Light-Responsive Crosslinked Polymer Particles from Heterogeneous Polymerization of an Asymmetric Divinyl Azobenzene Monomer

Azobenzene polymer particles have been investigated for over two decades, owing to their interesting light-responsive properties. Crosslinking is a promising solution for improving the reusability of azobenzene polymer particles for practical use; however, the production of crosslinked azobenzene particles remains challenging. In this study, crosslinked azobenzene polymer particles were developed to achieve light responsiveness, recoverability, and reusability. The precipitation polymerization and dispersion polymerization of an azobenzene monomer, ( E )-6-(4-((4-(allyloxy)phenyl)diazenyl)phenoxy)hexyl methacrylate bearing asymmetric divinyl groups, successfully endowed crosslinked azobenzene polymer particles with a unique oblate shape and narrow size distribution. Polarized optical microscope studies indicated that the azobenzene groups were aligned in the particles and had a bipolar configuration. The particles exhibited recoverable light-responsive shape changes upon irradiation with ultraviolet (365 nm) and white light. Hydrophobic and hydrophilic particles prepared by precipitation and dispersion polymerizations yielded water-in-oil and oil-in-water Pickering emulsions, respectively, which were both reversibly formed and deformed upon light irradiation. Furthermore, the reusability of the particles in light-responsive liquid marbles was achieved. Consequently, the asymmetric divinyl azobenzene monomer successfully produced recoverable and reusable light-responsive polymer particles.