Multilayered composite microgels synthesized by surfactant-free seeded polymerization.

We report on a simple and rapid method to produce multilayered composite microgels. Thermosensitive microgels were synthesized by aqueous free radical precipitation polymerization using N-isopropylacrylamide (NIPAm) as a monomer. Using the microgels as cores, surfactant-free seeded polymerization of an oil-soluble monomer, glycidyl methacrylate (GMA), was carried out at 70 °C, where the microgels were highly deswollen in water. All of the oil-soluble monomers were polymerized, and the resultant polymers were attached on the pre-existing microgel cores, resulting in hard shell formation. It is worth mentioning that secondary particles of oil-soluble monomers have never been formed during the polymerization. The composite microgels were characterized by electron microscopy and dynamic light scattering. In particular, X-ray photoelectron spectroscopy (XPS) measurements revealed that the surface of the composite microgels was composed of a hydrogel layer, although microgel cores were covered by polyGMA shell. The mechanism of the trilayered composite microgel formation will be discussed.