STRUCTURE AND PROPERTIES FOR BINARY BLENDS OF ISOTACTIC-POLYPROPYLENEWITH ETHYLENE-ALPHA-OLEFIN COPOLYMER .1. CRYSTALLIZATION AND MORPHOLOGY

Morphology and isothermal growth rates of spherulites for the binary b lends consisting of an isotactic polypropylene (i-PP) and an ethylene- l-hexene rubber (EHR) were examined as a function of the crystallizati on temperature ranging from 388 K to 418 K. In this study, two types o f EHR's were employed: ''ethylene rich'' EHR and ''1-hexene rich'' EHR . The blends of i-PP with the EHR of 51 mol % l-hexene are miscible in the molten state, whereas the blends with the EHR of 33 mol % l-hexen e are immiscible in the molten state. It is found that the isothermal spherulite growth rate of the miscible i-PP/EHR blends decreases with increasing the EHR fraction, whereas the spherulite growth rate of the immiscible i-PP/EHR blends is independent of the blend composition an d is the same as that of the i-PP. Optical microscope observation of t he miscible blends crystallized isothermally shows that there are no r ubber domains either in the intraspherulitic or in the interspheruliti c contact regions. On the other hand, the immiscible i-PP/EHR blends s how a phase-separated morphology. Furthermore, the number of tangentia l lamellae of the miscible i-PP/EHR blends is found to be increased by blending of the EHR, leading to the spherulite with negative birefrin gence. The sign of birefringence of spherulites is unaffected by the r egime transition as well as by the fold surface free energy. (C) 1997 John Wiley & Sons, Inc.