Preferential Orientation of Lamellar Microdomains Induced by Uniaxial Stretching of Cross-Linked Polystyrene-block-polybutadiene-block-polystyrene Triblock Copolymer

We report an experimental result for a lamellar orientation in cross-linked polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymer that was uniaxially drawn at 130 °C (above the glass transition temperature of polystyrene; Tg(PS)). The lamellar orientation was examined using two-dimensional small-angle X-ray scattering (2d-SAXS) experiments. It was revealed that the lamellar normal preferentially oriented perpendicular to the stretching direction such that the microdomain interface between polystyrene and polybutadiene lamellae is more or less parallel to the stretching direction, where the lamellar normal denotes the direction normal to the lamellar interface. On the other hand, a herringbone structure was induced by the uniaxial stretching for a sample drawn at room temperature (below Tg(PS)) without the lamellar orientation. Therefore, it is concluded that the strain-induced orientation of lamellae can be only attained above Tg(PS) and that the uniaxial stretching above Tg(PS) was found to be an effective way to induce the preferential orientation of lamellae. The lamellar orientation was found to be improved by the thermal annealing at a stretched state and more by increasing the extent of the stretching, as well as cross-linking density.