Polymer-encapsulated γ-Fe2O3 nanoparticles prepared via RAFT-mediated emulsion polymerization

Abstract

Composite organic/inorganic latexes encapsulating iron oxide (IO) nanoparticles of maghemite (γ-Fe2O3) were successfully synthesized by surfactant-free reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization. γ-Fe2O3 was first dispersed in an aqueous solution containing a statistical copolymer constituted of acrylic acid (AA) and n-butyl acrylate (BA) units, prepared by RAFT polymerization (so-called macroRAFT agent). Taking benefit from the affinity of carboxylic acid groups for iron oxide, the P(AA10-co-BA10) macroRAFT agent was adsorbed onto the surface of IO nanoparticles leading to the formation of macroRAFT/IO clusters. The interaction between the macroRAFT agent and the IO surface was investigated by the study of the adsorption isotherms, indicating that the amount of adsorbed macroRAFT agent increased with increasing macroRAFT concentration. However, a high fraction of the macroRAFT chains (up to 47%) remained in the aqueous phase. The clusters were then engaged in batch emulsion polymerization of styrene or of methyl methacrylate (MMA)/BA mixtures. IO encapsulation was however unsuccessful, and a phase separation between the polymer and the IO clusters was observed. In contrast, semi-batch emulsion polymerization of MMA/BA (90/10 wt ratio) led to effective encapsulation. Morphology studies suggest that the formation of stable latexes containing large IO clusters mainly depends on the concentration of the macroRAFT agent and the pH. Under optimized conditions, a latex with superparamagnetic properties (Ms = 16.2 emu g−1) encapsulating almost all the initial IO nanoparticles was successfully produced.