X-ray photoelectron spectroscopy of an ethylene–tetrafluoroethylene copolymer

The electronic structure of a clean copolymer of ethylene and tetrafluoroethylene is investigated by measuring the ESCA spectra of the core and valence levels. The chemical composition and alternating (>95%) structure of the copolymer, characterized separately by classical methods, is verified by analyzing the C 1s core-level spectrum. The comparison of the experimental valence band with an original EHCO band-structure calculation, and with similar data for a model of polymer with block structure, shows that the combined methods allow us to distinguish between the two compounds through their valence-band spectra.     

AN ESCA STUDY OF THE ELECTRONIC STRUCTURE OF TETRATHIONAPHTHALENE AND TETRATHIOTETRACENE: TWO PLANAR AROMATIC BIS-DISULFIDES WITH SEMICONDUCTING PROPERTIES

Abstract

High resolution X-ray photoelectron spectra have been obtained for two planar aromatic bis-disulfides : tetrathionaphthalene (Fig. 1, N° 1) and tetrathiotetracene (Fig. 1, N° 2).     

The NMR reciprocity theorem for arbitrary probe geometry

It is shown that the NMR reciprocity theorem is a variant of a problem considered by Lorentz in 1895. This formulation is quite general and applies to electric-dipole-based as well as coil-based or resonator-based magnetic resonance probes. The reasoning is related to, but different from, the proof of the reciprocity theorem for radiofrequency networks and for transmit/receive antenna systems in telecommunications. The signal-to-noise ratio of the NMR experiment is also discussed in very general terms.     

Chemical structures assigned for the low molecular weight fractions from degradation of poly(styrene sulfides)

A non-destructive analysis is performed of thermally unstable sulfur-styrene reaction products, combining preparative size exclusion chromatography (P-SEC), ultraviolet-visible (UV-vis) and nuclear magnetic resonance (NMR). The crystallizing compounds are identified as be 2,4-diphenylthiophanes with short sulfur bridge (x ∼ 2) contrary to earlier suggestions which were based on destructive analysis. A new cyclic structure (styrene polysulfide x = 1 up to 8) was assigned to the amorphous species containing a single styrene repeating unit. Comparison with the amorphous fractions suggests that the rigid ring of styrene repeating units in adjacent sequences is the characteristic feature for the crystallisability. The melting and crystallization behaviour of this crystalline component was observed, by optical microscopy (OM) and differential scanning calorimetry (DSC), to be step-wise as well as broad, due to the variation in the length of the sulfur bridge.     

Electronic structure of fluoropolymers : Theory and esca measurements

Theoretical and experimental results for the band structure of fluoropolymers are presented. Original theoretical results are obtained from the extende Hückel method of the following polymers : (I) polyethylene, (II) polyvinyl fluoride, (III) polydifluoro (1,2) ethylene-cis, (IV) polydifluoro (1,2) ethylene-trans, (V) polyvinylidene fluoride, (VI) polytrifluoroethylene and (VII) polytetrafluoroethylene. Band structures schemes and density of state histograms are calculated. Results are compared with valence band structures as revealed by E.S.C.A. spectroscopy, using a flood gun to neutralize char effects on these compounds. In this work, accent is put on the substituent effect of fluorine. Correlation between theoretical and observed density of