Intermolecular association and supramolecular structures of PNVF–LiPFN and PVP–LiPFN complexes in the aqueous phase

Abstract

A new polymer–surfactant system, the poly(N-vinylformamide) (PNVF)–lithium perfluorononanoate (LiPFN) system, has been studied by a combination of the surface tension method and two-dimensional ¹H-¹⁹F heteronuclear Overhauser effect NMR spectroscopy (2D ¹H-¹⁹F HOESY). Using the surface tension method, we found that the critical aggregation concentration (cac) of LiPFN in the presence of PNVF is ca. 2 mM. In addition, the association behavior between LiPFN and PNVF is similar to that between poly(vinylpyrrolidone) (PVP) and LiPFN. The supramolecular structure of the PNVF–LiPFN complex in the aqueous phase is revealed by means of the 2D ¹H-¹⁹F HOESY experiment. On the basis of the intermolecular cross-relaxation between the PNVF protons and the LiPFN fluorines, we could conclude that the PNVF chain do penetrate into the LiPFN aggregate. The semi-quantitative analysis of the internuclear distance indicates that the PNVF chain is not located at the center core of the LiPFN aggregate, but the PNVF chain thread itself through the surface shell of the LiPFN aggregate instead. PNVF protons are nearest to the fluorines next to the carboxyl group, suggesting that the interaction between PNVF and LiPFN is mainly due to the dipole-ionic attraction. Moreover, we have reinvestigated the supramolecular structure of PVP–LiPFN complex and have found that the PVP chain also penetrates into the LiPFN aggregate. In contrast with the PNVF–LiPFN complex, the PVP chain in the PVP-LiPFN complex is rather close to the middle part of the LiPFN molecules which constitute the polymer-bound aggregate. This indicates that the formation of PVP–LiPFN complex involves more or less fluorophilic interactions.