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The structural development of a segmented poly(urethane-urea) (PUU) elastomer containing a low concentration of hard segment during deformation was studied by simultaneous mechanical and optical measurements (rheooptical techniques). Specifically, in-situ wide-angle X-ray diffraction and smallangle X-ray scattering using synchrotron radiation and time-resolved Fourier transform infrared spectroscopy were applied to investigate the segmental orientation of PUU chains during cyclic elongation and recovery. Formation of two different domain microstructures is characterized with changes in strain. These microstructures consist of lamellar hard domains and highly stressed nanofibrils consisting of alternating hard and crystalline soft domains. By comparing the X-ray scattering and vibrational spectroscopic data, a morphological model of hard-and soft-segment microphase separation, orientation, and strain-induced crystallization in the soft segments was obtained.

The exact value of the wall shear strain is not known. The known quantities are the wall shear stress, the duration for which it is applied and the mass extruded during that time. The flow curve of the polymer at a temperature above the nominal melting temperature is also known, and the time-temperature shift behavior of polypropylene can be applied to the melt. Some of the unknowns that prevent quantitative determination of the wall shear strain are the transient behavior upon inception of non-linear shearing and the development of structures that progressively modify the rheology of the sample due to flow-induced acceleration of crystallization.Here, we give three different estimates of the wall shear strain based on the mass of polymer extruded: a geometical estimate, an estimate based on a Newtonian fluid, and an estimate based on a shear-thinning power-law fluid. All of them assume that steady-state is reached instantaneously and make no attempt to account for the rheology changing with time during shear. The values of the strain, γ ge , reported in our paper are "pseudo"-strains based solely on the geometry of the flow cell. We estimate the strain limit of our instrument as a ratio of the usable length (≈ 5 cm) of the rectangular flow channel to its thickness (0.5 mm) which yields γ ge = 100. Thus, when a mass equal to all the polymer initially in the flow channel [corresponding to a volume of 5cm x 0.635cm