ABSTRACT:The crystallization behavior of polyamide 66 under high pressure up to 2500 bar was investigated by the use of dilatometric and calorimetric techniques in nonisothermal and isothermal conditions. The solid-solid Brill transition is detected from the evolution of the specific volume in the PVT diagram. The variation of supercooling was examined under different pressures and temperatures. In nonisothermal conditions, when the same cooling rate is applied, the crystallization supercooling is not changed for different pressures. In isothermal conditions, for a given temperature, a pressure increase extends the crystallization supercooling. By the analysis of melting peaks of samples crystallized in different conditions of pressure and temperature, we can conclude that the increasing of the crystallization supercooling leads to a decrease of the lamellae thickness. Finally, the evolution of the thermodynamic equilibrium melting temperature according to pressure was examined.