A small-angle X-ray scattering study on styrene-butadiene-styrene block copolymers during stretching is reported. Measurements have been performed at the Hamburg Synchrotron Radiation Laboratory at DESY using a two-dimensional position-sensitive detector. A pattern of layer lines perpendicular to the stretching direction with ellipsoidal envelope is obtained. This indicates a good orientation of cylindrical polystyrene domains along the stretching direction. The diameter-to-length ratio of the cylinders was found to be 0.6, the length being approximately 39 nm. The long period of the undrawn sample is about 47 nm. Upon stretching, initially this value increases almost affinely, while for γ>3 it tends to reach a constant value. The extension at which the curve bends coincides with the inflection point in the stress-strain curve; at higher values of extension, most of the polybutadiene chains are probably completely stretched and further extension is achieved partly by disruption of the polybutadiene matrix. © 1990.
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