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11.
Indrajit Kar B. M. Mandal S. R. Palit 《Journal of polymer science. Part A, Polymer chemistry》1969,7(10):2829-2836
Chain transfer constants of some fluoroalcohols [HCF2(CF2)n?1CH2OH, n = 2, 4, 6] in the catalyzed polymerization of vinyl acetate, styrene, acrylonitrile, and methyl methacrylate at 60°C have been evaluated by a method based on degree of polymerization. Since fluoroalcohols are normally nonsolvents for polymers, a homogeneous reaction phase is maintained by carrying out the polymerization in benzene (except in case of acrylonitrile, where no solvent was used). The transfer constants vary, depending on the reactivity as well as the polarity of the radicals, in the following order: vinyl acetate > styrene > methyl methacrylate > acrylonitrile. Of the three fluoroalcohols studied, the transfer constants increase with the increasing value of n. The results have been interpreted in terms of polar structure contribution in the transition state of the transfer reactions. 相似文献
12.
Summary The lead ion selective electrode (ISE) consisting of PbS-Ag2S is normally used with a membrane surface of outer layer areaA
o) and inner layer area (A
i) at unity (A
o=A
i). Partial covering of one surface area with an insulating material and keeping the other surface layer intact resulted in different ratios of membrane surface areas exposed to lead solutions. The potential linearly increased with increasing theA
o/A
i ratio and decreased with decreasing theA
o/A
i ratio. The lead ISE potential increased linearly with increasing the membrane thickness, but which required much longer time for a stable potential.
Wirkung von Oberflächenverhältnis und Dicke der Elektrodenmembran auf das Potential einer Bleielektrode
Zusammenfassung Die aus PbS-Ag2S bestehende spezifische Bleiionen-Elektrode wird üblicherweise mit einem Oberflächenverhältnis der Außenfläche (A o) und der Innenfläche (A i) mitA o=A i verwendet. Durch teilweise Abdeckung einer Oberfläche mit isolierendem Material, ohne daß die andere Oberfläche verändert wird, ergaben sich verschiedene Verhältnisse der mit der Bleilösung in Berührung stehenden Oberflächen. Mit dem VerhältnisA o/A i stieg das Potential linear an bzw. es fiel mit diesem Verhältnis ab. Das Potential der spezifischen Bleielektrode stieg mit der Dicke der Membran, stabilisierte sich aber wesentlich langsamer.相似文献
13.
Harrop TC Olmstead MM Mascharak PK 《Journal of the American Chemical Society》2004,126(45):14714-14715
The Ni(II)-dicarboxamido-dithiolato complexes (Et4N)2[Ni(NpPepS)] (1) and (Et4N)2[Ni(PhPepS)] (2) were used as Nid metallosynthons in the construction of higher nuclearity dinuclear Ni-Cu and Ni-Ni species to model the bimetallic Mp-Nid site of the A-cluster of acetyl coenzyme A synthase/CO dehydrogenase (ACS/CODH). Reaction of 1 with [Cu(neo)Cl] and [Ni(terpy)Cl2] in MeCN affords the dinuclear complexes (Et4N)[Cu(neo)Ni(NpPepS)] (3) and [Ni(terpy)Ni(NpPepS)] (4), respectively. Reaction of 2 with [Ni(dppe)Cl2] in MeCN yields [Ni(dppe)Ni(PhPepS)] (6). The Ni-Cu complex 3 exhibits no redox chemistry at the Nid site and no reaction with CO. In contrast, the Nip sites in 4 and 6 are readily reduced (characterized by their Ni(I) EPR spectra) and bind CO, exhibiting nuco bands at 2044 and 1997 cm-1, respectively, indicating terminal CO binding. The present Ni-Ni systems replicate the structural and chemical properties of the A-cluster site in ACS/CODH and support the presence of Ni at Mp in the catalytically active enzyme. 相似文献
14.
Pradip N. Ghosh 《Journal of Molecular Structure》1975,26(2):343-346
A simple theory of linear lattice is applied to the hydrogen bonded linear chain system of HCN to calculate the intermolecular force constants at different temperatures in the condensed phase. The strong CN bond is assumed to remain unperturbed in the hydrogen bond formation. The sharp change in intermolecular force constant while passing from the crystalline to the liquid phase is interpreted as a characteristic of this phase transition (fusion). 相似文献
15.
Pradip K. Bhowmik Robert W. Lenz 《Journal of polymer science. Part A, Polymer chemistry》1993,31(8):2115-2122
A series of fully aromatic thermotropic polyesters based on mono-, di-, and tetra-substituted biphenols was prepared by the melt polycondensation method and examined for their thermotropic behavior by a variety of experimental techniques. The homopolyesters obtained from substituted biphenols containing either one phenyl or two phenyl groups as substituent(s) and TA formed nematic melts, but the homopolymers of the substituted biphenols containing either four sec-butyl groups or two tert-butyl groups with TA had melting transitions, Tm, above 400°C. Thus, it was not possible to determine whether they formed nematic melts. On copolymerization with 30 mol % HBA most of the resulting copolyesters had much lower Tm values, compared to those of respective homopolyesters, and the copolymers of the biphenol monomer containing the tert-butyl groups formed a nematic melt at an observable temperature. However, the copolymer of the biphenol with sec-butyl groups still had a Tm above 400°C. © 1993 John Wiley & Sons, Inc. 相似文献
16.
17.
18.
We look at some one-dimensional semi-infinite superlattices with an underlying Hamiltonian that is of the nearest neighbour, tight binding type. A real space rescaling procedure which is exact in one dimension is applied to obtain the location of the subbands. It has been found that these subbands never overlap in 1D, and we interpret this as a band repulsion effect. Relevance in the case of a disordered system where this band repulsion crosses over to the well-known level repulsion is discussed. Then with a proper matching at the boundary we solve for the sets of denumerably infinite number of decaying solutions (the surface states) in the gaps. These types of states have been proposed quite some time ago. We look at detail theirexact analytical solutions in 1D and find that their decay lengths near the band edges diverge as |E–E
b|–v, wherev=1/2 andE
b is the nearest band edge. The decay lengths and their divergence exponent match extremely well with those obtained from transfer matrix method. Some recent experiments on quantum well structures seem to have observed such states. 相似文献
19.
Controlled synthesis and photoluminescence properties of ZnS nanowires and nanoribbons 总被引:2,自引:0,他引:2
Rapid synthesis of wurtzite ZnS nanowires and nanoribbons has been achieved by a simple thermal evaporation of ZnS powder onto Si substrate in the presence of Au catalyst. A vapor-liquid-solid process is proposed for the formation of the ZnS nanostructures. The flow rate of the inert carrier Ar gas along with the temperature play an important role in defining the morphology of the ZnS nanostructures. The morphological change of the ZnS nanostructures and their growth sequence were studied through scanning electron microscopy. Room-temperature photoluminescence measurements showed intense blue emission at approximately 398 nm from both the nanowires and the nanoribbons. 相似文献
20.
Localized molecular orbitals, two- and three-center bond indices of 1,5-dicarba-closo-pentaborane ( 5 ) and 1,5-dicarba-closo-pentaborane ( 3 ) and their hydrocarbon analogs bicyclo [1,1,1]-pentane and [1,1,1] propellane, respectively, have been calculated using a suitable basis set. No previously reported three-center CBC bond has been found. However, a new three-center BCB bond has been observed in 1,5-dicarba-closo-pentaborane ( 5 ). © 1995 John Wiley & Sons, Inc. 相似文献