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921.
L. G. Pinaeva P. S. Sai Prasad B. S. Balzhinimaev V. I. Zaikovskii A. A. Ivanov 《Reaction Kinetics and Catalysis Letters》1988,36(1):229-234
It has been established that fast relaxations are due to catalytic conversion and slow ones are due to the formation of structures with decreasing activity and selectivity.
, , — , .相似文献
922.
Bhanu Nandan L. D. Kandpal G. N. Mathur 《Journal of Polymer Science.Polymer Physics》2002,40(14):1407-1424
The compatibility behavior of polyetherether ketone (PEEK) with poly(ether sulfone) (PES) has been reexamined using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and extrudate swell measurements. The blends were prepared by both melt‐blending and solution‐blending techniques. The phase behavior of blends is strongly affected by the blending technique used. Blends prepared by solution‐blending are compatible in the entire composition range on the basis of the single composition‐dependent glass transitions and exhibit lower critical solution temperature (LCST) behavior. LCST was near 340 °C around which the crystalline melting point of PEEK exists. Near LCST melting‐induced movement of molecular chains disturbs the initial homogeneous state of the solution blends and leads to a phase‐separated state that is thermodynamically more stable in the absence of strong specific interactions between the homopolymers. Contrary to the solution‐blended samples, melt‐blended samples were in the phase‐separated state even at a lower processing temperature of 300 °C. Two glass transitions corresponding to a PEEK‐rich and a PES‐rich phase were found for all compositions. From the measured glass transition of phase‐separated blends, weight fractions of PES and PEEK dissolved in each phase were determined using the Fox equation. Compatibility is greater in the PEEK‐rich compositions than in the PES‐rich compositions. PEEK dissolves more in PES‐rich phases than does PES in the PEEK‐rich phase. Variation of the specific heat increment (ΔCp) at the glass transition with composition also supports these inferences. Solution‐blended samples, quenched from 380 °C, also indicated similar behavior but were slightly more compatible. The aforementioned results are consistent with those inferred from SEM studies and extrudate swell measurements that show a greater compatibility in PEEK‐rich compositions than in PES‐rich compositions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1407–1424, 2002 相似文献
923.
Five simple, rapid and sensitive spectrophotometric procedures for the determination of muzolimine in bulk samples and pharmaceutical dosage forms are described. The methods are based on the formation of coloured species when muzolimine is reacted with 3-methyl-2-benzothiazolinone hydrazone hydrochloride, p-N,N-dimethylphenylenediamine dihydrochloride or p-N-methylaminophenol sulphate and a suitable oxidant or with 2,6-dichloroquinone chlorimide. The results obtained are reproducible with a coefficient of variation of less than 1.5%. 相似文献
924.
Sankar Prasad Bhattacharyya 《Journal of Chemical Sciences》1980,89(2):183-192
The method of calculating CNDO bonding parameters developed recently is extended to transition metal atoms. It is shown that
one of the approximations introduced earlier can also be deduced by a more complete treatment of the imbalance problem in
CNDO-MO theory. The conventionally calibrated bonding parameters indirectly incorporate important contributions from two-particle
interactions. The parameters developed are used to compute the coefficients of metal-to-ligand transfer of spin in many hexafluro
metallate ions of transition metals. The results are compared with those obtained by conventional CNDO-MO calculation. Comparison
of the computed bonding parameters with other available values is also made. 相似文献
925.
William L. Harrison Feng Wang Jeffery B. Mecham Vinayak A. Bhanu Melinda Hill Yu Seung Kim James E. McGrath 《Journal of polymer science. Part A, Polymer chemistry》2003,41(14):2264-2276
New sulfonated poly(arylene ether sulfone) copolymers with high molecular weights were successfully synthesized with controlled degrees of disulfonation of up to 70 mol % via the direct copolymerization of sulfonated aromatic dihalides, aromatic dihalides, and one of four structurally distinct bisphenols. The disodium salts of the 3,3′‐disulfonated‐4,4′‐dichlorodiphenyl sulfone and 3,3′‐disulfonated‐4,4′‐difluorodiphenyl sulfone comonomers were synthesized via the sulfonation of 4,4′‐dichlorodiphenyl sulfone or 4,4′‐difluorodiphenyl sulfone with 30% fuming sulfuric acid at 110 °C. Four bisphenols (4,4′‐bisphenol A, 4,4′‐bisphenol AF, 4,4′‐biphenol, and hydroquinone) were investigated for the syntheses of novel copolymers with controlled degrees of sulfonation. The composition and incorporation of the sulfonated repeat unit into the copolymers were confirmed by 1H NMR and Fourier transform infrared spectroscopy. Solubility tests on the sulfonated copolymers confirmed that no crosslinking and probably no branching occurred during the copolymerizations. Tough, ductile films were solvent‐cast that exhibited increased water absorption with increasing degrees of sulfonation. These copolymers are promising candidates for high temperature proton‐exchange membranes in fuel cells, which will be reported separately in part II of this series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2264–2276, 2003 相似文献
926.
S. Krishna Prasad Yoji Maeda Shankar D. S. Rao Anitha S. Nagamani Uma S. Hiremath C. V. Yelamaggad 《Liquid crystals》2003,30(11):1277-1283
The phase behaviour of two achiral bent core banana-shaped compounds, the hexyloxy (compound I) and decyloxy (compound II) members of the 1,3-phenylene bis[N-(2-hydroxy-4-n-alkoxybenzylidene)-4'-aminobenzoate] series was investigated under hydrostatic pressures up to 300 MPa using high pressure differential thermal analysis and light transmission methods. The reversible transition sequence crystal (Cr1)-B1 phase-isotropic liquid (I), observed at room pressure for compound I, remains in the pressure region up to c 70 MPa. At higher pressures a pressure-induced crystalline phase (Cri) appears between the Cr1 and B1 phases, its temperature region becoming wider with increasing pressure. The temperature vs. pressure phase diagram shows a triple point of 72.9 MPa and 160.3°C for the Cr1, Cri and B1 phases, indicating the lower limit of pressure for the Cri phase. In compound II the reversible transition sequence crystal (Cr1)-B2 phase-I is seen over the whole pressure region, and the temperature range of the B2 phase remains unaltered. It is concluded that both the B1 and B2 banana phases are stable over the whole pressure region studied. 相似文献
927.
928.
929.
David D. Xu George T. Lee Xinglong Jiang Kapa Prasad Oljan Repic Thomas J. Blacklock 《Journal of heterocyclic chemistry》2005,42(1):131-135
A general synthesis of 1,3‐diaryl‐4‐pyrazoleacetic acid esters has been realized via the condensation of a γ‐carboxy ester hydrazone with the Vilsmeier reagent. 相似文献
930.