findings have important implications in the context of solid state dye-lasers and microphotonic device applications.  相似文献   
9.
Zhao Z  Russell PJ 《Electrophoresis》2003,24(18):3284-3288
To separate and identify the proteases, a substrate-specific, sensitive assay in sodium dodecyl sulfate (SDS)-polyacrylamide gels after two-dimensional (2-D) electrophoresis has been developed. This method allows simultaneous determination of protease cleavage specificity, molecular weight, isoelectric point, and if necessary, amino acid sequencing. After isoelectric focusing in immobilized pH gradient (IPG) strips (pH 6-11) (first dimension), trypsin was electrophoresed in 12% SDS polyacrylamide gels (second dimension) copolymerized with Boc-Gln-Ala-Arg-MCA (4-methyl-coumaryl-7-amide). The gels were washed in cold 2.5% Triton X-100 and water, and incubated in assay buffer (6.3 mM Bicine, 100 mM NaCl). Trypsin cleavage of the peptide-MCA generated fluorescent 7-amino-4-methyl-coumarin. In 1-D gels, as low as 500 pg trypsin could be detected and trypsin band volumes correlated linearly with the amounts of trypsin (R(2) = 0.999). In 2-D gels, the lowest amount of trypsin detected was 1 ng. The linear regression of spot volume and loading amount was still good (R(2) = 0.974). To optimize renaturation conditions, 5x5 min washes with 2.5% Triton X-100 and water, respectively, gave the strongest band volume. For fluorescence development, an assay buffer at pH 9 was the best; incubation at 37 degrees C for 30 min was sufficient. The method has application for identifying novel proteases as it does not rely on antibodies.  相似文献   
10.
The paper describes a modified "wait-and-see" approach to solving two-stage stochastic programming problems. The approach, which involves a detailed sensitivity analysis in the classical sense, is described within the frameworks of decision theory and probabilistic programming. Although optimality in the mathematical sense cannot be guaranteed by using the approach, it is suggested that the managerial benefits weigh heavily in its favour. The approach allows management to consider a wide variety of objectives in making the choice between alternatives and facilities detection of the cause of any infeasibility due to management policy constraints. In addition, it allows much simpler programming calculations and provides an upper bound on the benefits that can be obtained by solving the full "here-and-now" problem and thus a judgement of the worth of the added computational burden can easily be made.  相似文献   
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