Study of the thermodynamics of the melting and kinetics of isothermal crystallization of isotactic polypropylene at raised pressures

Abstract Volumetric dilatometry under pressure has been employed to investigate the dependence of the temperature and enthalpy of melting, the crystallization rate and the energy parameters of nucleation of polypropylene on hydrostatic pressure on crystallization from the melt. An abrupt fall was found in the free surface energy of the end phases of the crystallization seeds with fall in pressure from 30 to 20 MPa considerably increasing the rate of crystallization of the polymer from the melt. The phenomenon observed is due to passage of the macromolecules from a folded to a more straightened conformation in the crystal (topomorphism).