Intramolecular and intermolecular OH. . .O and OH. . .F interactions in perfluoropolyethers with polar end groups: IR spectroscopy and first-principles calculations

Perfluoropolyether (PFPE) fluids constitute a class of polymers that fulfil a wide range of requirements for hi-tech applications, due to their pefluorinated backbone. For some of these applications they are requested to bear polar end groups, and the combination of a chemical inert backbone and a reactive end group can produce peculiar conformations and supramolecular structures. The molecular structure and the vibrational properties of the ethoxyl-terminated PFPE FLUOROLINKE10H in solution are here investigated by means of IR spectroscopy. It is shown that the complex spectral features of the OH-stretching region cannot be explained without a thorough computational study, involving the investigation of the conformational space of an isolated model molecule by means of semiempirical AM1 calculations and DFT calculations. The most relevant conformers were singled out, showing a high degree of conformational disorder for FLUOROLINK E10H. Furthermore, it is shown that intra- and intermolecular H-bonding affects significantly the molecular structure and the vibrational spectrum. Several interactions are shown to be relevant, such as OH. . .F interactions and complexes with residual water. Theoretical values of the absolute intensities of OH stretching IR bands, relevant for the analytical applications, are obtained.