Oligo(ethylene glycol) (OEG) SAMs are important tools in medical applications to hinder the irreversible adsorption of proteins on surfaces. They can be used to structure cells on surfaces or in combination with specific headgroups as sensor elements. The aim of this work was the in-situ characterization of hexa(ethylene glycol) self-assembling monolayers (SAMs), their structural changes at elevated temperatures and their longtime stability. The focus was on the interaction of the thiol molecules with the surrounding water molecules and the conformational and structural consequences. A key to the understanding of the mechanism of protein resistance is the ability of OEG-SAMs to bind water molecules at their surface and in their interior. Infrared spectroscopy is a well suited technique for the identification of molecules and their structural changes due to the interaction with their environment. The surface sensitive polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) technique enables in combination with a thin liquid layer cell measurements under aqueous conditions (in-situ) with a very high signal-to-noise ratio.