The temperature-dependent infrared spectra of water dissolved in carbon tetrachloride containing varying amounts of short-chain poly(oxyethylene) (POE) have demonstrated that an increase of temperature destabilizes bidentate hydrogen bonds between water and POE, and changes them to monodentate hydrogen bonds, which are eventually disrupted at higher temperatures. This process of hydrogen bond breakdown is a possible mechanism, among others, of the phase separation in the POE-water system.