Electrochemical reductive carbonization of poly(tetrafluoroethylene) with alkali metal (Li, Na, K) amalgams leads to a polymeric carbon with a partly carbynoid structure. Raman spectra measured in situ exhibited a strong line at around 2000 cm-1 which was interpreted as the C=C-C stretching mode of a linear carbon chain with alternating carbon-carbon triple and single bonds (polyyne). The intensity and position of this line evidence an unusually high triple bond carbon content in our materials, which leads to relatively large conjugation lengths in the polyyne chains. The triple bond line shifts to higher wavenumbers with increasing laser energy; this can be elucidated in terms of the conjugation length model. A quantum chemical calculation for transition energies and matrix elements of oligoynes with different chain lengths is presented. In addition, the frequency of the mode as a function of chain length is calculated. The conjugation lengths found correspond to 8-14 C atoms in the polyyne chain and increase with increasing atomic number of the alkali metal. The yield of polyyne and its stability against interchain cross-linking increase similarly. This supports our previous conclusions about the polyyne stability which were formulated on the basis of electronic conductivity and UV-vis spectra.

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SynopsisThe known method of surface treatment of poly(tetrafluoroethy1ene) (Teflon) by alkali metals was studied quantitatively. It was shown that the reaction proceeds by an electrochemical mechanism in solid phase. The alkali metal acts as anode and Teflon as a cathodic active material of a typical galvanic corrosion cell. A relation describing the rate of the penetration of this reaction into the depth of Teflon was derived.

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Defluorination of a film of highly oriented poly(tetrafluoroethylene) (PTFE) was carried out by the action of lithium and sodium amalgams. The reaction yields a composite product containing carbon with the equivalent amount of alkali metal fluoride. This material was studied by X-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy. The carbonized film is sensitive to surface oxidation upon contact to air. Part of the carbon in the product shows an unusual structure based on sp-bonded carbon chains. The amalgam-induced defluorination of PTFE influences markedly the surface morphology on the micron scale. Moreover, the molecular-level ordering of the precursor is reconstructed in the product of carbonization, presumably due to oxidative breakdown.

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