STUDIES ON MORPHOLOGIES AND MECHANICAL PROPERTIES OF POLYSTYRENE-BLOCK-POLYETHYLENEBUTYLENE-BLOCK-POLYSTYRENE TRIBLOCK COPOLYMERS

Abstract

We report the effects of morphologies on mechanical properties of polystyrene-block-polyethylenebutylene-block-polystyrene (SEBS) triblock copolymers using SEBS samples with various compositions. The morphologies and the mechanical properties were examined by the small-angle X-ray scattering (SAXS) technique and the tensile stress-strain measurements, respectively. It is well known that the morphology of microphase-separated structures can be controlled by composition. We found that a border composition dividing spherical and cylindrical phases and that dividing cylindrical and lamellar phases shifted towards smaller values of φ_PS (in the case of φ_PS≤0.5) upon hydrogenation (from SEBS to SBS), where φ_PS denotes the volume fraction of polystyrene and SBS stands for polystyrene-block-polybutadiene-block-polystyrene. Namely, for example, an SEBS sample forms lamellar morphology even at a composition where an SBS sample forms cylinders. It is also confirmed that the mechanical properties were well correlated with change of the morphologies with composition or upon thermal annealing.