Molecular interactions and CO2-philicity in supercritical CO2. A high-pressure NMR and molecular modeling study of a perfluorinated polymer in scCO(2)

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Abstract

The carbon and fluorine chemical shifts of mixtures of carbon dioxide and Krytox, a carboxylic acid end-capped perfluorinated polyether used as stabilizer for the dispersion polymerization of methyl methacrylate, have been studied using high-pressure, high-resolution nuclear magnetic resonance. (13)C and (19)F spectra were measured in the density region between 0.54 and 0.73 g.cm(-3) at 334 K for different solutions of Krytox in scCO(2) (0.22, 1.13 and 1.72 w/w %). An in-house developed high-pressure apparatus with the capability to change in situ the sample composition was used for this purpose using a 10 mm polyether ketone NMR tube. The nature of CO(2)-Krytox interaction was assessed both by comparing the CO(2) delta(C) variation of neat CO(2) with that of mixtures with increasing surfactant composition and by the analysis of Krytox (19)F corrected chemical shifts in terms of medium magnetic susceptibility. Ab initio calculations, at the second-order Moller-Plesset level of theory to include the effects of electron correlation, were performed to access and compare the nature of the interactions between CO(2) and perfluorinated and nonfluorinated analogue model molecules. Both experimental (13)C and (19)F HP-NMR results and molecular modeling studies support a F...CO(2) site-specific Lewis acid-Lewis base interaction model. A positive entropic variation for the formation of CO(2)-fluorinated solute complex is advanced as an explanation for the higher solubility of perfluorinated molecules when compared to the nonfluorinated analogues.
Original languageUnknown
Pages (from-to)1318-1326
JournalJournal Of Physical Chemistry B
Volume111
Issue number6
DOIs
Publication statusPublished - 1 Jan 2007

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