THE COMPETITION BETWEEN CRYSTALLIZATION AND PHASE-SEPARATION IN POLYMER BLENDS .2. SMALL-ANGLE X-RAY-SCATTERING STUDIES ON THE CRYSTALLINE MORPHOLOGY OF POLY-(EPSILON-CAPROLACTONE) IN ITS BLENDS WITH POLYSTYRENE

The courses of crystallization and of demixing or mixing, respectively, can interfere and compete in polymer blends with a miscibility gap. Crystallization dominates at lower temperatures, possibly inhibiting rejection of the non-crystallizing component into the remaining melt and enhancing its concentration in the amorphous regions between the crystalline domains. Time-resolved small-angle X-ray scattering measurements on poly(epsilon-caprolactone)/polystyrene (PCL/PS) blends, this system exhibiting an upper critical solution temperature, reveal that the amorphous regions between the lamellae within the PCL spherulites nearly do not phase separate when passing the binodal composition. Instead, supersaturation of composition occurs. The initially bent lamellae flatten with time, and the supersaturated spherulite amophous phase post-crystallizes according to the insertion crystallization scheme on a timescale that is comparable to the overall crystallization rate.