Mixed polymer brushes are an intriguing class of surface responsive materials that have been shown to exhibit distinct morphologies under different conditions. When these brushes are grafted on nanoparticles (NPs), the substrate curvature is expected to affect their self-assembled morphologies. Although simulation studies have shown a variety of unique nanostructures formed from mixed brush-grafted small NPs and have suggested a route for the fabrication of multivalent patchy NPs with well controlled number and locations of functional sites, little experimental work has been reported. By immobilizing an asymmetric difunctional initiator (Y-initiator) onto small silica NPs, we have successfully synthesized mixed poly(<i>tert</i>-butyl acrylate)/polystyrene brushes on small NPs with high grafting densities, precisely controlled molecular weights, and narrow dispersities through sequential surface-initiated atom transfer radical polymerization (ATRP) of <i>tert</i>-butyl acrylate and nitroxide mediated radical polymerization (NMRP) of styrene. ATRP and NMRP are two different “living”/controlled radical polymerization techniques, allowing for tuning of the molecular weights of the two grafted polymers independently. Transmission electron microscopy studies reveal that the mixed brushes grafted on small NPs undergo lateral microphase separation when cast from chloroform, resulting in distinct truncated wedge-shaped nanostructures. In contrast, mixed brushes that are grafted on much larger particles self-assemble into more uniform nanostructures.

Well-defined binary mixed homopolymer brushes grafted on small nanoparticles

ACS Fall 2021

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