Responsive, Structure-Shifting Bottlebrush Copolymer Particles

Structure-shifting polymer particles are of great interest for developing smart soft materials. Here, nanostructured polymer particles capable of switching their morphology in response to external stimuli are presented. The key design is to use a bottlebrush random copolymer with a polydisulfide backbone as a self-assembly building block, in which the polymerization/depolymerization of the dynamic backbone can drive the transformation of the inner particle structure. Nanostructured colloids are generated upon confined assembly of the bottlebrush copolymers in the emulsion droplet, in contrast to the formation of compartmentalized colloids from a blend of polystyrene (PS) and poly(dimethylsiloxane) (PDMS) macromonomers. Exploring the morphology-switching capability reveals that depolymerization of the bottlebrush backbone transforms nanostructured colloids into compartmentalized particles, with intermediate morphologies observed during the depolymerization. Additionally, the morphological transformation is general across multiple inner nanostructures including concentric lamellae, coiled cylinders, and spheres. Importantly, reversible morphology switching capability is realized through polymerization-depolymerization-repolymerization cycles. Finally, the functional potential of these structure-shifting particles is demonstrated by incorporating aggregation-induced emission luminogens (AIEgen). The particles exhibit significant difference in the photoluminescence intensity as a function of particle morphology, attributed to differences in the size of the polymeric domains and the corresponding aggregated state of the luminogens.