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951.
Allison K. O'Brien Neil B. Cramer Christopher N. Bowman 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):2007-2014
The overall effects of oxygen on thiol–acrylate photopolymerizations were characterized. Specially, the choice of thiol monomer chemistry, functionality, and concentration on the extent of oxygen inhibition were considered. As thiol concentration was increased, the degree of oxygen inhibition was greatly reduced because of chain transfer from the peroxy radical to the thiol. When comparing the copolymerization of 1,6‐hexanediol diacrylate with the alkane‐based thiol (1,6‐hexane dithiol) to the copolymerization with the propionate thiol (glycol dimercaptopropionate), it was found that the propionate system was much more reactive and polymerized to a greater extent in the presence of oxygen. In addition, the functionality was considered where the glycol dimercaptopropionate was compared to a tetrafunctional propionate of similar chemistry (pentaerythritol tetrakis(mercaptopropionate)). Given the same thiol concentration, the higher functionality thiol imparted a faster polymerization rate, due to the increased polymer system viscosity, which limited oxygen diffusion and decreased the extent of overall oxygen inhibition. Thus, preliminary insight is provided into how thiol monomer choice affects the extent of oxygen inhibition in thiol–acrylate photopolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2007–2014, 2006 相似文献
952.
K. Madhavan B. S. R. Reddy 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2980-2989
A series of poly(dimethylsiloxane‐urethane) elastomers based on hexamethylenediisocyanate, toluenediisocyanate, or 4,4′‐methylenediphenyldiisocyanate hard segment and polydimethylsiloxane (PDMS) soft segment were synthesized. In this study, a new type of soft‐segmented PDMS crosslinker was synthesized by hydrosilylation reaction of 2‐allyloxyethanol with polyhydromethylsiloxane, using Karstedt's catalyst. The synthesized soft‐segmented crosslinker was characterized by FT‐IR, 1H, and 13C NMR spectroscopic techniques. The mechanical and thermal properties of elastomers were characterized using tensile testing, thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamical mechanical analysis measurements. The molecular structure of poly(dimethylsiloxane‐urethane) membranes was characterized by ATR‐FTIR spectroscopic techniques. Infrared spectra indicated the formation of urethane/urea aggregates and hydrogen bonding between the hard and soft domains. Better mechanical and thermal properties of the elastomers were observed. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft and hard segment domains, resulting in the increase in the glass‐transition temperature of soft segments. DSC analysis indicates the phase separation of the hard and soft domains. The storage modulus (E′) of the elastomers was increasing with increase in the number of urethane connections between the hard and soft segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2980–2989, 2006 相似文献
953.
Siripon Anantawaraskul João B. P. Soares Preechathorn Jirachaithorn Jumras Limtrakul 《Journal of Polymer Science.Polymer Physics》2006,44(19):2749-2759
Four polyethylene samples (PE) with different molecular weight distributions (MWD) were analyzed by crystallization analysis fractionation (Crystaf) at several cooling rates to investigate the effect of MWD and cooling rate on their Crystaf profiles. Using these results, we developed a mathematical model for Crystaf that considers crystallization kinetic effects, which are ignored in all previous Crystaf models. The Crystaf model we proposed can fit the experimental Crystaf profiles of the 4 polyethylene resins very well. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2749–2759, 2006 相似文献
954.
The kinetics of streptomycin degradation by hydrogen peroxide at pH 7.4 was investigated. The reaction was catalyzed by traces of Cu(II) ions, and it was followed spectrophotometrically at 322 nm by applying the initial-rate method. The kinetic parameters of the reaction are reported, and a rate equation is suggested. From the dependence of the relative rate constants on the temperature, the activation energy was calculated to be 57.5 kJ/mol. Based on this reaction, a kinetic method for streptomycin determination is proposed. The calibration graph is linear in the ranges 1.94 - 15.48 microg/cm(3) and 0.15 - 1.94 microg/cm(3). The influence of foreign ions and molecules on the accuracy of the determinations was investigated. The proposed kinetic method has high selectivity and good sensitivity, and enabled to determine streptomycin in pharmaceutical samples. 相似文献
955.
