Time‐Resolved SAXS/Stress–Strain Studies of Thermoplastic Polyurethanes During Mechanical Cycling at Large Strains

Abstract Simultaneous small‐angle x‐ray scattering (SAXS) and force measurements have been recorded during tensile load/unload deformation cycles of two contrasting polyurethane elastomers. The elastomers comprise the same hard and soft chemical segments; in sample A, the length of the hard blocks is randomized, while, in sample B, the hard blocks are monodisperse. During the initial extension of sample A, the SAXS halo from the mesophase structure deforms to an ellipse with intensification on the meridian. On subsequent loading and unloading, the elliptical halo reverses but with an off‐axis intensification giving the pattern a four‐point character. In sample B, the halo transforms into a four‐point pattern during the first extension. The azimuthal positions of the four‐point maxima move systematically with changing load. However, the azimuthal movement of sample A is in the opposite sense to sample B. The positions of the maxima have been analyzed in terms of an affine deformation scheme of the spatial ...