ANOMALOUS 2-STAGE SPHERULITE GROWTH IN POLY(ARYL ETHER KETONES) DURING ISOTHERMAL CRYSTALLIZATION

Anomalous two-stage spherulite growth has been observed in poly(aryl e ther ketones) during isothermal crystallization. The first stage consi sts of a conventional growth with Maltese-cross pattern at a lower gro wth rate. The morphology shows a smooth interface, dense structure and negative birefringence. The second stage grows in the form of ''aggre gate'' at a higher rate. The morphology shows an open dendrite structu re without preferred optical orientation. The second morphology is als o termed the ''overgrowth.'' The occurrence of overgrowth is favored o nly near the maximum growth rate region and diminishes in the slow gro wth region. The transition of the two-stage growth is attributed to th e change of growth direction of the constituent lamellae. We have conf irmed this by microbeam small-angle light-scattering measurements. The lamellar structures in both growth stages were followed by time-resol ved small-angle synchrotron x-ray scattering. It was found that the la mellar structures of the crystals formed at both stages are the same. A possible explanation for the two-stage growth is the interface break down caused by large perturbations of local composition and/or stress fields. (C) 1996 John Wiley & Sons, Inc.