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

A morphological study was performed with symmetric diblock ethylene-propylene copolymer (DEP) and the binary blends made from DEP and atactic polypropylene (APP) by use of small angle X-ray, light and neutron scattering, and also scanning and transmission electron microscopy. DEP contains a crystallizable polyethylene block and an amorphous atactic polypropylene block. Quenching the blends in liquid nitrogen preserved the morphology in the melt state. This quenching technique revealed that DEP forms a lamellar microdomain structure and blending DEP and APP includes morphological changes in the microdomain structures as well as macrophase separation. When the APP chain was shorter than the APP block, the addition of APP changed the morphology from a lamellar to a bicontinuous cylindrical and then a discrete cylindrical and finally to a spherical structure. On the other hand, when the APP chain was longer than the APP block, macrophase separation was observed and only a transition from a lamella to a bicontinuous cylinder occurred. These morphological transitions in the melt state can be correlated to differences in the crystallization kinetics of the blends. Copyright (C) 1996 Elsevier Science Ltd.