Phase separation in aqueous solutions of poly(vinyl methyl ether) was first investigated by high-sensitivity differential scanning calorimetry at normal and high pressures. Thermograms of the phase separation had two singular points: a binodal point (T-t,T-1) and a point of the three phases coexistence (T-t,T-2). At normal pressure the temperature T-t,T-1 decreased slightly and the temperature T-t,T-2 was constant (36.8 +/- 0.1 degrees C) upon increasing the polymer concentration from 0.01 to 0.25%. The transition enthalpy and heat capacity increment did not depend on the polymer concentration (Delta(t)h = 88.0 +/- 1.2 J g(-1); Delta(t)c(p) = -1.0 +/- 0.1 J g(-1) K-1). The calorimetric experiments at high pressures were carried out up to pressure 170 MPa in the range of polymer concentrations 0.1-1.1%. When pressure increased the temperature T-t,T-1 dropped by 10 degrees C, the temperature T-t,T-2 increased by 15 degrees C, the total transition enthalpy reduced 1.5 fold and the transition heat capacity increment remained virtually unchanged. These data reveal that the sequential phase transitions, which the diluted aqueous solutions of poly(vinyl methyl ether) undergo upon heating, have different nature. (C) 2016 Elsevier Ltd. All rights reserved.