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991.
The degradation mechanism of photocrosslinking products formed by cyclized polyisoprene-diazide system under the influence of the different alkyl benzene sulfonic acids was studied. The effects of alkyl chain length and the concentration of alkyl benzene sulfonic acids on the rate of degradation reaction were discussed. It was found that in the initial stage of degradation, the cyclicity ratio and the average fused ring number did not change considerably, but the percentage of uncyclized parts content varied significantly. The suitable mechanism was supposed. 相似文献
992.
993.
Ante Juki? 《European Polymer Journal》2006,42(5):1105-1112
The miscibility and intermolecular interactions between polystyrene (PS) and poly(ethylene-co-propylene) (EPC), as well as between PS and long-chain poly(alkyl methacrylates) (PAMA), namely, poly(dodecyl methacrylate) (PDDMA) and poly(octadecyl methacrylate) (PODMA), in dilute xylene solutions at 30 °C were studied. Investigated polymers are widely used as rheology modifiers, i.e. viscosity index improvers and pour point depressants for lubricating mineral oils. The specific and reduced viscosities of two- and three-component polymer solutions as well as intrinsic viscosities and Huggins’ parameter values were determined as functions of the polymer mixture composition and overall polymer concentration. The reduced viscosity was found to be linearly dependent on the overall polymer concentration. The observed viscosities of polymer mixtures were intermediate to those of the mixture constituents; the values decrease in the order: EPC > PS > PAMA. The specific viscosities of all the polymer mixtures obtained as the experimental results and calculated applying the Catsiff-Hewett and Krigbaum-Wall theoretical equations were considered. Since all the polymer/polymer pairs showed the negative viscometric interaction parameter values (Δb12 < 0), the PS/EPC and EPC/PAMA mixtures were found to be immiscible. The observed repulsive molecular interactions originate from the differences in polymer composition and molar masses. This conclusion was supported by calculations employing the group contribution approach of Coleman, Graf and Painter. The calculated values of interaction parameters for (co)polymer blends, Λ12, were 5.47, 6.42 and 13.1 J cm−3 for PS/PDDMA, PS/PODMA and PS/EPC, respectively. 相似文献
994.
A. A. Shestopalov L. A. Rodinovskaya A. M. Shestopalov V. P. Litvinov 《Russian Chemical Bulletin》2005,54(4):992-996
Three-component reactions of 4-hydroxycoumarin, carbonyl compounds, and malono-nitrile or alkyl cyanoacetates in ethanol in
the presence of Et3N as a catalyst give substituted 2-amino-5-oxo-4,5-dihydropyrano[3,2-c]chromenes.
Dedicated to Academician V. I. Minkin on the occasion of his 70th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 968–972, April, 2005. 相似文献
995.
The pseudotertiary phase diagram of the microemulsion system alkyl polyglucoside/n-butanol/n-hexane/water was plotted at (30.0±0.1) ℃. The dielectric measurements, including permittivity, conductivity, relaxation strength, characteristic relaxation time, etc,, were applied to investigate the microstructure of the system. Unique dielectric relaxations were observed over the frequency range of 5-10^7 Hz, taking place possibly through an interracial polarization mechanism. According to the results obtained from dielectric spectroscopy, the structures of the microemulsion O/W, BC and W/O were determined, and some dielectric and phase parameters were calculated. 相似文献
996.
The adsorption of codeine from aqueous solution onto colloidal silica and silica surface-modified with chemiadsorbed octadecyl dimethyl silane (ODDMS) or dimethyl silane (DMS) groups was studied in the presence of neutral electrolytes at different pH values. From codeine-hydrochloride solutions codeine cations are strongly bound to negatively charged silica surfaces. Inorganic salts (NaCl, NaNO3) reduce the adsorption of the organic cation. On silica modified by ODDMS (10% of surface silanol groups are occupied), codeine cations are adsorbed to a higher extent at pH 6, while at pH 8 the adsorbed amounts are lower than on the bare silica surface. Neutral electrolytes reduce codeine adsorption on the ODDMS modified silica. On the hydrophobic silica, completely covered by DMS groups, codeine adsorption is considerably lower than on the bare silica, but neutral salts increase the adsorption. The adsorption of codeine is compared with the adsorption of aggregating surfactant ions. Common and different features of their interactions with silica surfaces are outlined. 相似文献
997.
