Synthesis of Iron Oxide-Armored Latex Particles by Pickering Emulsion Polymerization Using 2-Acrylamido-2-methyl-1-propane Sulfonic Acid as an Auxiliary Comonomer

Iron oxide (IO)-armored poly(methyl methacrylate) and polystyrene latex particles have been synthesized by surfactant-free emulsion polymerization using 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) as an auxiliary comonomer. The use of pure water as a dispersion medium led to unstable latexes both in the presence and absence of IO nanoparticles. In stark contrast, successful syntheses were achieved with the addition of ethanol (15 vol % based on water) to the suspension medium. Transmission electron microscopy showed well-defined “armored” structures with the IO nanoparticles located at the latex surface, forming the so-called raspberry-like morphology. The reported strategy allowed the preparation of polymer/IO composite particles with up to 96% IO incorporation efficiency and 60% IO coverage of the latex surface. The effect of the nature of the core monomer and the AMPS and IO contents on the polymerization kinetics, particle size, and morphology was studied in detail. The final nanocomposite particles possess superparamagnetic properties with a high magnetic response, enabling their rapid and efficient separation under an external magnetic field. A mechanism for the formation of the IO-armored latexes is proposed.