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1.
Jaedong Cho John Blackwell Sergei N. Chvalun Morton Litt Yuan Wang 《Journal of Polymer Science.Polymer Physics》2004,42(13):2576-2585
As‐cast films of poly(2,5‐benzimidazole) exhibit uniplanar orientation in which the planes of the aromatic rings lie parallel to the film surface. Upon doping with phosphoric acid, the original crystalline order is lost, but the doped film can be stretched to produce films with uniaxial orientation. After thermal annealing at 540 °C, nine Bragg reflections are resolved in the fiber diagram, and these are indexed by an orthorhombic unit cell with the dimensions a = 18.1 Å, b = 3.5 Å, and c = 11.4 Å, containing four monomer units of two chains. The absence of odd‐order 00l reflections points to a 21 chain conformation, which is probably planar so that the aromatic units can be stacked along the b axis. The water and phosphoric acid contents of the crystalline structure cannot be determined exactly because of the presence of extensive amorphous regions that probably have different solvation. The best agreement between the observed and calculated intensities is for an idealized structure containing two phosphoric acids and two water molecules per unit cell. However, the phosphoric acid is probably present mainly in the form of pyrophosphoric acid and its higher oligomers. In addition, the X‐ray data are consistent with a more disordered structure containing chains with random (up and down) polarity and a lack of c‐axis registry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2576–2585, 2004 相似文献
2.
A cubic (trivalent) graph is said to be 4-arc-transitive ifits automorphism group acts transitively on the 4-arcs of (wherea 4-arc is a sequence v0, v1, ... v4 of vertices of such thatvi1 is adjacent to vi for 1 i 4, and vi1 vi+1for 1 i < 4). In his investigations into graphs of thissort, Biggs defined a family of groups 4+(am), for m = 3,4,5...,each presented in terms of generators and relations under theadditional assumption that the vertices of a circuit of lengthm are cyclically permuted by some automorphism. In this paperit is shown that whenever m is a proper multiple of 6, the group4+(am) is infinite. The proof is obtained by constructing transitivepermutation representations of arbitrarily large degree. 相似文献
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The mass spectrum of penta acetyl gitoxin is reported and discussed. This cardenolide derivative has recently been the subject of extensive metabolic study. Fragmentation processes are described which account for all of the major ions. High resolution measurements, metastable peaks and mass shifts, for the propionyl derivative, are reported to establish the validity of these proposals. A brief indication of the potential value of this technique, when combined with deuteroacetylation, to metabolic studies in this field is given, along with comments on the spectra of related compounds. 相似文献
5.
Shah BK Neckers DC Shi J Forsythe EW Morton D 《The journal of physical chemistry. A》2005,109(34):7677-7681
Anthanthrene (1) derivatives substituted at the 4,10 and 6,12 positions (2-6) were synthesized as promising candidates for organic light emitting diodes (OLEDs). The emission of these compounds can be manipulated in the blue region (lambda(max) = 437-467 nm) through structural modifications. Photophysical and electrochemical properties (phi(F) = 0.20-0.47; tau(F) = 2.97-6.06 ns; HOMO-LUMO energy gap = 2.25-2.56 eV) as well as geometry optimized structures of 1-6 are reported. 相似文献
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Zhu H Pan S Gu S Bradbury EM Chen X 《Rapid communications in mass spectrometry : RCM》2002,16(22):2115-2123
9.
ESR spectra observed in γ-irradiated CsAsF6 and CsSbF6 matrices have been assigned to the free radicals AsF2?6 and SbF2?6 respectively. The large, isotropic central-atom hyperfine interactions and isotropic g-values of these species suggest that they possess 2Atg ground-states in Oh symmetry. The contribution to the semi-occupied orbital of the central-atom valence s atomic orbital is ≈ 0.6, greater than in the halogen hexafluorides (≈0.4) and the chalcogen hexafluoride anions (≈ 0.5). Variation of the central-atom hyperfine interaction with temperature is interpreted in terms of a second-order Jahn-Teller effect involving a low-lying 2T1u excited state. 相似文献
10.
Shaul M. Aharoni Morton H. Litt 《Journal of polymer science. Part A, Polymer chemistry》1974,12(3):639-650
A polymer, poly(2,5-trimethylene benzimidazole), the first of a new family of nonsymmetrical polymers, was synthesized via an eight-step synthetic route. The polymer, obtained by melt polymerization, is amorphous and in its neutral form behaves as a moderate insulator. It forms 1 : 1 HCl adducts. When cast from formic acid solution, it forms 1 : 1 formic acid adducts. The acid adducts are semiconductors with resistivities in the 106–108 ohm-cm range. Space-charge effects are generated in the adducts as carrier mobility rises. 相似文献