Condensation polymers from 1,2,5-thiadiazole-3,4-dicarboxylic acid

A series of polyamides was prepared by interfacial polymerization of diamines with 1,2,5-thiadiazole-3,4-dicarbonyl chloride. Polyamides from secondary cycloaliphatic diamines and aromatic diamines have high softening points, high glass transition temperatures, and good thermal stability. Secondary amines, in particular cycloaliphatic secondary amines, form very high molecular weight polyamides. The polyamide from trans-2,5-dimethylpiperazine and 1,2,5-thiadiazole-3,4-dicarbonyl chloride is soluble in chloroform and 1,1,2-trichloroethane and has been cast into films and spun into fibers from those solvents. Fibers of this polymer are strong and have very high work recovery from small strains. In addition, these fibers show good retention of strength and work recovery over a range of temperatures and humidities.     

The influence of cyclic alcohols on the temperature of maximum density of water

The effect of a homologous series of cyclic monohydric alcohols (C₄−C₈) on the temperature of maximum density of water has been examined. The structural contribution to the shift in the temperature of maximum density (TMD) is positive (increased structuredness) for alcohols up to C₆ but becomes negative at C₈. The behavior is compared with that of linear monohydric alcohols and Ω-diols.     

Flow-injection methods for the determination of uracil derivatives with voltammetric detection

Flow-injection methods are described for the determination of 18 uracil derivatives and related compounds, by means of differential-pulse amperometry (d.p.a.) or differential-pulse cathodic stripping voltammetry (d.p.c.s.v.). The carrier stream is a borax/KNO₃/HNO₃ (of NaOH) solution containing 0.001% (v/v) Triton X-100. This surfactant displaces the oxygen reduction peak to such negative potentials that deaeration is unnecessary for detection of compounds having peak potentials in the range 180–70 mV (vs. Ag/AgCI) at pH 7.6. At the hanging mercury drop electrode, the uracil derivative is deposited from the flowing sample at a fixed potential more positive than the relevant peak potential and stripped under stopped-flow or slow-flow conditions. In the amperometric mode, a constant potential also more positive than the relevant peak potential is applied to the dropping mercury electrode and the resulting peak is measured under flow conditions. Linear calibration graphs were found for most of the compounds at 10^?6–10^?7 M by d.p.a, and about one order of magnitude lower by d.p.c.s.v.. The limit of determination for 5-iodouracil was 5×10^?9 M (ca. 1.2 ng ml^?1). Separation is needed for applications to blood or urine. Simple deproteination followed by high-performance liquid chromatography with a reversed-phase column proved satisfactory. Separations of various uracil derivatives, and of 5-fluorouracil, uric acid and 5-fluorodeoxyuridine, are described; spectrophotometric and amperometric detectors were used sequentially to check performance.     

The determination of carbon and hydrogen in organic compounds containing metals and metalloids

The determination of carbon and hydrogen in organometallic compounds is described. Cobalto-cobaltic oxide is used as the catalytic tube filling in a rapid procedure. Compounds containing Na, K. Cu, Be, Mg, Ca. Zn, Cd, Hg, Al, B, Ga, Ti, Pb, Nb. P, As, Bi, Mo. U, Sc, Te, Mn, Fe, Co, Ni were examined; interferences were overcome where necessary and tungstic oxide proved a valuable auxiliary reagent.     

Determination of the rate constants for the NH2(X2B1) + NH2(X2B1) and NH2(X2B1) + H Recombination reactions with collision partners CH4, C2H6, CO2, CF4, and SF6 at low pressures and 296 K. Part 2

