Control of morphologies and mechanical properties in binary blends of elastomeric polystyrene-BLOCK-polybutadiene-BLOCK-polystyrene triblock copolymers

We report control of morphologies and mechanical properties of elastomeric SBS (polystyrene-block-polybutadiene-block-polystyrene) triblock copolymers by blending two SBS triblock copolymers having different compositions. The microdomain structure was analyzed by the small-angle x-ray scattering technique and the mechanical properties were examined by tensile stress–strain measurements. As a result, it was found that the tensile modulus increases tremendously in the narrow range of composition where the microdomain morphology alters from hexagonally close-packed cylinders to lamellae. Using the Takayanagi model, the parameter (Φ) characterizing the degree of continuity of the glassy polystyrene phase was estimated from the value of the tensile modulus. The variation of Φ with composition exhibits a characteristic feature of a bicontinuous microdomain structure, possibly related to the double gyroid structure. Namely, a remarkable increase in Φ was observed. This implies that the degree of continuity of th...