Intramolecular and intermolecular OH ... O and OH ... F interactions in perfluoropolyethers with polar end groups: IR spectroscopy and first-principles calculations Alberto Milani a,⇑ , Jacopo Zanetti a , Chiara Castiglioni a , Elena Di Dedda a , Stefano Radice b , Giorgio Canil b , Claudio Tonelli b a Politecnico di Milano, Dip. di Chimica, Materiali, Ing. Chimica ‘‘G. Natta’’ – P.zza Leonardo da Vinci, 32-20133 Milano, Italy b Solvay Specialty Polymers R&D Center, Viale Lombardia 20, Bollate (MI) 20021, Italy article info Article history: Received 14 September 2011 Received in revised form 2 November 2011 Accepted 30 November 2011 Available online 8 December 2011 Keywords: DFT calculations Hydrogen bonding Fluoropolymers Vibrational spectroscopy abstract 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 FLUOROLINK Ò E10H in solution are here investigated by means of IR spectroscopy. It is shown that the complex spectral features of the OH-stretch- ing region cannot be explained without a thorough computational study, involving the investigation of the conformational space of an isolated model molecule by means of semi- empirical AM1 calculations and DFT calculations. The most relevant conformers were sin- gled out, showing a high degree of conformational disorder for FLUOROLINK Ò 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 val- ues of the absolute intensities of OH stretching IR bands, relevant for the analytical appli- cations, are obtained. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Since the discovery of polytetrafluoroethylene (PTFE), perfluorinated polymers have been widely known for their superior properties, related to the characteristics of the C–F bonds [1]. Most of these properties, such as high thermal and chemical stability and low glass transition temperature, are shared also by the family of perfluoropolyether (PFPE) fluids: this makes them suitable for advanced applications such as ultrahigh vacuum technologies, advanced lubrica- tion and coating technologies, electronics, etc.; moreover they are used as intermediates in the synthesis of new copolymers. Molecular structure and vibrational properties of several PFPE have been thoroughly investigated in the past [2,3]. The wide range of applications requires the formulation of various classes of PFPE, either completely perfluori- nated, or with polar end groups, or even containing differ- ent monomers (perfluorinated or nonfluorinated) [4]. In this work we analyze the structural and spectroscopic properties of FLUOROLINK Ò E10H, a PFPE with a fluorinated backbone and two chain ends formed by a short (hydroge- nated) ethoxylic chain, bearing a polar OH group. Vibrational spectroscopy (IR and Raman) is one of the main techniques for the investigation of the molecular structure and for the characterization of polymers [5], also 0014-3057/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2011.11.022 ⇑ Corresponding author. E-mail address: alberto.milani@polimi.it (A. Milani). European Polymer Journal 48 (2012) 391–403 Contents lists available at SciVerse ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj