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Papers by Antonio Guarda
Journal of Fluorine Chemistry, Feb 1, 2004
Perfluoropolyethers (PFPEs) are a class of high performance materials used in a wide range of app... more Perfluoropolyethers (PFPEs) are a class of high performance materials used in a wide range of applications (refrigeration, lubrication, semiconductor industry, etc.). PFPEs containing peroxidic units are intermediate materials for the preparation of commercial end products. In this work we study the spectroscopic properties of ether and peroxides linkages in this class of compounds; nuclear magnetic resonance (NMR) spectra are discussed,
Macromolecules, 1999
The fluorine-initiated reaction of tetrafluoroethylene with oxygen, in a liquid phase at low temp... more The fluorine-initiated reaction of tetrafluoroethylene with oxygen, in a liquid phase at low temperature, leads to almost quantitative yields of polymeric perfluoroethers made by CF2CF2O and CF2O units and containing variable amounts of peroxy bonds. This chain reaction is studied in a series of semibatch experiments, and the results are interpreted on the basis of a rather simplified reaction mechanism involving a sequence of elementary steps of different free-radical species. A most unexpected experimental finding is the positive action exerted by the oxygen pressure on the initiation rate; this effect is attributed to a competitive reaction of fluorine atoms with molecular oxygen to form FO 2 reactive species which are able to produce a substantial number of chain-initiating biradicals. The kinetic relationships deduced from the overall reaction model are proved to fairly describe, in a quantitative way, the correlation between the operating variables and the various polymer structure indexes. The values of the typical kinetic parameters of the process are estimated; they appear to be consistent with an emerging general picture of the reactivity characteristics of the different perfluorinated oxygenated radical species in the condensed state.
The Journal of Physical Chemistry B, 2006
After a broad scouting based on quantum chemical calculations, optical absorption measurements in... more After a broad scouting based on quantum chemical calculations, optical absorption measurements in the vacuum ultraviolet (VUV) wavelength region between 140 and 190 nm were performed on a narrower series of commercial and experimental liquids. By elimination of sources of external contamination, mainly due to atmospheric gases, the analysis of the contributions to the absorption related to the backbone structure and to the chain end composition allowed the synthesis of a novel family of linear perfluoropolyethers (PFPEs) with optical absorbance at 157 nm between 0.3 and 0.6 cm(-1) in a broad range of compositions and molecular weights. The dependence of the optical threshold on the PFPE composition demonstrates that -OCF2- is the most transparent segmental unit in the VUV region.
Radiation Physics and Chemistry, 1996
Radiation Physics and Chemistry, 1995
ABSTRACT The investigation on the radiation chemistry of the perfluoropolyethers carried on throu... more ABSTRACT The investigation on the radiation chemistry of the perfluoropolyethers carried on through the analysis of the free radicals intermediates, of the structural changes in the oligomers chains and with the support of M.O. calculations has afforded information on the major features of the mechanism of radiolysis. The main radiolytic process is chain degradation by CC and CO bond rupture. Evidence of a minor participation of CF bond scissions have been obtained in the case of poly(perfluorotrimethylene oxide) PF3MO and poly(perfluoroethylene-perfluoromethylene oxide) PFEMO. The nature of the radicals intermediates and the structure of the novel units produced in the oligomer chains fit a radiolysis mechanism where both the ionic and excitation paths seem to be operative giving rise to complex sequence of radical reactions. The structure and possible reaction modes of the molecular cation and anion radicals are discussed on the basis of PM3 semi-empirical M.O. calculations.
Journal of Fluorine Chemistry, Feb 1, 2004
Perfluoropolyethers (PFPEs) are a class of high performance materials used in a wide range of app... more Perfluoropolyethers (PFPEs) are a class of high performance materials used in a wide range of applications (refrigeration, lubrication, semiconductor industry, etc.). PFPEs containing peroxidic units are intermediate materials for the preparation of commercial end products. In this work we study the spectroscopic properties of ether and peroxides linkages in this class of compounds; nuclear magnetic resonance (NMR) spectra are discussed,
Macromolecules, 1999
The fluorine-initiated reaction of tetrafluoroethylene with oxygen, in a liquid phase at low temp... more The fluorine-initiated reaction of tetrafluoroethylene with oxygen, in a liquid phase at low temperature, leads to almost quantitative yields of polymeric perfluoroethers made by CF2CF2O and CF2O units and containing variable amounts of peroxy bonds. This chain reaction is studied in a series of semibatch experiments, and the results are interpreted on the basis of a rather simplified reaction mechanism involving a sequence of elementary steps of different free-radical species. A most unexpected experimental finding is the positive action exerted by the oxygen pressure on the initiation rate; this effect is attributed to a competitive reaction of fluorine atoms with molecular oxygen to form FO 2 reactive species which are able to produce a substantial number of chain-initiating biradicals. The kinetic relationships deduced from the overall reaction model are proved to fairly describe, in a quantitative way, the correlation between the operating variables and the various polymer structure indexes. The values of the typical kinetic parameters of the process are estimated; they appear to be consistent with an emerging general picture of the reactivity characteristics of the different perfluorinated oxygenated radical species in the condensed state.
The Journal of Physical Chemistry B, 2006
After a broad scouting based on quantum chemical calculations, optical absorption measurements in... more After a broad scouting based on quantum chemical calculations, optical absorption measurements in the vacuum ultraviolet (VUV) wavelength region between 140 and 190 nm were performed on a narrower series of commercial and experimental liquids. By elimination of sources of external contamination, mainly due to atmospheric gases, the analysis of the contributions to the absorption related to the backbone structure and to the chain end composition allowed the synthesis of a novel family of linear perfluoropolyethers (PFPEs) with optical absorbance at 157 nm between 0.3 and 0.6 cm(-1) in a broad range of compositions and molecular weights. The dependence of the optical threshold on the PFPE composition demonstrates that -OCF2- is the most transparent segmental unit in the VUV region.
Radiation Physics and Chemistry, 1996
Radiation Physics and Chemistry, 1995
ABSTRACT The investigation on the radiation chemistry of the perfluoropolyethers carried on throu... more ABSTRACT The investigation on the radiation chemistry of the perfluoropolyethers carried on through the analysis of the free radicals intermediates, of the structural changes in the oligomers chains and with the support of M.O. calculations has afforded information on the major features of the mechanism of radiolysis. The main radiolytic process is chain degradation by CC and CO bond rupture. Evidence of a minor participation of CF bond scissions have been obtained in the case of poly(perfluorotrimethylene oxide) PF3MO and poly(perfluoroethylene-perfluoromethylene oxide) PFEMO. The nature of the radicals intermediates and the structure of the novel units produced in the oligomer chains fit a radiolysis mechanism where both the ionic and excitation paths seem to be operative giving rise to complex sequence of radical reactions. The structure and possible reaction modes of the molecular cation and anion radicals are discussed on the basis of PM3 semi-empirical M.O. calculations.