Thermal degradation and flame retardance in copolymers of methyl methacrylate with diethyl(methacryloyloxymethyl)phosphonate

Methyl methacrylate (MMA) has been free radically copolymerized, both in bulk and in solution, with diethyl(methacryloyloxymethyl)phosphonate (DEMMP), to give polymers which are significantly flame retarded when compared with PMMA, as indicated by the results of limiting oxygen index (LOI) measurements, UL 94 tests, and the results of cone calorimetric experiments. The physical and mechanical properties of the copolymers are similar to those of PMMA, except that the bulk copolymers are slightly crosslinked, and are better than those of PMMA flame retarded to a similar extent by some phosphate and phosphonate additives. Examination of the some of the gaseous products of pyrolysis and combustion, and of chars produced on burning, show that flame retardation occurs in the copolymers by both a condensed-phase and a vapour-phase mechanism. The condensed-phase mechanism is shown to involve generation of phosphorus acid species followed by reaction of these with MMA units giving rise to methacrylic acid units. The methacrylic acid units subsequently form anhydride links, which probably impede depolymerization of the remaining MMA sequences, resulting in evolution of less MMA (the major fuel when MMA-based polymers burn). By undergoing decarboxylation, leading to interchain cyclisation and, eventually, to aromaticisation, the anhydride units are probably also the principal precursors to char.     

Applying Unconventional Spectroscopies to the Single-Molecule Magnets,Co(PPh3)2X2 (X=Cl,Br, I): Unveiling Magnetic Transitions and Spin-Phonon Coupling

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single-molecule magnets (SMMs). Spin-phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin-phonon coupling in molecules is challenging. We have found that far-IR magnetic spectra (FIRMS) of Co(PPh₃)₂X₂ ( Co-X ; X=Cl, Br, I) reveal rarely observed spin-phonon coupling as avoided crossings between magnetic and u-symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero-field split (ZFS) levels of the S=3/2 electronic ground state were probed by INS, high-frequency and -field EPR (HFEPR), FIRMS, and frequency-domain FT terahertz EPR (FD-FT THz-EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) and g values. Ligand-field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities in Co-X , showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spin-phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling.     

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Ohne Zusammenfassung     

On pseudo-plane deformations for the neo-Hookean material

For finite elastic deformations of the incompressible neo-Hookean material the problem of determining exact pseudo-plane deformations is considered. In particular three dimensional deformations are examined which are generated by replacing constants of an assumed known plane deformation with functions of a single space variable. Results are given for replacement of constants arising from translational and rotational invariance and stretchings. Finally two specific deformations are considered which provide new exact solutions for the neo-Hookean material.

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Zusammenfassung Exakte Lösungen für das Problem von pseudo-ebenen finiten Deformationen eines elastischen, inkompressiblen, neo-Hookeschen Materials werden ermittelt und diskutiert. Insbesondere werden dreidimensionale Deformationen studiert, welche durch Ersetzen der Konstanten einer als bekannt vorausgesetzten ebenen Deformation mit Funktionen einer einzigen Raumvariablen erzeugt werden. Resultate für den Ersatz der Konstanten aus Translations- und Rotationsinvarianz sowie aus Dehnungen sind aufgeführt. Schließlich werden zwei spezifische Deformationen betrachtet, welche zu neuen exakten Lösungen für das neo-Hookesche Material führen.

     

Studies on substituted phenols by differential pulse cathodic stripping voltammetry: 1. Pentachlorophenol

A study of chlorophenols using differential pulse cathodic stripping voltammetry (dpcsv) is reported. Of the wide range of chlorophenols investigated, only pentachlorophenol and 2,3,4,6-tetrachlorophenol yield stripping peaks.For pentachlorophenol in water, two peaks are obtained at stripping potentials of –1.2 V and –1.58 V versus SCE. In methanol, pentachlorophenol shows one peak with a stripping potential at –1.6 V versus SCE.In the case of 2,3,4,6-tetrachlorophenol in water, two peaks are observed at –1.06 V and –1.6 V versus SCE, while in methanol only one peak arises at a stripping potential of –1.6 V. A procedure was developed for the determination of pentachlorophenol in natural waters.     

The differential and total bulk acoustic scattering cross sections of some human and animal tissues

This paper describes methods that have been developed for the accurate measurement of total and differential bulk acoustic scattering cross sections. Analysis is made of the sources of uncertainty entailed in measurements of this kind and a complete derivation is developed for the angular variation of the interrogated scattering volume. Experimentally determined values of differential scattering cross sections are reported for specimens of skeletal muscle, blood, liver, and secondary tumors arising in liver, obtained in the frequency range 4-7 MHz for scattering angles in the practically attainable range 60 degrees-150 degrees and also at 180 degrees (backscatter). A basis for extrapolating these results to other scattering angles can be derived from a combination of theoretical and experimental considerations, as presented in a companion paper [J. Acoust. Soc. Am. 79, 2048-2054 (1986)]. Based on such extrapolation, values for total scattering cross sections are estimated for the above tissues, the values are compared with determinations by different techniques as reported by other authors, and corresponding estimates are derived for the contribution of scattering processes to total attenuation in the tissues.     

Prophet inequalities for averages of independent non-negative random variables

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