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Segment and domain orientation behaviors of a series of poly(butylene succinate) (PBS) -poly(tetramethylene glycol) (PTMG) segmented block copolymers containing different amounts of hard segment were studied with synchrotron smallangle X-ray scattering (SAXS) and infrared dichroic methods. Copolymers used in this work consist of PBS as a hard segment, and poly(tetramethylene oxide) (PTMO) of molecular weight 2000g/mol as a soft segment. As hard-segment content increased, phase-separated morphology changed from a phase of continuous soft matrix containing isolated hard domain to one of continuous hard matrix. Upon stretching, domains responded differently depending on their initial orientation. Based on SAXS results, two major domain deformation modes, that is, lamellar separation and shear compression, were suggested. The orientation behavior of the hard and soft segments was examined with infrared dichroic method. Upon drawing, the orientation function of the crystalline hard segment decreased at low-draw ratios. It was interpreted in terms of rotation of long axis of hard domain along the stretching direction. The lowest value of the orientation function of PBS30 was approximately Ϫ0.5, that is, theoretical minimum. This result seems to indicate that for PBS30 containing about 30% hard segment, rotation of hard domain occurs without appreciable interdomain interaction, which is consistent with the morphological model suggested on the basis of SAXS results. Plastic deformation of the hard domain due to domain breakup was found to occur at low-draw ratios for the sample containing higher hard-segment content. Domain mechanical stability was tested by drawing a sample up to three different maximum draw ratios.