H-1 NMR techniques combined with differential scanning calorimetry (DSC) experiments are employed to investigate the temperature-induced phase transition in aqueous poly(vinyl methyl ether) solutions. NMR data were used to construct van't Hoff plots, and changes in the enthalpy and entropy characterizing the phase transition were determined. It follows from a comparison of NMR and DSC thermodynamic parameters (Delta H values) for solutions with c = 1-30 wt % that the size of the cooperative units (domains) undergoing the transition corresponds to the whole polymer chain.