Self-assembly and degradation of photolabile diblock bottlebrushes

Aqueous self-assembly of amphiphilic block copolymers form diverse nanostructured morphologies depending on block volume fraction and solvophilicity. Stimuli-responsive motifs have been combined with self-assembled micelles to afford spatiotemporal, on-demand encapsulation and payload release. However, the role of modular polymer architecture (i.e., bottlebrushes) in stimuli-responsive aqueous self-assembly is not fully understood. The synthesis, aqueous self-assembly, and photoirradiation of photolabile, amphiphilic bottlebrush block copolymers is presented herein. Specifically, the efficient photoscission of o-nitrobenzene motifs at the junction of a poly(norbornene o-nitrobenzene polystyrene)-block-poly(norbornene polyethylene glycol) diblock bottlebrush side chain and backbone cleaved away hydrophobic polystyrene side chains and artificially increased the volume fraction of poly(ethylene glycol) (f_PEG). In doing so, self-assembled micelles readily degrade to micelle-to-micelle and micelle-to-aggregate structures after photoirradiation. Finally, this bottlebrush micelle system is used to demonstrate the efficient encapsulation and stimuli-responsive release of Nile Red that is monitored by fluorescence spectroscopy and dynamic light scattering. The contribution of this work expands the utility of amphiphilic bottlebrush systems as highly efficient and responsive, hierarchically assembled nanomaterials.