EFFECTS OF MORPHOLOGY ON MECHANICAL-PROPERTIES OF A SBS TRIBLOCK COPOLYMER

The morphology and mechanical properties of the mouldings of a poly(styrene-block-butadiene-block-styrene) triblock copolymer (KR05, Phillips Petroleum Co.) were examined. All the mouldings exhibit lamellar morphology and their mechanical properties depended on the lamellar orientation. KR05 with oriented lamellae shows excellent Izod impact strength and large elongation since under tensile stress the lamellae shear yield extensively with dominant expansion and cavitation of the polybutadiene lamellae. That with wavy lamellae shows enhanced rigidity and heat resistance since the lamellae also shear yield but offer more resistance against the deformation because of the close and complicated networks of the polybutadiene phase with the rigid polystyrene phase. Stereoscopic structural examination of the mouldings revealed that the appreciable mechanical anisotropy results from the anisotropy of the microdomain structure formed on cooling the melt.