SYNTHESIS AND CHARACTERIZATION OF SEMICRYSTALLINE POLY(AZOBENZENE) FOR NEXT GENERATION PHOTOMECHANICAL EFFECTS

Photomechanical materials powered by light-induced changes in crystalline lattices offer promise for improved performance due to the high degree of coordination between the shape changes of individual molecules. While photoswitchable semicrystalline polymers present an attractive combination of molecular ordering and material processability, systems developed to date typically have some fundamental limits hindering the photomechanical performances. To this end, this dissertation explores strategies to resolve several major challenges in efficient and effective semicrystalline photo-actuators. Chapter 2 describes the temperature dependence in photostationary state conversion and photochemical kinetics of photoswitching P(C6-azo) and generalizing such temperature dependence to other main-chain semicrystalline poly(azobenzene)s. Chapter 3, we take one step further to prepare a semicrystalline poly(azobenzene) containing an ethylene glycol chain extender, denoted as P(EG-azo). Because of its backbone flexibility, P(EG-azo) shows lower Tg and Tm, enabling rapid and thorough photomelting and photocrystallization at room temperature with high reversibility, useful for low/ambient temperature applications. In Chapter 4, the reversible photo-induced phase transition of P(EG-azo) is used to enable photoswitchable ionic conductivity with high on/off ratio of ionic conductivity switch, which shows great promise for optoelectronic applications. In Chapter 5, structurally modified azobenzene photochrome with tetra-ortho-substitution is incorporated into the semicrystalline polymer backbone. With distinct n − π∗ transition peaks from both isomers, near-quantitative photoswitching with visible light and ”negative photochromic effect” have been demonstrated. Lastly, in Chapter 6, an outlook for a possible future directions to further improve photomechanical effect is presented