变温红外光谱研究多嵌段聚氨脂脲的微相分离行为

用傅里叶变换红外光谱方法研究了热处理对由聚环氧丙烷聚醚多元醇、３．５－二乙基甲苯二胺和４，４－二苯基甲烷二异氰酸酯组成的多嵌段聚氨酯脲（ＳＰＵＵ）的微相分离行为的影响．从室温逐步升温到３１０℃的过程中，氨基甲酸酯键（ＵＴ）之间形成的氢键大量解离，而脲键（ＵＡ）之间形成的、具有平面状双分叉结构的氢键在１３０～２００℃范围却大量生成；从３１０℃缓慢冷却到室温后，部分游离的ＵＴ重新形成氢键，而硬段之间形成的ＵＡ氢键的含量又有所增加．结果表明：高温热处理可以有效地提高ＳＰＵＵ的微相分离程度．     

Synthesis and Structure of a 1,3-alternate-Thiacalix[4]arene diamide Derivative

A novel receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. The tetrathiacalix[4]arene diamide shows strong intramolecular hydrogen bonding. The binding behavior towards K⁺ and halides has been examined by ¹H NMR titration experiments.     

Indium(I) bromide-mediated coupling of dibromoacetonitrile with aldehydes followed by Boord elimination of bromine and oxygen of β-bromo alkoxides for preparation of 3-organyl-2-alkenenitriles

The organoindium compound derived from indium monobromide and dibromoacetonitrile reacts with carbonyl compounds to afford the corresponding 2-bromo-2-cyano-indium(III) alkoxide. The action of a second equivalent of indium monobromide onto the alkoxides derived from aldehydes promotes the Boord elimination of the β-related oxygen and bromine atoms leading to 2-alkenenitriles.     

Kinetics and mechanism of azidomercuration of alkenes,cycloalkenes, and their derivatives with a mercuric acetate-sodium azide system

The kinetics of azidomercuration of alkenes, cycioalkenes, and their derivatives with a Hg(OAc)₂-NaN₃ system (1 1, 1 2, and 1 3) was studied. Based on the data on the product structure and kinetic results, it was concluded that HgOAcN₃ and Hg(N₃)₂ play the role of azidomercuration reagents. The reactions with alkenes having a strained double bond occur by a concerted scheme. With nonstrained alkenes, a multistep mechanism is realized, its first reversible step involving the formation of a mercurinium intermediate with an ion pair structure.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No.12, pp. 2479–2485, December, 1995.     

Study of chemical bonds in a-B/C:H films by electron probe microanalysis

This paper describes the study of chemical bonds in amorphous hydrogen rich boron/carbon (a-B/C:H) films by electron probe microanalysis. The films were deposited on Si single crystals by plasma chemical vapour deposition with a precursor-carborane (C₂B₁₀H₁₂) in a laboratory setup. A film thickness and B/C ratio up to a value of 8000 Å and 4, respectively, have been obtained. The analysis of boron and carbon X-ray emission spectra has shown that the nearest order in the films is characterized by the coexistence of C-C, B-C and B-B bonds for B/C 1 and of B-B and B-C bonds for B/C 4. After two years exposure in air the oxygen content in the films increases from 2–5 to 15–20 at.%.     

An Electrostatic Bond Energy Model for Enthalpies of Formation of Chloroalkanes in Gaseous States

An electrostatic bond energy model is formulated to fit the enthalpies of formation and dipole moments of the alkanes and chloroalkanes. In this model, the charge distributions are calculated by an electrostatic approach similar to the "MSE" method, and the enthalpy of formation of a molecule is the sum of the bond energy terms plus the electrostatic energy of the interactions between the charges on all atoms. All parameters of this model are obtained by parameterization. The calculated dipole moments for 13 chloroalkanes and enthalpies of formation for 19 alkanes and non-geminal chloroalkanes agree with the determined values very well. To calculate the enthalpies of formation of geminal chloroalkanes, a correction mainly attributed to the van der Waals interactions in the geminal substituted group, about 24 kJ/mol per pair of geminal chlorine atoms, is introduced.     

Cellular automata approach to site percolation on ℤ2. A numerical study

We present a cellular automata model as a new approach to Bernoulli site percolation on the square lattice. A new macroscopic quantity is defined and numerically computed at each level step of the automata dynamics. Its limit manifests a critical behavior at a value of the site occupancy probability quite close to those obtained for site percolation on ² with the best-known numerical methods.     

Aryl-bis(triorganylphosphine)nickel phenoxides

Compounds of general formulatrans-ArNi(PR₃)₂OAr' (R = Et, cyclohexyl; Ar = 2-MeC₆H₄, 2-FC₆H₄; Ar' = 4-FC₆H₄, 4-NO₂C₆H₄) were synthesized by the reaction of Ar'OK with cationic nickel complexes generated by treatment of ArNi(PR₃)₂Cl with TlBF₄. Syntheses of 4-fluorophenoxide complexes, ArNi(PR₃)₂OC₆H₄F-4, additionally give some quantities oftrans-[ArNi(PR₃)₂OC₆H₄F-4][HOC₆H₄F-4] adducts. Exchange reactions MeC₆H₄Ni(PEt₃)₂OC₆H₄F-4 + XC₆H₄OH 2-MeC₆H₄Ni(PEt₃)₂OC₆H₄X + 4-FC₆H₄OH were studied in THF. The equilibrium is shifted to the right as the acidity of ArOH increases. A linear relationship between lgK _eq and pK _a of XC₆H₄OH in DMSO was found. A conclusion concerning the strong polarization of the Ni-O bond was made on the basis of an analysis of the chemical shifts of fluorine atoms in 2-MeC₆H₄Ni(PEt₃)₂OC₆H₄F-4.Translated fromIvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2266–2271, November, 1995.     

Bonding of the chain structure for novel boranes B3k+pH−5k+p+3

The molecular orbitals obtained from conventional quantum chemistry calculations, are expressed in terms of symmetrized valence bond functions of fragment, and a direct picture of chemical bonding can be drawn easily. This method is utilized, together with extended Huckel calculations, to interpret the bonding properties of a centipede-like chain structure for novel laser-producing boranes B_3k+pH^?_5k+p+3 which is constructed from the repeated unit B₃H₅ halted to each other by three B—H—B bonds.     

A simple method for the characterization of OHO-hydrogen bonds by H-solid state NMR spectroscopy

A set of OHO hydrogen bonded systems with known neutron diffraction structure has been studied by fast ¹H-MAS echo spectroscopy. It is shown that the application of a simple rotor synchronized echo sequence combined with fast MAS allows a faithful determination of the chemical shift of the proton in the hydrogen bond. Employing the empirical valence bond order model, the experimental ¹H chemical shifts of the hydrogen bonded protons are correlated to the hydrogen bond geometries. The resulting correlation between the proton chemical shift and the deviation of the proton from the center of the hydrogen bond covers a broad range of substances. Deviations from the correlation curve, which are observed in certain systems with strong hydrogen bonds, are explained in terms of proton tautomerism or delocalization in low-barrier hydrogen bonds. These deviations are a highly diagnostic tool to select potential candidates for further experimental and theoretical studies. Thus, the combination of the ¹H-MAS echo sequence with the correlation curve yields a simple and versatile tool for the structural analysis of OHO hydrogen bonds.