Homolytic reactions of polyfluoroaromatic compounds V. The reaction of pentafluorophenyl radicals with fluorobenzene

The arylation of fluorobenzene with pentafluorophenyl radicals obtained by the reaction of the corresponding aniline with pentyl nitrite is described. The reaction involves attact at the 2t?-,3t?-and 4t?-positions. The composition of the mixture and the nature of its components were determined by ¹⁹F NMR spectroscopy and were confirmed by gas-liquid chromatography.     

Synthetic thermally reversible gel systems. V

Differential thermal analysis has been used to study the fusion of aqueous thermally reversible gels of gelatin and polyacrylylglycinamide (PAG). In the case of gelatin gels, endotherms close to the melting point are readily observed and these are sometimes preceeded by a small exothermic heat of gel reorganization. Calculations are presented to show that breaking of the gelatin gel network requires only a small fraction of the observed endothermic heat of fusion and that most of the heat is required for melting larger crystallites within gelatin aggregates and for perhaps a helix → coil transition. Failure to observe endotherms by DTA over the known temperature range of fusion of PAG gels is consistent with prior measurements and conclusions. The noncrystallinity of PAG gels and soluble aggregates together with a heat of crosslinking of only ?5 to ?10 kcal/mole of crosslinks places the heat of fusion of PAG gels outside the lower limits of DTA sensitivity.     

Elastic properties of crosslinked poly(vinyl alcohol) gels: Network topology

Current network theory exhibits inconsistencies which show up particularly clearly in deformation of networks prepared by crosslinking a polymer in solution. A check of theory can be obtained if one knows precisely the number of crosslinks in the network and if a range of deformations is applied to the network. In an effort to explore this problem we have examined the relation of shear modulus to crosslink density, primary molecular weight, and polymer concentration for a series of poly(vinyl alcohol) gels at low to intermediate concentrations. Aqueous poly(vinyl alcohol) solutions were crosslinked to form infinite networks using terephthalaldehyde. We find a large discrepancy with these poly(vinyl alcohol) gels between measured shear modulus and that calculated from classical elasticity theory assuming quantitative reaction of crosslinking. The ratio of measured to calculated modulus is independent of crosslink density for a given primary molecular weight and concentration. It shows linear dependence on polymer concentration prior to crosslinking and extrapolates to a critical concentration which is consistent with the effective sizes of the polymer molecules.     

Potentiometric titration of hydrogen peroxide with an electropolished stainless steel electrode

The preparation and use of a stainless steel indicator electrode in the accurate potentiometric titration of aqueous hydrogen peroxide are described. The results agree excellently with those obtained by a standard colorimetric weight-titration procedure. The nature of the titration curves, potential changes and the factors affecting them are discussed. Rapid potentiometric titrations directly to the equivalence-point potential are possible, owing to the nature of the titration curve.     

Influence of extended π-conjugation units on carrier mobilities in conducting polymers

Carrier mobilities in thin films of copolymers with repeat units consisting of oligothiophenes bridged by Si atoms are measured over a range of doping levels, where the numbers of thienylenes in the repeat unit are 7, 8, 10, 12, and 14. The mobilities for these polymer films increased with the increase in doping level and the mobility enhancement followed an increasing order of the π-conjugation length. The magnitude of the mobility increase for the Si polymer comprising 14 thiophene units reached ca. 10⁴, implying that this π-conjugation length is almost sufficient to reproduce transport properties of polythiophenes.     

Gas-chromatographische Bestimmung von Mono-, Di- und Tri?thylenglykol in Wasser

Ohne Zusammenfassung

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Gas-chromatographie determination of ethylene glycol, diethylene glycol and triethylene glycol in water

     

A new solid-phase polymerization—metal phthalocyanine sheet polymers

The thermal reactions of pure metal(11) 4,4′,4″,4′″-phthalocyanine-tetracarboxylic acids of copper, cobalt, and nickel at 350–400°C in vacuum have been studied using Fourier transform infrared spectrometry, gas chromatography, and mass spectrometry. Based on these observations, novel in situ reactions for the synthesis of heat-resistant phthalocyanine “sheet” polymers are described. The poly(metal phthalocyanine) polymers of copper, cobalt, and nickel so synthesized have been characterized by elemental analysis, infrared spectroscopy, and dynamic thermogravimetric analysis. The most noteworthy property of these polymers is their extreme resistance to heat in an anaerobic atmosphere and their high char yields (89–93%) at 800°C in a nitrogen atmosphere.     

Double-layer effects on simple electrode reactions III. The reduction of Eu3+ and Cr3+ in the presence of thiocyanate anions. Evidence for ligand bridging

The rates of reduction of Eu³⁺ and Cr³⁺ have been measured in mixed perchlorate + thiocyanate electrolytes at constant ionic strength, using low concentrations of thiocyanate to minimize its association with the cationic reactants. The effect of adsorbed thiocyanate anions on the reduction kinetics of Cr³⁺ resembled those produced by iodide and bromide on both Cr³⁺ and Eu³⁺. However, thiocyanate exhibited an unusual catalytic effect on the reduction of Eu³⁺ which was identified as arising from a reaction pathway involving thiocyanate-bridging between the mercury surface and the Eu³⁺. The diagnostic criteria used to support the proposed mechanism included analysis of the rate—potential behavior and of the effects of competitively adsorbed iodide ions upon the reduction rates.     

Preparation and chain extension of C100dicarboxylic acid

The selective degradation of polyethylene crystals with fuming nitric acid has been used to prepare a C₁₀₀ chain with terminal functional groups. After treating this product with concentrated sulphuric acid, it is shown by average molecular weight, titration and infra-red spectroscopy measurements that each molecule contains two carboxylic acid groups. This C₁₀₀ dicarboxylic acid is chain extended with several low molecular weight difunctional coupling agents. Block copolymers of this acid and poly(propylene glycol) have been prepared.     

Extraction properties of octaethyltetraamidopyrophosphate (OETAPP)

The extraction of uranium was studied in the system of 0.1 M OETAPP in CHCl₃/HCl or HNO₃. The distribution coefficients of HCl and HNO₃ were calculated as a function of OETAPP concentration. The amount of OETAPP in the aqueous phase containing HCl and HNO₃ was found from the measurements of surface tension of this phase. The distribution of HCl and HNO₃ between an organic and aqueous phase was studied as a function of the concentration in the aqueous phase of the acid in question. The solvation energy of the extracted complexes was calculated on the basis of the measured potential differences. The cohesion and adhesion energies of the studied systems are given as well.