Photoinduced Motions of Thermoplastic Polyurethanes Containing Azobenzene Moieties in Main Chains

Thermoplastic
polyurethane containing azobenzene moieties in main
chains was developed for photomobile materials capable of reversible
photoactuation and shape programming, and was characterized for phase
transition properties, microstructures, and photoinduced deformation
behaviors. Photomobile films with glassy nature could be fabricated
using both melt- and solution-processing methods, in contrast with
conventional photomobile materials consisting of chemically cross-linked
networks. The alignment of azobenzene moieties and macroscopic shapes
in the initial states were controlled by external force under heating
above glass transition temperature, which were stabilized by the formation
of physical cross-links through hydrogen bonding interactions. The
films with uniaxial alignment of azobenzene moieties showed reversible
bending upon irradiation with UV and visible light, which could be
repeated for 100 cycles. Physical cross-links in the present system
can be an alternative for covalent cross-links in photomobile polymer
materials, expanding the variety of designs with superior processability.