Synthesis and Characterization of Silica/Poly (Methyl Methacrylate) Nanocomposite Latex Particles through Emulsion Polymerization Using a Cationic Azo Initiator

• Published in: Journal of colloid and interface science Vol. 250; no. 1; pp. 82 - 92
• Main Authors: Luna-Xavier, José-Luiz, Guyot, Alain, Bourgeat-Lami, Elodie
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.06.2002; Elsevier
• Subjects: Applied sciences; cationic initiator; Chemical Sciences; colloidal silica; Composites; emulsion polymerization; Exact sciences and technology; Forms of application and semi-finished materials; heterocoagulation; nanocomposite; Polymer industry, paints, wood; polyoxyethylenic surfactant; Technology of polymers; emulsion polymerization; cationic initiator; nanocomposite; colloidal silica; polyoxyethylenic surfactant; heterocoagulation; Liquid solid adsorption; Non ionic surfactant; Methyl methacrylate polymer; Dispersion reinforced material; Experimental study; Silica; Latex; Composite material; Ethylene oxide polymer; Azo compound; Emulsion polymerization; Nanocomposite; Cationic catalyst; Colloid particle
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.2002.8310

Following a previous work (J. L. Luna-Xavier et al., Colloid Polym. Sci.279, 947 (2001)), silica–poly (methyl methacrylate) (PMMA) nanocomposite latex particles have been synthesized in emulsion polymerization using a cationic initiator, 2,2′-azobis (isobutyramidine) dihydrochloride (AIBA), and a nonionic polyoxyethylenic surfactant (NP30). Silica beads with diameters of 68, 230, and 340 nm, respectively, were used as the seed. Coating of the silica particles with PMMA was taking place in situ during polymerization, resulting in the formation of colloidal nanocomposites with a raspberry-like or a core–shell morphology, depending on the size and nature of the silica beads. The amount of surface polymer was quantified by means of ultracentrifugation and thermogravimetric analysis as extensively described in the first article of the series (see above reference). The influence of some determinant parameters such as the pH of the suspension, the initiator, silica, monomer, or surfactant concentration on the amount of coating polymer and on the efficiency of the coating reaction was investigated in details and discussed in light of the physicochemical properties of the seed mineral. Electrostatic attraction between the positive end groups of the macromolecules and the inorganic surface proved to be the driving force of the polymer assembly on the seed surface at high pH, while polymerization in adsorbed surfactant bilayers (so-called admicellar polymerization) appeared to be the predominant mechanism of coating at lower pH. Optimal conditions have been found to reach high encapsulation efficiencies and to obtain a regular polymer layer around silica.