On-demand shape transformation of polymer vesicles via site-specific isomerization of hydrazone photoswitches in monodisperse hydrophobic oligomers

The shape control of nanostructures formed by the solution self-assembly of block copolymers is of significance for drug delivery. In particular, site-specific perturbation resulting in the conformational change of the hydrophobic block has attracted considerable attention because of the possibility of creating polymer vesicles capable of releasing cargo molecules on demand by responding to specific stimuli. Herein, we report the synthesis of amphiphilic block copolymers based on the monodisperse molecular-weight oligo(phenyllactic acid) (OPLA) having hydrazone photoswitches at specific locations. Upon light irradiation, the photoswitch undergoes E-Z isomerization, resulting in the conformational change of the OPLA block. Polymer vesicles composed of these block copolymers exhibited reversible shape transformation upon irradiation with UV or visible light due to the E-Z isomerization of the photoswitch. Furthermore, the location and the number of hydrazone photoswitches in the monodisperse OPLA block are the decisive factors for the reversible shape transformation of the polymer vesicles from an isotropic to an anisotropic morphology.N