A Multiphase Model Describing Polymer Crystallization and Melting

Abstract

The results of temperature dependent small angle X-ray scattering experiments on a variety of crystallizing polymers contradict conventional wisdom and suggest that polymer crystallization generally uses a route which includes a passage via a mesomorphic phase. We construct a thermodynamic scheme dealing with the transitions between melt, mesomorphic layers and lamellar crystallites, assuming for the latter ones that they exist both in an initial ‘native’ and a final ‘stabilized’ form. Application of the scheme in a quantitative evaluation of small angle X-ray scattering and calorimetric results yields the equilibrium transition temperatures between the various phases, latent heats of transition and surface free energies. As an example, the data obtained for s-polypropylene are given. Here, the mesomorphic phase has thermodynamic properties which place this state intermediate between melt and crystals.