Arm-replaceable star-like nanogels: arm detachment and arm exchange reactions by dynamic covalent exchanges of alkoxyamine units

Abstract

The arms of star-like nanogels were replaced by means of dynamic covalent exchange processes, and arm detachment and arm exchange reactions were successfully accomplished. Each star-like nanogel with alkoxyamine units at its branching points consisted of arms of poly(methyl methacrylate) (PMMA) synthesized by atom transfer radical polymerization, and a core of poly(divinylbenzene), synthesized by nitroxide-mediated radical polymerization using functionalized PMMA as a macroinitiator. The alkoxyamine groups were capable of serving as radically exchangeable units. Arm detachment reactions were carried out through a radical crossover reaction by heating the star-like nanogels with an excess of a small molecule alkoxyamine, whereas arm exchange reactions were performed by heating nanogels with higher molecular weight PMMA functionalized with alkoxyamine units at the chain ends. The molecular weights and sizes of the star-like nanogels were examined by gel permeation chromatography–multiangle light scattering and small-angle X-ray scattering measurements, respectively, and the shapes of nanogels were characterized by means of scanning force microscopy. Arm-replaceable star-like nanogels consisting of poly(methyl methacrylate) arms and poly(divinylbenzene) cores with alkoxyamine units at their branching points were synthesized by a combination of atom transfer radical polymerization and nitroxide-mediated radical polymerization. The arms of the star-like nanogels were replaced by means of dynamic covalent exchange processes, and arm detachment and arm exchange reactions were successfully accomplished. The structural changes were confirmed by gel permeation chromatography–multiangle light scattering measurements, small-angle X-ray scattering measurements and scanning force microscopic observation.