Shape memory polyurethanes containing azo exhibiting photoisomerization function

A series of azobenzene-containing polyurethanes (azoPU) was synthesized. The structure of the azoPU and the synthesis process were detected by FTIR and nuclear magnetic resonance (NMR), and the transition temperature was determined by differential scanning calorimetry (DSC). Tensile and cyclic thermomechanical experiment results revealed that excellent mechanical properties, shape fixity (R(f)), and shape recovery (R(r)) were obtained by the addition of azo to the chain of PU. R(r) and R(f) of azoPU increased with the increase of hard segment (HS) content. The higher HS content enhanced interaction among polymer chains as the chances of induced dipole-dipole interaction between aromatic rings increased in the presence of azo in the main chain. The materials presented trans-cis isomerization under UV irradiation in addition to the shape memory effect. The UV-vis spectrum indicated that photoisomerization occurred both in solution and solid state. It is expected that the work may be helpful in expanding the application of shape memory PU in areas of drug release and optical data storage.