Radiochemical studies of free-radical vinyl polymerizations. VI. Polymerization of methyl methacrylate in the presence of organotin PVC stabilizers

¹⁴C-Azoisobutyronitrile was used to initiate polymerizations of methyl methacrylate in the presence of the organotin compounds: tetrabutyltin, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin di(ethyl mercaptide), dibutyltin di(dodecyl mercaptide), and dibutyltin dichloride. Only dibutyltin dichloride affected rates of polymerization significantly, and this was ascribed to an increase in the velocity constant k_p for the propogation reaction. No evidence was obtained for radical displacement reactions of the polymer radicals with bonds between tin and carbon, oxygen, sulfur, or chlorine. Transfer activity exhibited by the mercaptides was ascribed to traces of thiol impurity, possibly formed during storage. The relevance of these results to the mechanism of stabilization of poly(vinyl chloride) is briefly discussed.     

Connection between the electronic structure of tin in its compounds and the isomer shifts in the Mössbauer spectra

A formula is obtained which relates the isomer shifts in the Mössbauer spectra to the electronic structure of tin in its compounds. It is shown that these formulas describe the isomer shifts of various kinds of chemical compounds: tetravalent tin with -bonding (tin tetrahalides), tetravalent tin with no -bonding (compounds in which the tin is bound to alkyl, aryl, or metal carbonyl radicals), divalent tin, etc. The formulas are used to analyze the electronic structures of tin in compounds of these classes. It is shown that in tetravalent tin compounds with -bonding the isomer shift in the negative direction (with respect to -Sn) is due to the decreased number of 5s-valence electrons, and in the absence of -bonding, by an increase in the number of 5s-valence electrons.     

Studies of the thermal degradation of acetaminophen using a conventional HPLC approach and electrospray ionization-mass spectrometry

The thermal degradation of acetaminophen is studied via conventional accelerated aging studies by initially thermally stressing the compound at temperatures between 160 degrees C and 190 degrees C and measuring the rate of decomposition by reversed-phase high-performance liquid chromatography. Rates of decomposition of the compound in the dry state and the activation energy for the process are determined and compared with previously published kinetic and thermodynamic data for the degradation of acetaminophen in solution. In addition, the thermal fragmentation of acetaminophen under electrospray ionization (ESI) conditions using an interface with a heated capillary inlet is studied and the apparent activation energy for this process also is characterized. A comparison of the data shows that acetaminophen is significantly more stable in the dry state than in solution. However, the gas-phase fragmentation of acetaminophen under ESI conditions occurs more readily than either dry- or solution-state degradation. Although the resulting electrospray fragmentation mimics the breakdown product that is formed when the compound undergoes either acid or base catalyzed hydrolysis in aqueous solutions, the mechanism that produces the fragment ion appears to involve a two-step process. Initially, the parent ion forms of the analyte are produced in the spray region of the interface followed by wall-catalyzed decomposition and re-ionization in the heated inlet capillary of the spectrometer.     

Synthesis of Sybstituted Isoxazoles and Pyrazoles Based on 1-Aryl-3,4,4-trichloro-3-buten-1-ones

3-Aryl-5-methylenehydroxyiminoisoxazoles were synthesized by reaction of 1-aryl-3,4,4-trichloro-3-buten-1-ones with hydroxylamine. Reactions of ketones with hydrazine provided pyrazole structures; therewith two pyrazole molecules underwent coupling affording 3-arylpyrazole-5-carbaldehyde azines.     

