高聚合度Ⅱ-型聚磷酸铵的合成

用聚合反应-热处理两段工艺合成了高聚合度的聚磷酸铵（APP）阻燃材料,其结构经XRD,粒度及平均聚合度表征。优化反应条件为：磷酸氢二铵1mol,n（磷酸氢二铵）：n（五氧化二磷）：n（脲）：1．0：1．0：0．3．干燥氨气氛下于290℃反应30min,再经250℃-280℃后处理100min-110min。APP的平均聚合度大于150,粒度小于50μm。     

A general scheme for the derivation of evolution equations describing mixed nonlinearity

We examine hyperbolic, quasilinear systems in which the usual quadratic nonlinearity coefficient may be positive or negative depending on the undisturbed state of the medium. A general multiple-scales technique is developed which is capable of determining the evolution equations governing small disturbances to a state which lies close to that where the quadratic nonlinearity coefficient vanishes. The resultant equation contains both quadratic and cubic nonlinearity and describes the mixed nonlinearity inherent in such systems. Extensions to weakly dissipative or weakly dispersive systems are provided as are examples illustrating applications to electromagnetics and solid and fluid mechanics.     

Velocity reversal and the arrows of time

Agendanken experiment is proposed for distinguishing between two models accounting for the macroscopic arrow of time. The experiment involves the veloeity revesal of components of an isolated system, and the two models give contrasting predictions as to its behavior.     

Measurement of the magnetic formfactor of the deuteron forQ 2=0.5 to 1.3 (GeV/c)2 by a coincidence experiment

Elastic electron deuteron scattering was measured at the Bonn 2.5 GeV Electron-Synchrotron using a two spectrometer coincidence technique. Data were taken at values of the four momentum transfer squaredQ ²=0.50, 0.60, 0.78, 1.00, and 1.3 (GeV/c)² at electron scattering angles θ _e =77.5° to 139.0° in order to separate the magnetic dipole formfactorF _M (Q ²) from the electric formfactorF _E (Q ²). Experimental cross sections are compared to theoretical predictions and to measurements of other laboratories. The results indicate that contributions from meson exchange currents are not negligible in thisQ ² region.     

MIDI! basis set for silicon, bromine, and iodine

The MIDI! basis set is extended to three new atoms: silicon, bromine, and iodine. The basis functions for these heteroatoms are developed from the standard 3-21G basis set by adding one Gaussian-type d subshell to each Si, Br, or I atom. The exponents of the d functions are optimized to minimize errors in the geometries and charge distributions that these basis functions yield when they are used in Hartree-Fock calculations with all atoms represented by the MIDI! basis. The MIDI! basis is defined to use five spherical d functions in a d subshell. We present a detailed comparison of such calculations to calculations employing six Cartesian d functions in each d subshell; these studies show that 5D and 6D options give very similar results for molecular geometries and dipole moments, not only for compounds containing Si, Br, and I but also for compounds containing N, O, F, P, S, and Cl. The MIDI! basis set is also tested successfully for hypervalent Si compounds. Received: 7 January 1998 / Accepted: 7 January 1998     

A Readily Accessible Class of Chiral Cp Ligands and their Application in RuII‐Catalyzed Enantioselective Syntheses of Dihydrobenzoindoles

Chiral cyclopentadienyl (Cp^x) ligands have a large application potential in enantioselective transition‐metal catalysis. However, the development of concise and practical routes to such ligands remains in its infancy. We present a convenient and efficient two‐step synthesis of a novel class of chiral Cp^x ligands with tunable steric properties that can be readily used for complexation, giving Cp^xRh^I, Cp^xIr^I, and Cp^xRu^II complexes. The potential of this ligand class is demonstrated with the latter in the enantioselective cyclization of azabenzonorbornadienes with alkynes, affording dihydrobenzoindoles in up to 98:2 e.r., significantly outperforming existing binaphthyl‐derived Cp^x ligands.