Crystallization and morphology of poly(arylene ether ether sulfide)s: Dual spherulitic morphology

Abstract

Spherulitic growth rate and morphological studies carried out on a novel poly(ether ether sulfide) yielded dual spherulitic morphologies at all crystallization temperatures. Distinct populations of two kinds of spherulites were formed, with a population of coarse-textured spherulites exhibiting higher growth rate (Type II) than a population of fine-textured spherulites (Type I), at all temperatures studied. The growth rate dependence on temperature for the Type I spherulites was consistent with the theoretically predicted “bell-shaped” curve, indicating nucleation-controlled growth at temperatures close to the melting temperature and diffusion-controlled growth at temperatures closer to the glass transition temperature. The growth rate of the Type II spherulites, however, surprisingly did not exhibit any diffusion-controlled regime, with the growth rate increasing with decreasing temperature across the whole range of temperatures studied here. The above described phenomenon was found to be independent of the prior melt and crystallization history and nature of the substrate in all cases except one. The morphology of the different spherulites has been studied with a combination of optical microscopy, scanning electron microscopy, and atomic force microscopy. The Type II spherulites exhibited a coarser and more “open” morphology, with thicker bundles of fibrils and large interfibrillar gaps, radiating outward from the center of the spherulite. The Type I spherulites were found to exhibit curvature indicative of spherical behavior, whereas the Type II spherulites appeared to exhibit a flat disklike appearance; this finding is consistent with film thicknesses in that samples exhibiting Type I spherulites were films of thickness > 50 μm, whereas Type II spherulites were grown in films of thickness of ∼ 10μm. The differences in the growth rate and morphology between the Type I and Type II spherulites have, thus, been attributed to differences in film sample thickness; the causes behind such effects, however, still remain unclear.