Multiple melting behavior in isothermally cold-crystallized isotactic polystyrene

The multiple melting behavior and lamellar morphologies of isotactic polyst yrene (iPS) isothermally crystallized from the glassy state have been inves tigated by differential scanning calorimetry (DSC) and transmission electro n microscopy (TEM). The influences of different experimental variables (suc h as crystallization temperature and time, heating rate) on the melting beh avior of iPS are studied. The combination of thermal analysis and morpholog ical results indicates that: (1) the 'annealing peak' is not associated wit h the melting of subsidiary crystals formed by secondary crystallization as often suggested in the literature; (2) two lamellar populations with diffe rent degrees of perfection within a single lamella are responsible for the so-called double melting behavior in iPS. The partial melting and repairing (via recrystallization) of iPS crystals are observed on lamellar level by TEM observations. From the obtained calorimetric and morphological results, the applicability of several crystallization and (subsequent) melting mode ls is discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.