Highly water-dispersed superparamagnetic magnetite colloidal nanocrystal clusters from multifunctional polymeric nanoreactors: synthesis and properties

Abstract

An unconventional but robust strategy to fabricate uniform hybrid inorganic–organic core–shell superparamagnetic magnetite (Fe₃O₄) colloidal nanoclusters in situ was introduced based on water-soluble multi-arm star-shaped brush-like block copolymers as multifunctional polymeric nanoreactors, composed of poly(ethylene oxide) (PEO) as the main chain, poly(acrylic acid) (PAA) as functional graft chains, and the second PEO block as a shell (i.e., multi-arm star-shaped brush-like block copolymer [(PEO-g-PAA)-b-PEO]₁₈) with different molecular weights and grafting densities. FeCl₃ and FeCl₂ as precursors of Fe₃O₄ were loaded into the graft chain PAA template domain of a multi-arm star-shaped brush-like block copolymer [(PEO-g-PAA)-b-PEO]₁₈ polymeric nanoreactors, followed by an in situ reaction to form Fe₃O₄ nanoclusters. The dimensions of the clusters can be tuned precisely by changing the chain lengths of the PEO backbones of the PAA grafting region. In addition, the density of the subunits can also be tailored by adjusting grafting density of the PAA side chains, determined by the molar ratio of ethoxyethyl glycidyl ether (EEGE) to EO during the anionic copolymerization. The Fe₃O₄ colloidal nanocrystal clusters with superparamagnetic behavior at room temperature are highly water-dispersed because of the hydrophilic ligands of the surface-tethered PEO polymer shell.