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排序方式: 共有308条查询结果,搜索用时 15 毫秒
1.
Sunit S. Dixit A. B. Deshpande S. L. Kapur 《Journal of polymer science. Part A, Polymer chemistry》1970,8(5):1289-1297
Methyl methacrylate was polymerized at 40°C with the VCl4–AlEt3 catalyst system in n-hexane. The rate of polymerization was proportional to the catalyst and monomer concentration at Al/V ratio of 2, indicating a coordinate anionic mechanism of polymerization. NMR spectra were further used to confirm the mechanism of polymerization and stability of active sites responsible for isotacticity. 相似文献
2.
Sunit S. Dixit A. B. Deshpande S. L. Kapur 《Journal of polymer science. Part A, Polymer chemistry》1971,9(5):1167-1172
The polymerization of acrylonitrile with the homogeneous catalyst system of VCl4–AlEt3 in acetonitrile at 40°C has been investigated. The rate of polymerization is found to be first-order with respect to monomer and inversely proportional to the catalyst concentration. The overall activation energy for this catalyst system is 10.97 kcal/mole. The inverse proportionality of rate of polymerization with the catalyst concentration is attributed to the permanent complex formation between the catalyst complex and acrylonitrile, and a reaction scheme is proposed. 相似文献
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4.
A rapid, selective, and sensitive method is described for the purification and analysis of fluoxetine and norfluoxetine using a solid-phase extraction column and gas chromatography-electron-capture detection. Linear quantitative response curves for fluoxetine and norfluoxetine are generated over a concentration range of 20-200 ng/ml. Overall extraction efficiency of the extraction procedure is found to be greater than 90% and greater than 75% with correlation coefficients of 0.997 and 0.993 for fluoxetine and norfluoxetine, respectively. 相似文献
5.
The photodissociation of O(2) in the region from 120-133 nm has been investigated using product imaging. The spectrum in this region is dominated by transitions from the ground state to the first three vibrational levels of the E (3)Sigma(u) (-) state. The O((1)D)+O((3)P) channel is the only product channel observed by product imaging for dissociation at either 124.4 nm or 120.4 nm. The O((1)D(2)) product is aligned in the molecular frame in such a way that its J vector is perpendicular to the relative velocity vector between the O((1)D) and the O((3)P). The variation in the anisotropy of dissociation is approximately predicted by considering transitions on individual lines and then taking into account the coherent excitation of overlapping resonances. At 132.7 nm, both the O((1)D)+O((3)P) and the O((3)P)+O((3)P) channels are observed with branching ratios of 0.40+/-0.08 and 0.60+/-0.09, respectively. At 130.2 nm, the quantum yield for production of O((1)D) is 0.76+/-0.28. 相似文献
6.
Norman G. Gaylord Achyut B. Deshpande Sunit S. Dixit Sukumar Maiti Birendra K. Patnaik 《Journal of polymer science. Part A, Polymer chemistry》1975,13(2):467-482
α-Methylstyrene (MS) and isobutyl vinyl ether (VE) readily polymerize, styrene (S) polymerizes to a small extent, and isobutylene (IB), butadiene (BD), and isoprene (IP) fail to polymerize in the presence of catalytic amounts of AlCl3 when propionitrile, ethyl propionate, and methyl isobutyrate are used as reaction media. MS polymerizes readily and S polymerizes with difficulty in the presence of AlCl3 to yield homopolymers when acrylonitrile (AN) is present and copolymers with ethyl acrylate (EA) and methyl methacrylate (MMA). VE readily homopolymerizes, while IB, BD, and IP fail to polymerize in the presence of AlCl3 and the acrylic monomers. VE readily homopolymerizes, S and MS polymerize to a very small extent, and IB, BD, and IP do not polymerize in the presence of ethylaluminum sesquichloride (EASC) in polar solvents. VE readily homopolymerizes in the presence of EASC and the acrylic monomers. MS polymerizes to a small extent in the presence of EASC and the acrylic monomers to yield equimolar copolymers with EA and MMA and a mixture of cationic homopolymer and equimolar copolymer with AN. S yields equimolar copolymers in low yield in the presence of EASC and the acrylic monomers. IB, BD, and IP in the presence of EASC do not polymerize to any significant extent when EA is present, form AN-rich copolymers and yield poly(methyl methacrylate) in the presence of MMA. A revised mechanism is presented for the formation of cationic, radical, random, and alternating copolymers as well as alternating copolymer graft copolymers in the copolymerization of donor and acceptor monomers. 相似文献
7.
Dixit AA Lei Y Lee KW Quiñones E Houston PL 《The journal of physical chemistry. A》2005,109(9):1770-1775
Multiphoton excitation and dissociation of SO(2) have been investigated in the wavelength range from 224 to 232 nm. Strong evidence is found for two-photon excitation to the H Rydberg state, followed by dissociation to SO + O and ionization of the SO product by absorption of a third photon. The two-photon excitation is resonantly enhanced via the C (1)B(2) intermediate state, and the two-photon yield spectrum thus bears a strong resemblance to the spectrum of this intermediate. Imaging of the O((3)P(2)), S((1)D(2)), and SO products suggests that, following dissociation of SO(2) from the H state, SO is produced in the A and B electronic states. S((1)D(2)) is produced both from two-photon dissociation of SO(2) to give S((1)D(2)) + O(2) and by single-photon dissociation of SO(+). In the former process, the O(2) is likely formed in all of its lowest three electronic states. 相似文献
8.
Lambert HM Davis EW Tokel O Dixit AA Houston PL 《The Journal of chemical physics》2005,122(17):174304
The photodissociation of N(2)O at wavelengths near 130 nm has been investigated by velocity-mapped product imaging. In all, five dissociation channels have been detected, leading to the following products: O((1)S)+N(2)(X (1)Sigma), N((2)D)+NO(X (2)Pi), N((2)P)+NO(X (2)Pi), O((3)P) + N(2)(A (3)Sigma(+) (u)), and O((3)P) + N(2)(B (3)Pi(g)). The most significant channel is to the products O((1)S) + N(2)(X(1)Sigma), with strong vibrational excitation in the N(2). The O((3)P) + N(2)(A,B):N((2)D,(2)P) + NO branching ratio is measured to be 1.4 +/- 0.5, while the N(2)(A) + O((3)P(J)):N(2)(B) + O((3)P(J)) branching ratio is determined to be 0.84+/-0.09. The spin-orbit distributions for the O((3)P(J)), N((2)P(J)), and N((2)D(J)) products were also determined. The angular distributions of the products are in qualitative agreement with excitation to the N(2)O(D (1)Sigma(+)) state, with participation as well by the (3)Pi(v) state. 相似文献
9.
10.
Potentiometric investigations on metal complexes of various bivalent metal ions, viz. UO2(II), Cu(II), Ni(II), Co(II), Cd(II), Pb(II), Zn(II) and Mn(II) with benzilmonol(lepidy!)hydrazone (BLH) have been carried
out at different ionic strengths and at different temperatures in order to determine stability constants of the complexes.
Thermodynamic parameters ΔC, ΔH and ΔS have also been evaluated from temperature coefficient data. The effect of varying the
dielectric constant of the medium on the stability constants of complexes has also been investigated at 30±0.5°C and μ = 0.1MNaCl.
Thermodynamic stability constants and thermodynamic stabilization energies for the first transition metals have also been
discussed. 相似文献