Application of infrared spectroscopy to monitoring gas insulated high-voltage equipment: electrode material-dependent SF(6) decomposition

Sulfur hexafluoride is a chemically inert gas which is used in gas insulated substations (GIS) and other high-voltage equipment, leading to a significant enhancement of apparatus lifetime and reductions in installation size and maintenance requirements compared to conventional air insulated substations. However, component failures due to aging of the gas through electrical discharges may occur, and on-site monitoring for risk assessment is needed. Infrared spectroscopy was used for the analysis of gaseous by-products generated from electrical discharges in sulfur hexafluoride gas. An infrared monitoring system was developed using a micro-cell coupled to an FTIR spectrometer by silver halide fibers. Partial least-squares calibration was applied by using a limited number of optimally selected spectral variables. Emphasis was placed on the determination of main decomposition products, such as SOF(2), SOF(4), and SO(2)F(2). Besides the different electrical conditions, the material of the plane counter electrode of the discharge chamber was also varied between silver, aluminum, copper, tungsten, or tungsten/copper alloy. For the spark experiments the point electrode was the same material as chosen for the plane electrode, whereas for partial discharges a stainless steel needle was employed. Complementary investigations on the chemical composition within the solid counter electrode material by secondary neutral mass spectrometry (SNMS) were also carried out. Under sparking conditions, the electrode material plays an important role in the decomposition rates of the gas-phase, but no relevant material dependence could be observed under partial discharge conditions.     

Synthesis and photophysical properties of photochromic phenyl-substituted polyphenylenes with main-chain azobenzene fragments

New photochromic phenyl-substituted polyphenylenes containing azobenzene fragments in the backbone have been synthesized by the interaction of diacetylenes with bis(cyclopentadienones) via the Diels-Alder reaction. The polymers thus prepared exhibit the photochromic behavior and combine solubility in common organic solvents with high viscosity and thermal characteristics.     

Effect of total percent polyacrylamide in capillary gel electrophoresis for DNA sequencing of short fragments. A phenomenological model.

Polyacrylamide capillary gels were prepared with constant (5% C) cross-linker concentration and with total acrylamide concentration ranging from 2.5 to 6% T. At each acrylamide concentration, peak spacing was constant for DNA sequencing fragments ranging from 25 to 250 nucleotides in length. Peak spacing increased linearly with the total acrylamide concentration. The intercept of the retention time vs. fragment length plot was independent of % T. Ferguson plots were constructed for short DNA fragments; the polyacrylamide pore size falls in the 2.5 to 3.5 nm range for the gels studied. Theoretical plate count is independent of total acrylamide concentration; longitudinal diffusion, and not thermal gradients, limit the plate count. A phenomenological model is presented that predicts retention time, plate count, and resolution for sequencing fragments ranging in size from 25 to 250 bases and gels that range from 2.5 to 6% total acrylamide.     

RBS investigations of ion beam mixed hard coatings on tool steel

Silicon nitride hard coatings on tool steel produced by ion beam mixing following sputter or vapour deposition were investigated by RBS and Vickers microhardness measurements. Atomic mixing in the coating/steel interface region resulting in an improved adhesion and in a significant increase of the microhardness of the surface layers was found. Ion beam mixing with gas ions and high fluences leads to blistering of the implanted atoms in the silicon nitride layer.     

Alkaloids ofPetilium raddeana II. Structures of petisine and petisinine

The alkaloids imperialine, imperialone, peumisine, petiline, petilidine, and the new bases petisine (I) and petisinine (III) have been isolated from bulbs ofPetilium raddeana (Regl.) Vved. On the basis of spectral characteristics and passages to a known compound, the structure of 3-hydroxy-²²(N)-22,26-iminocholestane-6,23-dione has been established for (I) and petisine 3-glucopyranoside for (III).Institute of the Chemistry of Plant Substances of the Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 616–619, September–October, 1981.     

Magnetic behavior of copper diethyldithiocarbamate at low temperatures: A reinvestigation

The title compound, Cu(S₂CNEt₂)₂, behaves at low temperatures (1–20 K) as a normal spin-1/2 molecule, with 〈g〉 =2.06 and the Curie-Weiss θ = +0.25 K. This result contradicts an earlier investigation that led to the suggestion that the crystallographically-occurring dimers are coupled ferromagnetically.