Room Temperature Photochemical Actuation of A Semi-Crystalline Poly(azobenzene)*

Triggering macroscopic deformation by photochemical molecular configuration changes has been widely studied in the polymer community. A major challenge in this arena is balancing the degree of molecular ordering against the ease of photo-switching and material properties. Typically, materials with higher levels of molecular ordering show more coordinated deformation, thus amplifying microscopic changes to macroscopic level, but usually suffer from difficulties in processing, light-induced fracture, and a lack of photo-switching in the solid state. To help overcome this trade-off, our group developed new crosslinkable semi-crystalline poly(azobenzene)s which provide a high degree of molecular ordering as well as good processability. We have shown the ability to reversibly destroy and restore semi-crystalline order by photo isomerization of azobenzene powered by UV and visible light, respectively. By tuning the chemical structure, and therefore crystalline properties, of the polymers, we show here that photochemical melting/recrystallization can be achieved at room temperature. Aligned fibers of these materials exhibit similar light-induced reversible shape memory properties that were only possible at elevated temperatures with our previously reported polymers.