The phase separation of aqueous solutions of poly(N-isopropylactylamide) at different pressures (up to 212 MPa) has been first investigated by high-sensitivity differential scanning calorimetry (IS-DSC). The dependences of the transition temperature, enthalpy and width on pressure have been determined. Upon increasing pressure, the transition temperature passes through a maximum, the enthalpy decreases and the thermodynamic width of the transition notably increases. The transition increment of partial volume of the polymer (Delta(t)v) is found to be positive at low pressures and negative at high ones. The positivity of the increment Delta(t)v points to a significant role of hydrophobic hydration in the transition mechanism. The negativity of Delta(t)v can be related to domination of the interchain H-bond formation upon the system phase separation. The transition width increase reflects changes in the shape of the system binodal. (C) 2015 Elsevier Ltd. All rights reserved.