An analytical method consisting of flow injection sampling and chemiluminescence detection for the determination of thyroxine hormone is described. It is based on the weak chemiluminescent reaction of KMnO4 ‐ Na2SO3 in acidic medium, which is enhanced by the addition of thyroxine hormone. The chemiluminescence intensity was correlated linearly with concentration of thyroxine in the range of 1.0 × 10?7 – 2.0 × 10?6 mol L?1 (r2 = 0.9976) with a relative standard deviation (n = 4) in the range of 1.0 – 1.9%. The limit of detection (3σ blank) is 5.0 × 10?9 mol L?1 with a sample throughput of 180 h?1. The method has been applied to the determination of thyroxine in pharmaceutical preparations and the results are in good agreement with the value reported. Metal and non‐metal ions and some organic compounds commonly present in tablets and some amino acids were also studied for thyroxine determination. 相似文献
998.
In an attempt to clarify the origin of the dual phosphorescence in phenyl alkyl ketones, we have made some calculation (within the C.I.P.S.I. method in an excitonic scheme) to elucidate the conformation of both ground states and excited states of propiophenone. Our calculations have shown the presence of two stable isomers in the ground state, first n * state, and first * singlet and triplet states. So our work suggests that the origin of the dual phosphorescence of propiophenone could be related to the conformational change of the molecule in the n * state, because the most stable conformations in the n * state and in the ground state are different. 相似文献
999.
V. Yu. Petukhova Yu. A. Strelenko K. A. Lyssenko N. N. Makhova 《Russian Chemical Bulletin》2007,56(8):1550-1554
A method for the synthesis of 1-[ω-(3,3-dialkyldiaziridin-1-yl)alkyl]-3,3-dialkyldiaziridines based on the reaction of ketoxime
O-arenesulfonates with alkylenediamines was developed. Diastrereomers (the racemic and meso forms) of 1-[2-(3,3-dimethyldiaziridin-1-yl)ethyl]-3,3-dimethyldiaziridine were isolated. The structure of the meso form was confirmed by X-ray diffraction analysis.
Dedicated to Academician V. A. Tartakovsky on his 75th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1491–1495, August, 2007. 相似文献
1000.
U. Goeschel H. Lee D. Y. Yoon R. L. Siemens B. A. Smith W. Volksen 《Colloid and polymer science》1994,272(11):1388-1395
Thin films of rigid poly(p-phenylene pyromellitimide) (PMDA-PDA) and semi-rigid poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the respective poly(amic acid) and poly(amic ethyl ester) precursors, were characterized with respect to their optical, thermomechanical and structural properties. Both polyimides exhibit an unusually large anisotropy between the in-plane and out-of-plane refractive indices, with n ranging from 0.198 to 0.216 for PMDA-PDA and from 0.230 to 0.242 for BPDA-PDA, nearly independent of the nature of the initial polyimide precursor, film thickness, and film preparation method. PMDA-PDA films exhibit low coefficients of thermal expansion (CTE's) of 6.5 and 8.2 ppm/C for the acid-derived and the ester-derived polyimides, respectively. In comparison, the BPDA-PDA films show CTE values of 4.3 and 18.0 for the acid-derived and ester-derived samples, respectively, despite the small differences in their optical anisotropies. Wide-angle x-ray diffraction patterns obtained in reflection and transmission for the various samples reveal a strong in-plane chain orientation for both PMDA-PDA and BPDA-PDA polyimides, with somewhat better intermolecular packing order for the ester-derived polyimide films. These effects of chemical structure and precursor on properties and structures of the polyimide films are discussed in light of recent theoretical considerations of semiflexible polymers.Dedicated to Prof E. W. Fischer on the occasion of his 65th birthday 相似文献