Blends of amorphous-crystalline block copolymers with amorphous homopolymers. Morphological studies by electron microscopy and small angle scattering

Abstract

A morphological study was performed with symmetric diblock ethylene-propylene copolymer (DEP) andthe binary blends made from DEP and atactic polypropylene (APP) by use of small angle X-ray, lightand neutron scattering, and also scanning and transmission electron microscopy. DEP containsa crystallizable polyethylene block and an amorphous atactic polypropylene block. Quenching the blendsin liquid nitrogen preserved the morphology in the melt state. This quenching technique revealed that DEPforms a lamellar microdomain structure and blending DEP and APP includes morphological changes in themicrodomain structures as well as macrophase separation. When the APP chain was shorter than the APPblock, the addition of APP changed the morphology from a lamellar to a bicontinuous cylindrical and then adiscrete cylindrical and finally to a spherical structure. On the other hand, when the APP chain was longerthan the APP block, macrophase separation was observed and only a transition from a lamella toa bicontinuous cylinder occurred. These morphological transitions in the melt state can be correlatedto differences in the crystallization kinetics of the blends