Incorporation of a flame retardancy enhancing phosphorus-containing diol into poly(butylene terephthalate) via solid state polycondensation: A comparative study

The phosphorus-containing aliphatic-aromatic diol 2-[4-(2-hydroxy-ethoxy)-3-(10-oxo-10-H9-oxa-10-λ5-phospha-phenanthrene-10-yl)-phenoxy]-ethanol, a potential flame retardant, was incorporated into poly(butylene terephthalate) (PBT) by solid state polycondensation. Thus, polymers with various ratios of PBT/DOPO-diol and number-average molar masses up to 57,000 g mol⁻¹ could be prepared. Their molar masses were higher than those of copolyesters with comparable composition obtained by direct melt polycondensation. Structures and properties of copolyesters produced by both methods were not significantly different after melt processing. Their thermal properties and combustion behaviour were investigated by means of DSC, TGA, and pyrolysis combustion flow calorimetry. Combustion studies revealed high char yields, very low heat release capacities and high limiting oxygen index (LOI) at rather low P-contents, indicative of better flame-retardancy properties.     

Effect of Lithium Tetrafluoroborate on the Solubility of Carbon Dioxide in the Ionic Liquid 1-Butyl-3-Methylimidazolium Tetrafluoroborate

In this work, the phase behavior of the ternary system of carbon dioxide +1-butyl-3-methylimidazolium tetrafluoroborate?+?lithium tetrafluoroborate has been investigated. Mixtures of known concentrations of the salt, ionic liquid and carbon dioxide were prepared and their bubble point pressures were measured at different temperatures. Results are reported for this ternary system, at carbon dioxide concentrations of 20.2, 27.6 and 35.2?mol-% and salt concentrations of 0.0, 6.0, 11.5, 16.3 and 21.1?mol-% (on a carbon-dioxide free basis) and within temperature and pressure ranges of 293.15?C358.15?K and 1.2?C11.3?MPa, respectively. It was observed that the addition of the salt increased the bubble point pressure and its effect was concentration-dependent, i.e. at higher concentrations of the salt, higher pressures are required. This behavior is greater at higher temperatures.     

Phase equilibria of mixed carbon dioxide and tetrahydrofuran hydrates in sodium chloride aqueous solutions

In this work, the competing effects of sodium chloride (NaCl) and tetrahydrofuran (THF) on carbon dioxide hydrate formation are investigated through phase equilibrium measurements. The phase behaviour in the hydrate forming region for the binary system carbon dioxide–water, the ternary systems carbon dioxide–tetrahydrofuran–water and ternary carbon dioxide–sodium chloride–water and, in addition, the quaternary system carbon dioxide–tetrahydrofuran–water–sodium chloride are determined experimentally, using a Cailletet apparatus. All measurements are made in a temperature and pressure region of 275–290 K and 0.5–7.0 MPa, respectively. In these ranges, three different hydrate equilibrium curves are measured namely: H-L_W-V, H-L_W-L_V-V and H-L_W-L_V. The formation of an organic-rich liquid phase in the systems due to a liquid–liquid two-phase split between water and tetrahydrofuran when pressurized with carbon dioxide causes the occurrence of an upper quadruple point (Q₂) to evolve into a four-phase H-L_W-L_V-V equilibrium line. The presence of sodium chloride in the quaternary system enhances the split between the two liquids due to the salting-out effect. It was found that the hydrate promoting effect of tetrahydrofuran is able to suppress the inhibiting effect of sodium chloride especially at lower concentration of sodium chloride.     

Generalization of a theorem of Kusmin

A Gauss-Kusmin theorem for the natural extension of the regular continued fraction expansion is given. A generalization of a theorem by D. E. Knuth is obtained by similar techniques.With 3 FiguresResearch of the first author supported by the Netherlands Organization of Scientific Research (NWO).     

Isomorphism of anhydrous tetrahedral halides and silicon chalcogenides: energy landscape of crystalline BeF2, BeCl2, SiO2, and SiS2

We employ periodic density functional theory calculations to compare the structural chemistry of silicon chalcogenides (silica, silicon sulfide) and anhydrous tetrahedral halides (beryllium fluoride, beryllium chloride). Despite the different formal oxidation states of the elements involved, the divalent halides are known experimentally to form crystal structures similar to known SiX2 frameworks; the rich polymorphic chemistry of SiO2 is however not matched by divalent halides, for which a very limited number of polymorphs are currently known. The calculated energy landscapes yield a quantitative match between the relative polymorphic stability in the SiO2/BeF2 pair, and a semiquantitative match for the SiS2/BeCl2 pair. The experimentally observed polymorphs are found to lie lowest in energy for each composition studied. For the two BeX2 compounds studied, polymorphs not yet synthesized are predicted to lie very low in energy, either slightly above or even in between the energy of the experimentally observed polymorphs. The experimental lack of polymorphism for tetrahedral halide materials thus does not appear to stem from a lack of low-energy polymorphs but more likely is the result of a lack of experimental exploration. Our calculations further indicate that the rich polymorphic chemistry of SiO2 can be potentially matched, if not extended, by BeF2, provided that milder synthetic conditions similar to those employed in zeolite synthesis are developed for BeF2. Finally, our work demonstrates that both classes of materials show the same behavior upon replacement of the 2p anion with the heavier 3p anion from the same group; the thermodynamic preference shifts from structures with large rings to structures with larger fractions of small two and three membered rings.     

Approaching Theoretical Performances of Electrocatalytic Hydrogen Peroxide Generation by Cobalt-Nitrogen Moieties

Electrocatalytic oxygen reduction reaction (ORR) has been intensively studied for environmentally benign applications. However, insufficient understanding of ORR 2 e⁻-pathway mechanism at the atomic level inhibits rational design of catalysts with both high activity and selectivity, causing concerns including catalyst degradation due to Fenton reaction or poor efficiency of H₂O₂ electrosynthesis. Herein we show that the generally accepted ORR electrocatalyst design based on a Sabatier volcano plot argument optimises activity but is unable to account for the 2 e⁻-pathway selectivity. Through electrochemical and operando spectroscopic studies on a series of CoN_x/carbon nanotube hybrids, a construction-driven approach based on an extended “dynamic active site saturation” model that aims to create the maximum number of 2 e⁻ ORR sites by directing the secondary ORR electron transfer towards the 2 e⁻ intermediate is proven to be attainable by manipulating O₂ hydrogenation kinetics.