Coupled Photoisomerization, Chain Reorientation, and Shape Deformation in Main-Chain Azobenzene Polymer Particles Prepared by Heterogeneous Radical-Mediated Thiol–Ene Polyaddition

Main-chain azobenzene polymers provide a unique platform in which photoisomerization is directly coupled to backbone conformation and molecular ordering. Herein, we report the synthesis of noncrosslinked main-chain azobenzene polymer particles by heterogeneous radical-mediated thiol–ene polyaddition of a divinyl azobenzene and a dithiol. Particle formation proceeded through polymerization-induced liquid–liquid phase separation followed by solidification, revealing characteristic features of particle formation in this step-growth polymerization system. The resulting particles developed ordered internal structures, whose domain configurations were controllable by thermal treatment. Photoisomerization of the azobenzene units induced changes in chain conformation, altered chain ordering, and enabled shape changes of mechanically deformed particles. These findings establish heterogeneous radical-mediated thiol–ene polyaddition as a molecular-design strategy for propagating azobenzene photoisomerization into backbone conformational, structural, and mechanical responses in polymer particles.