A theoretical investigation of molecular core binding and relaxation energies in a series of oxygen-containing organic molecules of interest in the study of surface oxidation of polymers

Nonempirical LCAO MO SCF computations (in the ΔSCF formalism) have been carried out of binding energies and relaxation energies for an extensive series of oxygen-containing organic systems encompassing most of the common functionalities. The molecules for which experimental data are available for comparison demonstrate the adequacy of the treatment for describing the relative binding energies for both the C_ls and O_ls core levels. A sound basis is therefore provided for the discussion of relative core binding energies (C_ls and O_ls) for functionalities for which experimental data are not available, that is, hydroperoxides, peroxides, peroxyacids, and peroxyesters, a knowledge of which is essential for investigations of the surface oxidation of polymers by means of ESCA. C_ls shifts are discussed in terms of primary and secondary substituent effects of oxygen, which greatly simplify the analysis of complex unresolved spectra, whereas for the O_ls levels a similar but less straightforward situation exists. The relaxation energies associated with both C_ls and O_ls core ionization follow a dependence on the binding energy for a given structural type.     

The structure of plasma-polymerized toluene: A solid-state 13C-NMR study of isotopically labeled polymers

A detailed magic angle spinning ¹³C-NMR investigation of the intractable polymer prepared by plasma polymerization of toluene and isotopically labeled toluene led to a proposed model for the structure of the polymer and suggested some of the likely processes that occur in the gas phase leading to film formation. From the ¹³C spectra four resolved resonances permitted the determination of the contribution of nonprotonated and protonated unsaturated as well as methyl and other aliphatic carbons to the polymer structure. Specific ¹³C isotopic labeling of the methyl and phenyl C-1 toluene carbons in the injected liquid vapor allowed the destination of these carbons in the deposited polymer to be traced. The dominant structure is derived primarily from two precursors: benzyl radical and toluene itself. The ¹³C data further requires a net saturation of ca. 30% of the toluene double bonds and a net displacement of hydrogen by carbon on ca. 20% of the toluene ring carbons.     

Esca applied to polymers. XXIII. RF glow discharge modification of polymers in pure oxygen and helium–oxygen mixtures

The oxidation of polyethylene, polypropylene, and polystyrene by exposure to plasmas excited in pure oxygen and helium–oxygen mixtures at low power levels has been studied. A detailed curve resolution procedure is outlined, and the rate of oxidation is shown to be a strong function of the polymer structure for pure oxygen plasmas, as is the composition of the oxidized layer; this is not the case, however, for oxidation effected by helium–oxygen mixtures. It seems likely, from a consideration of the available data, that the oxidation is confined to the outermost monolayer and is initiated by a crosslinking mechanism that involves oxygen-containing functionalities.     

ESCA applied to polymers. XXI. Investigation of sample-charging phenomena

Sample-charging phenomena arising in the ESCA experiment have been investigated for a series of polymers. For samples studied as films or powders mounted insulated from the spectrometer probe and for gold under similar conditions it is shown that over a wide range of operating conditions, equilibrium charging shifts are characteristic of the sample and show a strong dependence on the theoretically calculated total photoionization cross sections. The surface sensitivity of the phenomenon has been demonstrated by monitoring changes in charging shifts as a function of hydrocarbon contamination. For polymer films mounted directly in contact with the spectrometer, the charging shifts exhibit time-dependent behavior. The utility of studying sample-charging shifts as an interesting phenomenon in its own right is demonstrated by reference to changes which occur consequent upon surface modification of an ethylene–tetrafluoroethylene copolymer system in RF plasmas excited in inert gases.     

The identification of peroxy-features at polymer surfaces by ESCA

A preliminary investigation of the identification of peroxy-features at polymer surfaces by ESCA is described. Oxidation of a hydrocarbon polymer in the effluent of a singlet molecular oxygen generator, based on a microwave discharge in oxygen, produces surfaces rich in peroxy-features. By comparison with experimental and theoretical studies of model systems these features can be identified in ESCA spectra by their characteristic O_1s binding energies. The oxygen atoms in the peroxy-linkage have essentially the same binding energy, which is within a narrow range of 534.0 eV for simple peroxides and hydroperoxides and a narrow range of 535.2 eV for peroxy-features in more highly oxygenated environments; for example, peracids and peresters. Peroxy-linkages decompose rather rapidly under the typical x-ray flux used in the ESCA experiment.     

Incorporation of Metals into Fluoropolymer Films Synthesized by Plasma Techniques

A method is described to incorporate metals into fluorocarbon polymer films produced in a plasma environment by a simultaneous etching and polymerization process. The emphasis of this work is on a molybdenum-perfluoropropane system, and films produced in this manner were found to contain as much as 20% molybdenum by weight. Some aspects of their structure are discussed.     

An investigation of the vacuum UV spectra of inductivity coupled RF plasmas excited in inert gases as a function of some of the operating parameters

The vacuum ultraviolet (UV) emission from inductively coupled radio-frequency (RF) plasmas excited in a series of inert gases has been studied as a function of the pressure and applied power of the system. The effects of discharge tube size and pulsing of the applied RF power are also considered and a comparison is made between RF and microwave excitation.     

Some aspects of shake-up phenomena in some simple polymer systems

Satellite peaks accompanying core ionizations are observed in polymers containing aromatic pendant groups. These satellites are absent in analogous saturated systems. CNDO/2 SCF MO calculations have been performed on model systems and the satellite peaks are interpreted as arising from shake-up processes involving π* ← π transitions in the aromatic system. The calculations correctly predict trends in satellite peak intensities and separations.     

Einige Bemerkungen zur Deutung von ESCA-Spektren F-haltiger Polymerer und deren Beziehung zum Kristallisationsgrad, zur Oberfl?chenspannung und zum Gehalt an adsorbiertem Gas

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