The recombination rate constants for the reactions NH2(X2B1) + NH2(X2B1) + M → N2H4 + M and NH2(X2B1) + H + M → NH3 + M, where M was CH4, C2H6, CO2, CF4, or SF6, were measured in the same experiment over presseure ranges of 1-20 and 7-20 Torr, respectively, at 296 ± 2 K. The NH2 radical was produced by the 193 nm laser photolysis of NH3. Both NH2 and NH3 were monitored simultaneously following the photolysis laser pulse. High-resolution time-resolved absorption spectroscopy was used to monitor the temporal dependence of both species: NH2 on the (1)2(21) ← (1)3(31) rotational transition of the (0,7,0)A2A1 ← (0,0,0)X2B1 electronic transition near 675 nm and NH3 in the IR on either of the inversion doublets of the qQ3(3) rotational transition of the ν1 fundamental near 2999 nm. The NH2 self-recombination clearly exhibited falloff behavior for the third-body collision partners used in this work. The pressure dependences of the NH2 self-recombination rate constants were fit using Troe’s parametrization scheme, k(inf), k(0), and F(cent), with k(inf) = 7.9 × 10(-11) cm3 molecule(-1) s(-1), the theoretical value calculated by Klippenstein et al. (J. Phys. Chem. A113, 113, 10241). The individual Troe parameters were CH4, k(0)(CH4) = 9.4 × 10(-29) and F(cent)(CH4) = 0.61; C2H6, k(0)(C2H6) = 1.5 × 10(-28) and F(cent)(C2H6) = 0.80; CO2, k(0)(CO2) = 8.6 × 10(-29) and F(cent)(CO2) = 0.66; CF4, k(0)(CF4) = 1.1 × 10(-28) and F(cent)(CF4) = 0.55; and SF6, k(0)(SF6) = 1.9 × 10(-28) and F(cent)(SF6) = 0.52, where the units of k0 are cm6 molecule(-2) s(-1). The NH2 + H + M reaction rate constant was assumed to be in the three-body pressure regime, and the association rate constants were CH4, (6.0 ± 1.8) × 10(-30); C2H6, (1.1 ± 0.41) × 10(-29); CO2, (6.5 ± 1.8) × 10(-30); CF4, (8.3 ± 1.7) × 10(-30); and SF6, (1.4 ± 0.30) × 10(-29), with units cm6 molecule(-1) s,(-1) and the systematic and experimental errors are given at the 2σ confidence level.     

A Note on “Modified Chain Displacement Function of Gaussian Networks” by A. H. Crossland

Crossland claims that the development of the conventional Gaussian theory of rubber elasticity does not take into account the requirement that the polymer chain end-to-end vector must be equal in direction to the network junction-to-junction vector. Reintroducing the directional probability, he develops a novel Gaussian strain-energy function. H correct, Crossland's work is a significant contribution, resulting in notable improvements in important models in rubber elasticity and polymer rheology. Unfortunately, there is an error in Crossland's analysis. Correction of the error reduces Crossland's results to those of the conventional Gaussian theory and shows that the conventional theory does correctly account for the directional probability. The “improved” strain-energy function, therefore, has no theoretical basis and, at best, must be considered purely empirical.     

Hydrocarbon Soluble Alkali-Metal-Aluminium Hydride Surrog[ATES]

A series of group 1 hydrocarbon-soluble donor free aluminates [AM(^tBuDHP)(TMP)Al(ⁱBu)₂] (AM=Li, Na, K, Rb) have been synthesised by combining an alkali metal dihydropyridyl unit [(2-^tBuC₅H₅N)AM)] containing a surrogate hydride (sp³ C−H) with [(ⁱBu)₂Al(TMP)]. These aluminates have been characterised by X-ray crystallography and NMR spectroscopy. While the lithium aluminate forms a monomer, the heavier alkali metal aluminates exist as polymeric chains propagated by non-covalent interactions between the alkali metal cations and the alkyldihydropyridyl units. Solvates [(THF)Li(^tBuDHP)(TMP)Al(ⁱBu)₂] and [(TMEDA)Na(^tBuDHP)(TMP)Al(ⁱBu)₂] have also been crystallographically characterised. Theoretical calculations show how the dispersion forces tend to increase on moving from Li to Rb, as opposed to the electrostatic forces of stabilization, which are orders of magnitude more significant. Having unique structural features, these bimetallic compounds can be considered as starting points for exploring unique reactivity trends as alkali-metal-aluminium hydride surrog[ATES].     

Micro‐photoluminescence spectroscopy on heavily‐doped layers of silicon solar cells

We report and explain the photoluminescence spectra emitted from silicon solar cells with heavily‐doped layers at the surface. A micro‐photoluminescence spectroscopy system is employed to investigate the total spectrum emitted from both the heavily‐doped layer and the silicon substrate with micron‐scale spatial resolution. The two regions of the device give rise to separate photoluminescence peaks, due to band‐gap narrowing effects in the highly‐doped layer. Two key parameters, the absorption depth of the excitation wavelength, and the sample temperature, are shown to be critical to reveal the separate signatures from the two regions. Finally, this technique is applied to locally diffused and laser‐doped regions on silicon solar cell pre‐cursors, demonstrating the potential value of this micron‐scale technique in studying and optimizing locally doped regions. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)