Segmented polyurethanes containing movable rotaxane units on the main chain: Synthesis, structure, and mechanical properties

In this study, segmented polyurethanes (SPUs), including those with rotaxane structures, were synthesized in high yields (>83%) using a [2]rotaxane diol that has a hydroxy group in each wheel and axle component. The traditional prepolymer method was applied to introduce rotaxane structures at different locations in the soft segment and at the boundary between soft and hard segments. The mechanical properties of the formed SPUs were evaluated via tensile tests, and we determined that the introduction of an appropriate amount of rotaxane structure improved their extensibility, toughness, and stress-relaxing properties. Differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR), and synchrotron X-ray measurements revealed that the phase-separated structures of the SPUs were almost independent of the amount of rotaxane. The highly movable rotaxane scaffold was even effective for toughening the SPU, which is a physically cross-linked network, without changing their phase-separated structures.