Radical crossover reactions of alkoxyamine-based dynamic covalent polymer brushes on nanoparticles and the effect on their dispersibility

The dynamic covalent exchange reactions of side chains in polymer brushes on nanoparticles were successfully demonstrated, and the dispersibility of the nanoparticles after the exchange reactions was investigated in some solvents. A polymer brush with exchangeable alkoxyamine side chains was prepared by surface-initiated atom transfer radical polymerization on silica nanoparticles. Fluorinated and ionic polymers were grafted to the polymer brush via radical exchange reactions of alkoxyamine moieties. The chemical composition of the polymer brushes on nanoparticles before and after the exchange reactions was investigated by X-ray photoelectron spectroscopy (XPS). The XPS measurements indicated that the side chains of the polymer brushes were converted to the corresponding polymers. In addition, the grafted side chains could be detached from the surface of the nanoparticles through a further radical exchange process by treating with alkoxyamines. The XPS results indicate that the structure of the de-grafted polymer brush is nearly the same as the original, thus demonstrating the reversibility of the reactions. Furthermore, the dispersibility of the nanoparticles in solution could be changed by the reversible grafting reactions.