Stepwise Grafting of Polymer Single Chains onto Nanoparticles

It is important to design hierarchically structured functional polymer/inorganic composite nanoparticles (NPs) and self-organize them toward programmable superstructures thereby. We propose the synthetic approach of stepwise grafting anionic polymer single chains onto functional nanoparticles via termination, which is ensured by the strong steric hindrance effect of the grafted chains to the target chains with a comparable size. The concept is demonstrated by the precision synthesis of NP-inserted diblock copolymer analogies of PVSt-b-PmSt-[Fe3O4@SiO2]-PMMA-b-PtBA with two different polymer single chains at the opposite sides (PVSt-b-PmSt: poly(4-vinylphenyl-1-butene)-block-poly(4-methylstyrene), PMMA-b-PtBA: poly(methylmethacrylate)-block-poly(tert-butyl acrylate)). Both end segments of PVSt and PtBA are reactive to derive functional groups such as amino and carboxylic acids by the orthogonal clicking reaction and hydrolysis. The functional groups allow visualization of the composite NPs by stimulated emission depletion (STED) microscopy upon selective fluorescence dyeing and the self-organization by specific interactions toward superstructures at varied pHs. The approach is valid for the stepwise grafting of six single chains of varied compositions along the three-dimensional coordinate. The composite NPs with defined numbers and types of functional groups, and thus interaction directions, provide a huge platform for diversifying superstructures, especially under external fields.