The aim of this thesis was to investigate the water binding in aqueous solutions of poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG) and amphiphilic symmetric triblock copolymers of PEG and PPG by water activity measurements as function of temperature and concentration. Furthermore, Differential Scanning Calorimetry (DSC) was used to determine the critical micelle temperature (cmt) of the triblock copolymers. Eight different PEG polymers, one PPG polymer and three different triblock copolymers were applied; however the PPG polymer was omitted as it could not be dissolved properly. The water activity measurements showed that the water activity increases with increasing temperature and decreasing concentration, i.e. water becomes a poorer solvent with increasing temperature because the polymer-water interactions are reduced. Excess enthalpies for the water binding were derived from the water activity measurements, but these are too large due to insufficient equilibrium time in the system. The DSC measurements showed that at a given concentration the cmt increases with increasing hydrophilicity of the copolymer.