Specific features of tetrahydrofuran copolymerization with lactones

Mechanistic features of the cationic copolymerization of lactones with cyclic ethers are studied for β-propiolactone (PL) with tetrahydrofuran (THF) and ?-caprolactone (CL) with THF. It is shown that, in the PL-THF system at [THF]₀ > [THF]_e, the copolymer is considerably enriched with the more basic THF whereas at [THF]₀ < [THF]_e anomalous enrichment of the copolymer with the less basic PL is observed. The mechanism of this phenomenon, which is applicable to many other cases and causes the formation of block copolymers from some heterocyclic monomers, is considered. At concentrations below equilibrium, THF is incorporated in the copolymer as pairs of units due to the effect of the penultimate unit on the thermodynamics of its addition.     

CHEMICAL STRUCTURE AND FUNCTIONAL PROPERTIES OF AMORPHOUS BORON CARBONITRIDE FILMS

Journal of Structural Chemistry - We report a comprehensive study of the effect of the chemical structure of boron carbonitride films on the variability of their functional characteristics. The...     

Modular structure of a sodium-rich analogue of eudialyte with the doubled c-parameter and the R3 symmetry

The structure of a new sodium-rich representative of the eudialyte group with the ideal formula (Na,Sr, K)₃₅Ca₁₂Fe₃Zr₆TiSi₅₁O₁₄₄(O,OH,H₂O)₉Cl₃ was established by the X-ray diffraction analysis (R = 0.054 based on 3503 |F|). The unit-cell parameters are a = 14.239(1), c = 60.733(7) Å, V = 10663.9 ų, sp. gr. R3. The mineral structure is characterized by in-layer order of cations resulting in doubling of the c-parameter and the formation of two modules, the composition and the structure of one of which corresponds to eudialyte (with an impurity of kentbrooksite), the prototype of the second module is alluaivite. Lowering of the symmetry is caused by ordering of Ca atoms and the Ca-replacing elements in the alluaivite module and by the displacements of the alkali cations from the m plane.     

Crystal structure of a new Mn, Na-ordered analogue of eudialyte with the symmetry R3

The crystal structure of a new representative of the eudialyte family was studied. This mineral is characterized by a low calcium content and by ordering the elements that isomorphically replace calcium, which lowers the symmetry from R3m to R3. The structure of the sample under study consists of the six-membered rings with two octahedra of substantially different volumes, one occupied mainly by manganese and the other, mainly by sodium and characterized by the average distances of 2.22 and 2.45 Å, respectively. The formation of such octahedra is the most characteristic structural feature of the third low-symmetry mineral of the eudialyte family.     

Large-scale simulations of a-Si:H: the origin of midgap states revisited

Large-scale classical and quantum simulations are used to generate a-Si:H structures. The bond-resolved density of the occupied electron states discloses the nature of microscopic defects responsible for levels in the gap. Highly strained bonds give rise to band tails and midgap states. The latter originate mainly from stretched bonds, in addition to dangling bonds, and can act as hole traps. This study provides strong evidence for photoinduced degradation (Staebler-Wronski effect) driven by strain, thus supporting recent work on a-Si, and sheds light on the role of hydrogen.     

Dependence of the drag of a conical axisymmetric cavitation body on the cone angle and the cavitation number

Numerical investigations of flow past axisymmetric conical captation bodies have shown that the drag coefficient of the cavitation body, calculated from the maximum cross-sectional area of the cavity (midsection), depends on the cavitation number and the cone angle.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 170–173, May–June, 1995.In conclusion, the author is grateful to G. Yu. Stepanov whose critical remarks were helpful in making this paper more conclusive and more illustrative.