Synthesis of azobenzene-containing liquid crystalline block copolymer nanoparticles: Via polymerization induced hierarchical self-assembly

Polymerization induced hierarchical self-assembly (PIHSA), combining liquid crystallization and polymerization induced self-assembly, is a facile approach to synthesize block copolymer (BCP) nanoparticles (NPs) with non-spherical morphologies. Herein, a PIHSA formulation based on azobenzene-containing poly(N,N-dimethylaminoethyl methacrylate)-b-poly (11-(4-(4-butylphenylazo) phenoxy) undecyl methacrylate) (PDMAEMA-b-PMAAz) BCPs was developed by reversible addition-fragmentation chain-transfer dispersion polymerization in n-butanol at 10% w/w solid content. According to the dispersion polymerization kinetics, a relatively high monomer conversion of ∼95% was achieved within 11.5 h. The morphology evolution was investigated in detail by tuning the chain length of PDMAEMA and feed ratio of MAAz/PDMAEMA. A morphology phase diagram was constructed. Non-spherical morphologies, especially one-dimensional morphologies, occupied a remarkable phase region due to the liquid crystallization of the azobenzene-containing core-forming block. Taking advantage of the photo-isomerization properties of azobenzene moieties, the NPs underwent morphological transformation upon alternate UV/Vis irradiation. This work expands the PIHSA systems and would be helpful for potential applications, such as coating, smart devices, and gene delivery materials.