Thermal- and light-responsive programmable shape-memory behavior of liquid crystalline polyurethanes with pendant photosensitive groups

Abstract

In this study, a liquid crystalline polyurethane that exhibits thermal- and light-responsive programmable shape-memory behavior was prepared via the quaternization reaction between a mesogenic azobenzene compound and a conventional polyurethane (PU). In the film, the variation in the configuration of mesogenic azobenzene units afforded the internal stress to actuate the motion of the polymer chains and induced the chains to adopt a coiled conformation, leading to the macroscopic deformation of the film under light stimulation. The hard segments of PU provided the skeleton that froze the conformation of the polymer chains and ensured that the temporary shape was maintained after removing the stimuli. The variation of the tensile stress required for maintaining the elongation of the film under different stimuli was measured, and a possible mechanism for the multiple stimuli-responsive shape deformation of the material from the point of view of the evolution of polymer chain conformations was also discussed. Moreover, flexible photomechanical devices based on the liquid crystalline polyurethane film were fabricated, and the soft devices could catch an object even in the absence of stimuli. This work can provide a creative route for the fabrication and practical application of novel photomechanical devices and soft robotics more in line with the requirements of energy-saving and intelligence.