Photoinduced Reversible Worm-to-Vesicle Transformation of Azo-Containing Block Copolymer Assemblies Prepared by Polymerization-Induced Self-Assembly

A series of azo-containing copolymeric assemblies based on poly(N,N-dimethylaminoethyl methacrylate)-b-poly[(benzyl methacrylate)-co-(4-phenylazophenyl methacrylate)] [PDMA-b-P(BzMA-co-AzoMA)] were prepared by reversible addition–fragmentation chain transfer polymerization-induced self-assembly at high solid contents. Depending on the chain length of P(BzMA-co-AzoMA), spheres, worms, and vesicles were readily prepared. These azo-containing wormlike micelles underwent reversible worm-to-vesicle transformation upon alternative UV/vis light irradiation. By investigating the morphology evolution, a series of intermediates were observed, including coalesced worms as well as "octopus"-like and "jellyfish"-like structures. The morphology transformation was rationalized by the volume change of the P(BzMA-co-AzoMA) block caused by the trans–cis isomerization of the azobenzene groups. It is the first demonstration of light-stimulated reversible worm-to-vesicle transition and would benefit for the understanding of morphology evolution of polymer assemblies under external stimuli.