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 degreesC (above the glass transition temp erature of polystyrene; T-g(PS)) The lamellar orientation was examined usin g two-dimensional small-angle X-ray scattering (2d-SAXS) experiments. It wa s revealed that the lamellar normal preferentially oriented perpendicular t o the stretching direction such that the microdomain interface between poly styrene and polybutadiene lamellae is more or less parallel to the stretchi ng 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 T -g(PS)) without the lamellar orientation. Therefore, it is concluded that t he strain-induced orientation of lamellae can be only attained above Tg(PS) and that the uniaxial stretching above T-g(PS) was found to be an effectiv e way to induce the preferential orientation of lamellae. The lamellar orie ntation was found to be improved by the thermal annealing at a stretched st ate and more by increasing the extent of the stretching, as well as cross-l inking density.