Melt memory effects in polymer crystallization

Polymer melts submitted to local shear flow fields, as well as isotropic solid samples, were treated in the melt at different temperatures and for various duration of time. The effects of thermal history on kinetics and morphological characteristics of subsequent isothermal crystallization was investigated. Results suggest that subcritical pseudocrystalline aggregates, behaving as predetermined athermal nuclei when temperature is brought below melting point, can survive in the melt for long time. Their concentration decays exponentially with a single characteristic relaxation time. For all investigated polymers, temperature dependence of relaxation times can be fitted by an Arrhenius law with high apparent activation energy. Experiments performed with narrow molecular weight fractions of poly(ethylene oxide) suggest that relaxation times relevant to destruction of oriented nucleation precursors are proportional to M-1.5.