Ring-Opening Polymerization of Lactones Initiated with Metal Hydroxide-Activated Macrocyclic Ligands: Determination of Mechanism and Structure of Polymers

Anhydrous alkali metal hydroxide (KOH, NaOH, and LiOH)-activated macrocyclic ligand complexing metal cations, i.e., coronands 12C4, 15C5, 18C6, DCH24C8, and cryptand C222, were selected for initiation of β-butyrolactone (β-BL) and ε-caprolactone (ε-CL) polymerization. It was found that β-BL polymerizes in the presence of KOH/18C6, KOH/C222, and NaOH/C222 systems. The real initiators in this case are two salts, potassium 3-hydroxybutyrate and potassium trans-crotonate, which are responsible for the formation of two fractions of the obtained polymer. ε-CL underwent polymerization with KOH or NaOH activated by all ligands used or without the ligand but with LiOH/12C4. Using KOH-activated strong ligands, i.e., 15C5, 18C6, or C222, two polymer fractions were generated containing linear and, unexpectedly, also cyclic macromolecules. The mechanism of the studied processes is discussed.     

SnS and SnS2 thin films deposited using a spin‐coating technique from intramolecularly coordinated organotin sulfides

Synthesis and applications of organotin(II) sulfide ({2,6‐(Me₂NCH₂)₂C₆H₃}Sn)₂(μ‐S) ( 1 ), organotin(II) thiophenolate {2,6‐(Me₂NCH₂)₂C₆H₃}Sn(SPh) ( 2 ) and organotin(IV) heptasulfide {2,6‐(Me₂NCH₂)₂C₆H₃}₂Sn₂S₇ ( 3 ) as potential single‐source precursors (SSPs) for the deposition of SnS or SnS₂ thin films using a spin‐coating method are reported. Compounds 1 , 2 and 3 differ either by tin oxidation state or by Sn:S ratio (Sn:S = 2:1 in 1 , 1:1 in 2 and 2:7 in 3 ). It is shown that compound 1 is not a suitable SSP for thin‐film fabrication using the spin‐coating process because of its incomplete decomposition at annealing temperature. However, compounds 2 and 3 seem to be promising SSPs for spin‐coating of amorphous semiconducting thin films of SnS and SnS₂, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Correction to: Thermodynamic model and Raman spectra of MgO–P2O5 glasses

Journal of Thermal Analysis and Calorimetry - Convection heat transfer in cavities has attracted much attention from researchers. Many kinds of nanofluids have exhibited non-Newtonian behavior and...     

Expedient Synthesis of Oxaboracyclic Compounds Based on Naphthalene and Biphenyl Backbone and Phase-Dependent Luminescence of their Chelate Complexes

The approach to a series of six- and seven-membered oxaboraheterocycles based on naphthalene or biphenyl backbones was developed. The key synthetic step involved Br/Li exchange in respective potassium (bromoaryl)trifluoroborates followed by quenching with selected electrophiles (CO₂, DMF, Me₂Si(H)Cl) and hydrolytic workup. Two ring-expanded benzoxaborole congeners were obtained by an additional reduction step with LiAlH₄ or NaBH₄. The obtained boracyclic compounds were characterized in detail by NMR spectroscopy and single-crystal X-ray diffraction. Specifically, biphenyl-based systems show dynamic behaviour interpreted in terms of inversion of non-planar seven-membered boraheterocycles. The acidity of the obtained compounds varies very strongly (pK_a ranges from 3.1–9.6) depending on their structure. Due to the enhanced boron Lewis acidity, selected compounds were used as a basis for luminescent complexes with 8-hydroxyquinoline. A strong phase-dependent variation of emission-band maximum (480–527 nm) and photoluminescence quantum yield (10–95 %) was observed, which was rationalized in terms of specific aggregation effects.     

