A study of the curing process of compounds based on an epoxy oligomer ED-20 and metaphenylene diamine

The possibility of application of different mathematical models used to describe the dependence of viscosity and conversion on the curing time, as well as the rheokinetics of curing of an epoxyamine compound, is considered. It is shown that viscosity growth in the process of curing is determined by the degree of conversion and temperature.     

Polylithiumorganic compounds. Part 29: C,C Bond cleavage of phenyl substituted and strained carbocycles using lithium metal

The reaction of phenyl substituted cyclopropanes phenylcyclopropane and 1,1-diphenylcyclopropane, phenyl substituted bicyclobutanes 1-phenylbicyclobutane, 1-methyl-3-phenylbicyclobutane, 1-methyl-2,2-diphenylbicyclobutane, as well as phenyl substituted spiropentanes phenylspiropentane and 1,1-diphenylspiropentane with lithium metal or lithium di-t-butylbiphenyl (LiDBB) was investigated. Under suitable reaction conditions and choice of solvent in all cases cleavage of the single bond next to the activating phenyl group was observed. The dilithiumorganic compounds thus obtained are sufficiently stable and can be trapped with electrophiles. Lithium hydride elimination is observed as follow-up reaction only in a few cases. The corresponding anions of the strained ring systems 1-lithio-2,2-diphenylcyclopropane, 1-lithio-3-phenylbicyclobutane, 1-lithio-3-methyl-2,2-diphenylbicyclobutane, and 1-lithio-4-phenylspiropentane, which can be obtained by lithium bromine exchange or by metalation of the unsubstituted carbocycle, do not show any cleavage upon reaction with lithium metal.     

Application of semiempirical long-range dispersion corrections to periodic systems in density functional theory

Ewald summation is used to apply semiempirical long-range dispersion corrections (Grimme, J Comput Chem 2006, 27, 1787; 2004, 25, 1463) to periodic systems in density functional theory. Using the parameters determined before for molecules and the Perdew-Burke-Ernzerhof functional, structure parameters and binding energies for solid methane, graphite, and vanadium pentoxide are determined in close agreement with observed values. For methane, a lattice constant a of 580 pm and a sublimation energy of 11 kJ mol(-1) are calculated. For the layered solids graphite and vanadia, the interlayer distances are 320 pm and 450 pm, respectively, whereas the graphite interlayer energy is -5.5 kJ mol(-1) per carbon atom and layer. Only when adding the semiempirical dispersion corrections, realistic values are obtained for the energies of adsorption of C(4) alkenes in microporous silica (-66 to -73 kJ mol(-1)) and the adsorption and chemisorption (alkoxide formation) of isobutene on acidic sites in the micropores of zeolite ferrierite (-78 to -94 kJ mol(-1)). As expected, errors due to missing self-interaction correction as in the energy for the proton transfer from the acidic site to the alkene forming a carbenium ion are not affected by the dispersion term. The adsorption and reaction energies are compared with the results from M?ller-Plesset second-order perturbation theory with basis set extrapolation.     

Dual Complexes of Cubical Subdivisions of ℝ<Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>

We use a distortion to define the dual complex of a cubical subdivision of ℝ ⁿ as an n-dimensional subcomplex of the nerve of the set of n-cubes. Motivated by the topological analysis of high-dimensional digital image data, we consider such subdivisions defined by generalizations of quad- and oct-trees to n dimensions. Assuming the subdivision is balanced, we show that mapping each vertex to the center of the corresponding n-cube gives a geometric realization of the dual complex in ℝ ⁿ .     

Design of circular ARC finline tapers

The aim of this paper is the development of a technological simple procedure for the fabrication of tapers in finline technique with a high transmission and low reflection characteristics. This method employs tapers between rectangular waveguides and finline sections or between two electrically different waveguides in form of circular arcs which are matched to the required lapse of the slot width as a function of the characteristic impedance. The appicability of this method assumes that the transmission properties of the considered finline are known. Several examples show the feasibility of the method.     

Investigation of the residual stresses in the carbamide polymer-glass boundary layer

The residual stresses at the carbamide polymer-glass interface have been investigated for the first time. It has been established that a high residual stress level exists in the polymer-glass boundary layer. Methods of reducing the residual microstress level are indicated.     

Komplexe des Chroms,Molybdäns und Wolframs mit Aminoarsan-Liganden

Complexes of Chromium, Molybdenum, and Tungsten with Aminoarsanes as Ligands The aminoarsanes Me₂As? NMe₂, MeAs(NMe₂)₂, and As(NMe₂)₃ form with the carbonyles of the sub-group VI metals complexes of the general formula (CO)₅M? L (L = aminoarsane; M ? Cr, Mo, W). The cleavage of the As? N bond by reactions with acids HX results in the formation of complexes of the general formula (CO)₅M? As(Me₂)? X, (CO)₅M? As(Me)X₂, and (CO)₅M? AsX₃.     

[La2Cl3(OAc)2(H2O)7]Cl: Das erste Lanthanid-Acetat-Halogenid-Hydrat mit Chlorid in innerer Koordinationssphäre

[La₂Cl₃(OAc)₂(H₂O)₇]Cl: The First Lanthanide-Acetate-Halide-Hydrate with Chloride in Inner-Sphere Coordination [La₂Cl₃(OAc)₂(H₂O)₇]Cl has been obtained as single crystals through the reaction of LaCl₃ · 7H₂O with diluted acetic acid or from La₂O₃ with acetyl chloride. In the crystal structure (triclinic, Z = 2, P1 (no. 2), a = 919.6(2), b = 950.7(2), c = 1178.9(2) pm, α = 82.52(1), β = 84.14(1), γ = 64.69(1)°, R = 0.021, R_w = 0.020), La³⁺ is surrounded by nine ligands (O, Cl). La1 has two chloride and seven oxygen ligands whereas La2 has one chloride and eight oxygen atoms as nearest neighbours. Four of the oxygen ligands of each lanthanum cation originate from a ?tetradentate”? acetate anion, the others from crystal water molecules. The ?tetradentate”? acetate groups are coordinated not only to one central La³⁺ as chelate ligands, but also to the ?left”? and ?right”? La³⁺ neighbours. Thereby, a one-dimensional infinite cationic chain, [La₂Cl₃(OAc)₂(H₂O)₇]⁺, is formed that runs in the [011] direction. These chains are held together by ?lonesome”? chloride ions which are surrounded by (4 + 1) water molecules and connected to the chains via hydrogen bonds.