E. E. Sergeev P. V. Fabinskii B. V. Polyakov V. A. Fedorov 《Russian Journal of Inorganic Chemistry》2006,51(4):687-690
The solubility of acetoacetylferrocene and 1,1′-bis(acetoacetyl)ferrocene in water and aqueous ethanol at various temperatures is studied over a wide solvent composition range. The solubilities of both compounds increase as the temperature or ethanol concentration is raised, particularly in the case of acetoacetylferrocene. The dissolution of both β-diketones is accompanied by positive changes in enthalpy and entropy. 相似文献
956.
M. B. Babanly G. M. Guseinov D. M. Babanly F. M. Sadygov 《Russian Journal of Inorganic Chemistry》2006,51(5):810-813
The polythermal sections TlBr-Tl2S, TlBr-Tl4S3, TlBr-TlS, and Tl6SBr4-Tl; the isothermal section at 300 K of the phase diagram; and the projection of the liquidus surface of the Tl-S-Br system have been investigated in the composition region Tl-TlBr-S by DTA, X-ray powder diffraction analysis, and microhardness measurements. The primary crystallization regions, including that of the only ternary compound (Tl6SBr4), have been determined, and the types and coordinates of the invariant and univariant equilibria in the phase diagram are determined. 相似文献
957.
J.-S. Kang G. Kim S.S. Lee S. Choi S. Cho S.W. Han H.J. Shin B.I. Min 《Journal of magnetism and magnetic materials》2006
The spatial concentration distribution and local electronic structure of ferromagnetic Ge1−xTx (T=Cr, Mn, Fe) DMS single crystals have been investigated by using scanning photoelectron microscopy (SPEM), X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). It is found that doped T ions in Ge1−xTx crystals are chemically phase-separated, suggesting that the observed ferromagnetism arises from the phase-separated T-rich phases in Ge1−xTx. 相似文献
958.
B C Anusionwu 《Pramana》2006,67(2):319-330
The thermodynamic properties of Sb-Sn and In-Sn liquid alloys have been studied using the quasi-chemical model for compound
forming binary alloys and that for simple regular alloys. The concentration fluctuation S
cc(0) and the Warren-Cowley short-range order parameter (α
1) were determined for the whole concentration range at a temperature of 770 K. The surface tensions of these liquid alloys
were determined for the whole concentration range by using energetics determined from thermodynamic calculations. In all calculations,
In-Sn manifested properties very close to alloys of ideal mixing, while Sb-Sn showed properties that are asymmetric about
equiatomic composition. Our results suggest that a weak complex of the form SbSn2 could be present in the Sb-Sn alloy at a temperature of about 770 K. 相似文献
959.
J. Pal C. C. Dey S. Bose B. K. Sinha M. B. Chatterjee D. P. Mahapatra 《Zeitschrift für Physik A Hadrons and Nuclei》1987,356(3):281-286
The analogue of the 0+ ground state in 118Sn has been observed in the compound nucleus 118Sb through 117Sn(p,n γ) 117Sb reaction. The neutron decays of this analogue resonance have been studied from the deexciting γ-rays of the residual nucleus 117Sb. From off resonance excitation functions, spin assignments have been made to states in 117Sb, on the basis of Hauser-Feshbach formalism. The resonance parameters of the isobaric analogue resonance have been determined, including the total, proton and neutron decay widths. 相似文献
960.
S. Ebel B. Reyer und A. Werner-Busse 《Fresenius' Journal of Analytical Chemistry》1987,327(2):193-197
Summary This paper describes a reliable working station for the in line-process control in chemical plants. Essential parts of the equipment (pump, column) are in duplicates and may be combined by computer control in different lines. One pump and column is in working position, the other is held in ready to work position by conditioning. While one column is in working position, the system is able to calibrate the other column and to switch to this column in the case of breakdown of the other column. By means of chromatographic data (as retention time, peak height of standards, data of separation) the working column is under control and the switching to the other column is down before a real breakdown. The status of the detector is followed by number and distance in time of the necessary auto-zero operations and by the noise of the lamp.
Herrn Prof. Dr. W. Fresenius aus Anlaß des 125jährigen Erscheinens der Fresenius Zeitschrift für Analytische Chemie gewidmet 相似文献
Herrn Prof. Dr. W. Fresenius aus Anlaß des 125jährigen Erscheinens der Fresenius Zeitschrift für Analytische Chemie gewidmet 相似文献