Kinetics of the emulsion copolymerization of MMA/BA in the presence of sodium montmorillonite A. Bonnefond, M. Paulis, J.R. Leiza ⁎ Institute for Polymer Materials, POLYMAT, Dpto. de Química Aplicada, Facultad de Ciencias Químicas, University of the Basque Country, Joxe Mari Korta zentroa, Tolosa Etorbidea 72, 20018 Donostia-San Sebastián, Spain abstract article info Article history: Received 18 June 2010 Received in revised form 9 November 2010 Accepted 11 November 2010 Available online 21 November 2010 Keywords: Sodium montmorillonite Kinetics of emulsion polymerization Polymer particle nucleation The kinetics of the emulsion copolymerization of methyl methacrylate/butyl acrylate (MMA/BA = 50/50) in the presence of sodium montmorillonite (Na-MMT) was investigated. Sodium laurylsulfate was used as surfactant at different concentrations and potassium persulfate as initiator. Two series of experiments were carried out at 30% and 10% solids content and varying the amount of surfactant and sodium montmorillonite. The effect of surfactant and sodium montmorillonite content on the stability of the final latices was assessed. The effect on particle nucleation, polymerization kinetics and molar mass distribution was also discussed, and compared with the predictions of the Smith–Ewart theory. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The research on polymer/clay nanocomposites has significantly grown during the last two decades. The increase of researchers' interest came from the enhanced properties of polymer/clay mineral nanocomposites. In comparison to traditional microcomposites, polymer/clay mineral nanocomposites present improved mechanical (strength and stiffness) and thermal properties, reduced gas, water and hydrocarbon permeability, and higher fire resistance (Diaconu et al., 2008a; Lee and Jang, 1996; Okamoto, 2004; Pan et al., 2004). In-situ polymerization in the presence of clay mineral particles is the most appropriate route to produce exfoliated polymer/clay mineral nanocomposites. Among the in-situ polymerization methods, emulsion polymerization is most used to produce waterborne polymer/clay mineral nanocomposites (Paulis and Leiza, 2009). Many authors took advantage of this technique to exfoliate the clay mineral particles in the final nanocomposites. Thus, Zhang and Wilkie (2004) prepared PS nanocomposites by emulsion and bulk polymer- ization, and clay mineral exfoliation was only obtained by means of emulsion polymerization. Bandyopadhyay et al. (2000) first synthe- sized waterborne PMMA with exfoliated montmorillonite by emul- sion polymerization. Later on PBA-co-PMMA/MMT nanocomposites with exfoliated clay mineral morphology was synthesized by emulsion polymerization (Choi and Chung, 2003). The success of producing exfoliated nanocomposites by means of in-situ emulsion polymerization is likely based on the delamination of sodium smectites in water (Norrish, 1954). Thus, at montmorillonite contents lower than 1.5% in water, the montmorillonite particles were delaminated as no reflection was observed on SAXS (Diaconu et al., 2008a). Few contributions dealt with the study of the kinetics of polymerization in the presence of exfoliated clay mineral particles in the water phase. Furthermore, detailed studies of the influence of the clay mineral on the stability of latices are scarce. Solomon (1968) and Solomon and Loft (1968) studied the spontaneous polymerization of different monomers in the presence of montmorillonite and kaolinite. Even if the bulk polymerization of some monomers (styrene, S and hydroxyethyl methacrylate, HEMA), was favoured in the presence of the clay minerals, the polymerization of methyl methacrylate, MMA, was inhibited by the clay. The authors attributed the inhibition to the electron acceptor character of the aluminium ions at the clay mineral edges. Talapatra et al. (1985) studied the aqueous phase polymerization of MMA in the presence of montmorillonite and hydrogen bentonite and Bhattacharya et al. (1989) in the presence of montmorillonite. Hydrogen bentonite alone did not induce the polymerization of MMA, but the addition of ethanol to MMA/bentonite favoured the polymerization. On the other hand, thiourea was needed to polymerize MMA in the presence of montmorillonite. The authors attributed the activation to electron transfer from thiourea or ethanol to Fe 3+ ions in the montmorillonite creating radicals that could activate the polymerization. In these cases, the inhibiting effect of the aluminium ions at the edges was deactivated by the presence of water molecules. Esaimi (1997) did also consider the polymerization of MMA in the presence of clay mineral and water, but in this case potassium persulfate (KPS) was also added as initiator. The presence of montmorillonite increased the MMA polymerization rate at different temperatures, which was Applied Clay Science 51 (2011) 110–116 ⁎ Corresponding author. Tel.: +34 943 015329; fax: +34 943 01 7065. E-mail address: jrleiza@ehu.es (J.R. Leiza). 0169-1317/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2010.11.011 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay