The spherulitic structure of crystalline polymers. Part I. Investigations with the polarizing microscope

Abstract

An investigation on polymer spherulites is being described in three parts. Part I (the present paper) describes the various effects observed under the polarizing microscope. These are interpreted in terms of the concepts of crystal optics; the problem of the position of the molecules and that of the microscopic fine structures will form Parts II and III. The materials examined were: polyethylene terephthalate, polyhexamethylene sebacamide and adipamide, and polyethylene. It is confirmed that the growing spherulites are a crystalline part of the crystallizing melt, and their individuality is demonstrated. The spherulites are radiating fibrous structures and the various observed extinction effects were interpreted in terms of such fibrous units. These extinction effects varied with the different materials and also for a particular substance with conditions of crystallization. Apart from the usual Maltese crosses, zigzag and ringshaped extinction lines were observed between crossed Nicols. The zigzag lines were interpreted as resulting from the index ellipsoids lying along elongated helical paths, while the most plausible explanation of the rings is given by closely coiled or strongly twisted arrangements of the index ellipsoids. The possibility of the existence of helical structures in spherulites is discussed in the light of earlier work on spherulites of simple substances.