Thermoplastic Azobenzene Polyurethanes with Both Efficient Photomediated Migration and Excellent Mechanical Strength

Azobenzene polymers with efficient photomediated migration are highly desired because of their potential application in sensors, actuators, and information storage devices. Various methods have been developed to improve photosensitivity of azobenzene polymers; however, performances of the reported polymers so far are still less than satisfactory. While azobenzene polymers of high glass transition temperature (Tg) or melting temperature (Tm) are usually of practical use, photomigration in high Tg (or Tm) azobenzene polymers is difficult because polymer chains are frozen at low temperature. Here, we report the preparation of thermoplastic azobenzene polyurethanes (azo TPUs) with both efficient photomediated migration and excellent mechanical performances. These TPUs are in the phase-separated state with hard microdomains of high Tm embedded in a soft matrix of low Tg. Because of their high Tm, these azo TPUs are mechanically strong with maximum stress exceeding 8 MPa. However, as a result of the two-phase design with the majority of materials being a soft component with low Tg, these azo TPUs also show efficient photomigration of micrometers under UV irradiation (125 mW/cm2, 160 s) despite their high Tm. At higher amplitude of UV light (>500 mW/cm2) and in the presence of a photothermal effect, rare macroscopic mass transportation of centimeter was observed. These azo TPUs may find application in actuators, optical information storage devices, or as optical healable materials.