AbstractInfrared spectroscopy was used to study the structure and deformation behaviour of a series of model poly(ether‐urethane) (PEU) elastomers. These materials contain (molecularly) uniform hard segments obtained from piperazine and the bischloroformate of 1,4‐butanediol with a poly(oxytetramethylene) soft segment and contain no hydrogen bonding. Polarization infrared spectra were obtained simultaneously with stress‐strain measurements during deformation. The orientation of hard and soft segments was measured using static and oscillatory strain. The results are consistent with a lamellar hard‐domain structure in which lamellae orient in the stretching direction at low strain and are sheared apart at higher strains. The stress‐strain and orientation behaviours were found to be highly dependent on the thermal history with annealed samples showing a higher degree of hard‐segment order and resistance to strain‐induced disruption. The PEU samples show an initial rapid and a later gradual relaxation of stress and orientation which occur upon step strain as the hard domains, which are not stabilized by hydrogen bonding, are disrupted under strain. The carbonyl stretching vibration was found to be sensitive to the hard‐segment order. With increasing temperature or strain, an increase in a band component associated with a disordered structure was observed, along with a reduction of the hard‐segment orientation at high strain as the hard domains were disrupted. Under cyclic deformation at 1,6 Hz reversible hard‐segment orientation provides further evidence for lamellar rotation at small strains. Stress‐induced crystallization is obse
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