Strain-Induced Crystallization of Isotactic Polystyrene from the Glassy and ``Rubbery'' States

Abstract

In a continuing effort to extend our understanding of the strain-induced crystallization mechanism we have examined the morphology of oriented isotactic polystyrene (IPS) crystallized from the glassy and ``rubbery'' states under a variety of experimental conditions (elongation, annealing temperature and time, and sample geometry) by means of a wide variety of experimental techniques using Au decorations, solvent etching, electron diffraction, and bright- and dark-field electron microscopy. The oriented morphology is found to be strongly dependent on the original strained state and other experimental variables; it can be either lamellar, fibrillar, or a combination of the two. A fine texture is found to exist in both the lamellar and fibrillar crystals. Extended-chain line nuclei were also sought. Our results, including darkfield studies of highly stretched samples and samples which have been Au decorated or elutriated with solvent, do not reveal any crystallites of length greater than about 100 Å along the stretch direction, thus essentially ruling out their presence in IPS crystallized under strain. The observations are in complete agreement with the strain-induced crystallization mechanism suggested by Yeh and can also account for such phenomena as stress decay and melting temperature increase.