Charge compensation dynamics in a soluble copolymer of poly(aniline) and poly(phenylene sulfide)

Poly(phenylene sulfide phenyleneamine), PPSA, is a copolymer of poly(aniline) and poly(phenylene sulfide), soluble in conventional organic solvents as tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, and cyclohexanone. In this research, its electrochemical behavior has been studied in acetonitrile in the presence of different electrolytes, where the loss of electroactivity was observed after few cycles. In this paper, the charge compensation dynamics of PPSA is analyzed through electrochemical quartz crystal microbalance experiments and electroacoustic impedance measurements. Raman spectroscopy data have shown that once the oxidation of the sulfur atom occurs, a loss of electroactivity is observed, being not possible to recover the pristine state of the polymer. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) data obtained for the fully oxidized polymer are consistent with the formation of a networked polymer due to the electrophilic attack of the positive sulfur atom on the activated aromatic rings. Electrochemical quartz crystal microbalance results clearly show that the degree of irreversibility fully depends on the chemical nature of the anions with a negligible participation of the cations of the electrolytic solution. This work is in memoriam of Prof. Dr. Francisco C. Nart, dearest friend and colleague, whose scientific skills and enthusiasm will always be remembered.     

Thermal degradation of copolymers of styrene and methyl-vinyl-silane by pyrolysis gas chromatography

Pyrolysis gas chromatographic investigations have been carried out on copolymers of styrene with trimethyl-vinyl-silane and of styrene with dimethyl-phenyl-vinyl-silane, in order to study the mechansims of thermal degradation and the copolymer structures. We have identified the pyrolysis products and measured their relative amounts. The experiments show that the controlling factor in the mechanism of the degradation is the nature of the side-group attached to the carbon atom at which chain scission occurs. If this side-group is phenyl, the main degradation process is depropagation; if it is if it is trimethyl-silyl or dimethyl-phenyl-silyl, intramolecular hydrogen abstraction followed by β scission becomes more important than depropagation. From the point of view of degradation mechanism, the nature of the side-group attached to the carbon atom from which the hydrogen is abstracted is of minor importance.We estimated the average copolymer block length from the amounts of products containing both comonomers as well as from the amounts of trimer composed of the same monomer.     

Vapor-particle partitioning of hydrocarbons in Western Mediterranean urban and marine atmospheres

An analytical procedure is described for a comprehensive determination of the composition of hydrocarbons in the atmosphere, based on: (a) aerosol filtration and subsequent adsorption of the vapor phase onto active charcoal and polyurethane foam; (b) GPC and HPLC fractionation of the extracts, and (c) analysis of the fractions by GC-MS under EI and NICI modes. Special emphasis is placed onn-alkanes, PAHs and their oxygenated derivatives.The characterization of samples collected in a coastal urban area (Barcelona city), and far away over the Western Mediterranean, at sea level and at 1100 m of altitude, revealed significant changes in the aerosol composition, mainly attributed to initial vapor-particle partitioning processes, influenced by ambient temperature variations, and to others taking place during long-range atmospheric transport, related with the different compound photoreactivities and with an unexplained source-decoupling phenomenon.     

Molybdenum(VI) and molybdenum(V) mononuclear and dinuclear complexes with 1,3-diphenyl-1,3-propanedione

Summary The synthesis and the dinuclear or mononuclear nature of several molybdenum(VI) and molybdenum(V) oxocomplexes derived from 1,3-diphenyl-1,3-propanedione (HLL) are described. These complexes were identified by i.r. and electronic spectra, magnetic susceptibility and analytical data, and are assigned the following formulae: [MoO₂(LL)₂], [Mo₂O₅(LL)₂], [Mo₂O₄(LL)₂], [MoOCl(LL)₂], [MoCl₂(LL)] and [MoO(OH)(LL)₂)]. The low magnetic moments of the dinuclear complexes are due, in part, to intramolecular interactions. The i.r. data show that the dionate is bound by two oxygen atoms forming a chelate six-membered ring.     

Fission barriers for Na N 2+ cluster dissociation

The competition experimentally observed between asymmetric fission and neutral monomer evaporation as dissociation channels of excited doubly charged sodium clusters has been investigated by means of an axially symmetric, fully selfconsistent Kohn-Sham method. Ellipsoidal equilibrium configurations for parent and daughter clusters have been considered using a deformed jellium model.This paper was originally submitted in connection with the 2nd. Int. Conference on Atomic and Nuclear Clusters held in Santorini from 28. June–2. July 1993 and is published here as a regular article after an independent refereeing procedure according to the standards of Z. Phys. D     

Role of montmorillonite in flame retardancy of ethylene-vinyl acetate copolymer

The effects of non-treated (MMT), organophilic (OMM), and olefin/silicone polymer intercalated (IMM) montmorillonites on the thermal stability of ethylene-vinyl acetate copolymer (EVA) and on the flammability of magnesium hydroxide filled EVA were studied. The influence of various treatments on the delamination of montmorillonites in EVA was detected by rheological measurements and by Raman microscopy. The latter was a unique method for rapid detection of the dispersion also in highly filled EVA. Enhancement of thermo-oxidative stability of EVA and flame-retarded EVA could be observed by thermal analysis in the presence of variously treated montmorillonites. The flame-retardant efficiency of magnesium hydroxide was improved by simultaneous application of MMT and IMM. The increased performance of magnesium hydroxide was explained by the rheological effect of the IMM, catalytic effect of MMT and chemical interactions of montmorillonites with the metal hydroxide.