Model Calculations and Experimental Studies as a Route Toward Simplification of the Kinetic Mechanism of the H2O2–NaSCN–NaOH–CuSO4 Homogeneous Oscillator

Oscillatory chemical reactions are usually characterized by complicated kinetic mechanisms in which the source of instability is combined with the parallel dissipative process. One of such systems is the H₂O₂–NaSCN–NaOH–CuSO₄ homogeneous oscillator, in which dynamic instabilities are associated with the irreversible oxidation of thiocyanate ions with hydrogen peroxide. Following our previous studies on this system, we now propose further intuitive and substantial simplification of its kinetic mechanism toward the scheme involving only five intermediates. Its compatibility with our previous, nine‐variable model is verified in terms of model calculations, compared with experimental potentiometric and spectrophotometric data. In particular, supercritical nature of a Hopf bifurcation as a route toward oscillations born out of a single steady state upon increasing catalyst (copper species) concentration was observed in the model and an analogous type of bifurcation is suggested by available experimental data. Our work is a step toward final reduction of the mechanism of the studied system to the “minimum oscillator,” the concept used earlier, e.g., for the Belousov–Zhabotinsky reaction, of however remarkably different kinetic mechanism.     

Crystallographic, vibrational and theoretical studies of 2,3-diaminopyridinium selenate

The new organic–inorganic salt, 2,3-diaminopyridinium selenate, has been synthesized and characterized by means of single-crystal X-ray crystallography, FT-IR and FT-Raman spectroscopy. A diprotonated organic ligand, H₂^1,3L²⁺, existing in the crystal structure was theoretically shown to be the most stable cationic species of 2,3-diaminopyridine. The weak non-covalent forces of N–H?O type between the hydrogen atoms of the amino and ammonio groups of 2,3-diaminopyridinium cation and oxygen atoms of tetrahedral selenate anions determine three-dimensional arrangement with complex network of intermolecular interactions of hydrogen bond type (donor–acceptor distances from 2.697(3) Å to 3.088(3) Å). Vibrational spectra have been discussed in comparison with X-ray results. Juxtaposition of spectra of the complex with the pure organic ligand and deuterated analogue of the title compound allowed to give reliable assignments of most observed vibrational bands. Presented data can be useful in elucidation of molecular mechanism of uptake of tetrahedral SeO₄²⁻ anion by the living organisms.     

Testing of the structure of macromolecular polymer films containing solid active pharmaceutical ingredient (API) particles

The aim of the present study was to investigate the structure of free films of Eudragit^® L 30D-55 containing different concentrations (0%, 1% or 5%) of diclofenac sodium by positron annihilation spectroscopy. The data revealed that the size of the free-volume holes and the lifetimes of ortho-positronium atoms decreased with increase of the API concentration. Films containing 5% of the API exhibited a different behavior during storage (17 °C, 65% relative humidity (RH)) in consequence of the uptake of water from the air.     

Void dynamics in lead-free Sn-Ag-Cu solder joints

As a result of thermal and mechanical loading of Sn-Ag-Cu solder joints pores, flaws and voids may nucleate and grow. Such void nucleation is studied here by means of a phase-field approach which accounts for the decomposition of the solder into phases described by its concentration c. In this investigation, the void growth results from boundary inward flux only, effects due to grain size and interstitials are not involved, cf. [1]. The free energy functional is approximated by a second order Taylor expansion and thus composed of a bulk free energy density and a Ginzburg-type gradient term. The bulk free energy density ϕ follows a classical Ginzburg-Landau double-well potential. The gradient-energy coefficient κ depends on ϕ and is calculated similar to [2]. Experimental data have been adapted for the modeling of the temporal evolution of the concentration of voids located on a square domain in 2D. The simulation is based on a B-spline finite element analysis. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Maximum cost scheduling of jobs with mixed variable processing times and k-partite precedence constraints

We present a polynomial algorithm for a family of single-machine scheduling problems with mixed variable job processing times, $k$ -partite job precedence constraints and the maximum cost criterion, provided that job processing times satisfy certain assumptions.