Surfactant-Free Emulsion Polymerization Stabilized by Ultrasmall Superparamagnetic Iron Oxide Particles Using Acrylic Acid or Methacrylic Acid as Auxiliary Comonomers

Abstract

Iron oxide (IO)-based composite latex particles with a patchy IO overlayer were successfully prepared by Pickering emulsion polymerization of acrylic monomers and/or styrene using acrylic acid or methacrylic acid as auxiliary comonomers. The ultrasmall IO particles adsorbed at the latex surface and played the role of a solid stabilizer. The influence of the synthesis conditions on the composite particle size, polymerization kinetics, IO incorporation efficiency and particle morphology was studied. Thermogravimetric analysis indicated that the efficiency of iron oxide incorporation was improved with increasing the suspension pH, the amount of auxiliary comonomer or the IO content, and reached ca. 90% under optimized conditions. Reducing the initial iron oxide concentration at constant monomer concentration led to an increased particle size and a reduced colloid stability, indicating that the magnetic nanoparticles stabilized the colloidal nanocomposites. Transmission electron microscopy studies confirmed the presence of iron oxide at the particle surface. In the light of these results, a tentative mechanism for Pickering emulsion polymerization using IO nanoparticles as solid stabilizer in the presence of (meth)acrylic acid auxiliary comonomers was proposed.

A mechanistic investigation of Pickering emulsion polymerization

“…The use of water as continuous phase has environmental benefits, and the dual nature of these particles allows for performance enhancement of application products such as coatings and adhesives. For instance, hybrid particles can add magnetic response [1][2][3] and improve flame retardant and mechanical properties of dried films. 4,5 Furthermore, poly(lauryl acrylate) latex particles armoured with Laponite clay discs have been shown to increase the tack adhesion of pressure-sensitive adhesives, when used as additive.…”

Surfactant-free synthesis of layered double hydroxide-armored latex particles

“…A similar behavior was reported by Teixeira et al 24 during Pickering emulsion copolymerization of n-butyl acrylate and MMA using LAPONITE® clay as stabilizer, and was ascribed to in situ MMA hydrolysis. The deleterious effect of a too high concentration of the auxiliary comonomer was also emphasized by Li et al 29 during the synthesis of IOarmored latexes. As shown in Fig.…”

“…Previous works on Pickering emulsion polymerization using various types of inorganic nanoparticles, have shown that latex stability and final particle morphology strongly depend on the physicochemical properties of the mineral and the nature and composition of the monomer mixture. 29 According to Lotierzo et al, 22 inorganic particles do not spontaneously adsorb onto the surface of latex particles in the absence of external attractive forces. The authors argued instead that oligoradicals formed Table 1).…”

“…Our group also recently described the surfactant-free synthesis of composite latex particles with a patchy IO overlayer through Pickering emulsion polymerization of St and (meth)acrylates, using (meth)acrylic acids (MAA or AA) as auxiliary comonomers. 29 A minimum amount of auxiliary comonomer was required to favor IO adsorption at the latex particle surface, while a too high concentration promoted IO aggregation and latex destabilization. Other workers reported the use of poly(ethylene glycol)-based macromonomers (PEGMA or Sipomer PAM) to favor adsorption of silica 21 or LAPONITE® clay platelets 9,23 at the surface of Pickering latex particles.…”

“…Until now, a large variety of inorganic nanoparticles has been investigated as solid stabilizers in Pickering emulsion polymerization, such as colloidal silicas, [16][17][18][19][20][21][22] LAPONITE® clay discs, 4,9,[23][24][25][26][27] iron oxide nanoparticles, 28,29 zinc oxide, 30,31 cerium dioxide 7 and titania. [32][33][34][35] To promote the effective adsorption of the Pickering stabilizer onto the polymer latex particles, several strategies have been reported.…”