Mechanisms of Directional Polymer Crystallization

Zone annealing is adapted here to crystalline polymers. Almost 50 years ago, Lovinger and Gryte postulated that for a polymer undergoing zone annealing, at steady state, the crystal growth rate of the polymer equals the velocity at which the sample is being pulled through the temperature gradient. They also implied that there is a critical velocity below which the crystal growth rate dominates over nucleation, and that directional crystallization can therefore only occur below this critical velocity. In this work, we perform analyses of SAXS, DSC, and CPOM of zone annealed PEO in order to examine these postulates. The steady-state ansatz is validated with our long period data, and an analysis of Herman’s orientation function shows that there exists a transitional region around a critical velocity where a coexistence of oriented and isotropic domains occurs. Below this critical velocity, directional crystallization is achieved, while above it, the mechanism is more similar to that of conventional isotropic isothermal crystallization.