Polymer/Laponite Composite Colloids through Emulsion Polymerization: Influence of the Clay Modification Level on Particle Morphology Norma Negrete-Herrera, † Jean-Luc Putaux, ‡ Laurent David, § and Elodie Bourgeat-Lami* ,† Laboratoire de Chimie et Proce ´ de ´ s de Polyme ´ risation, UMR 140 CNRS/ESCPE, Ba ˆ t. 308F, 43 Bd. du 11 NoVembre 1918, BP 2077, 69616 Villeurbanne Cedex, France; Centre de Recherches sur les Macromole ´ cules Ve ´ ge ´ tales, UPR 5301 CNRS, BP 53, F-38041 Grenoble Cedex 9, France; and Laboratoire des Mate ´ riaux Polyme ` res et Biomate ´ riaux, UMR CNRS 5627 IMP, Ba ˆ t. ISTIL, UniVersite ´ Claude Bernard Lyon 1, 69622 Villeurbanne Cedex, France ReceiVed May 10, 2006; ReVised Manuscript ReceiVed September 28, 2006 ABSTRACT: A series of composite latexes have been synthesized by seeded emulsion (co)polymerization of styrene and butyl acrylate in the presence of Laponite clay particles previously functionalized by ion exchange with a free radical initiator: 2,2-azobis(2-methylpropionamidine) hydrochloride (AIBA). Since the AIBA/Laponite intercalation complexes settled down in water immediately after cation exchange, a set of experiments was first carried out in order to establish the conditions required to obtain stable aqueous dispersions of organically modified Laponite. Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) were used to monitor the evolution of particle size and analyze the properties of the aqueous suspensions as a function of the amount of intercalated cation. A series of composite latexes were then prepared by emulsion polymerization using the organoclays as seeds. The composite particles were characterized by cryo-transmission electron microscopy (cryo- TEM), and a particular effort was devoted to analyze the effect of the Laponite modification level on particle morphology. Introduction During the past 10 years, there has been an increased interest in the synthesis of polymer nanocomposites characterized by inorganic particles dispersed into polymeric matrices. 1-5 Since the optical, thermal, rheological, and mechanical properties of these materials strongly depend on the techniques used for their elaboration, a variety of synthetic strategies have been reported worldwide with the aim to control dispersions of the inorganic filler within the host polymer. Among the wide range of nanostructured materials, efforts have focused in recent years on the elaboration of polymer-layered silicate (PLS) nanocom- posites using natural and synthetic clay minerals. 6-9 Again, considerable effort has been made to develop synthetic methods that allow precise control over the composite’s nanostructure. Three main routes are currently reported: exfoliation/adsorption, in-situ intercalative polymerization, and melt intercalation. All three strategies usually require pretreatment of the clay mineral in order to improve its compatibility with the polymer matrix and achieve a good dispersion. This can be realized for instance by treating the clay with silane coupling agents as demonstrated in recent works from our group. 10,11 Organic compounds can also be incorporated into the interlayer galleries through an ion exchange process. Ion exchange reactions with cationic surfac- tants including primary, tertiary, and quaternary ammonium ions render the silicate surface hydrophobic, which makes possible the subsequent intercalation of a variety of monomers and/or polymers. Alternatively, the alkylammonium cations can provide functional reactive groups (e.g., monomers, initiators, catalysts, etc.) that can participate in the polymerization and promote exfoliation of the clay layers. There has been a great number of reports on the synthesis of nanocomposites by in-situ intercalative polymerization. 12-18 However, these approaches mainly produce polymeric solutions of exfoliated clay sheets and do not give rise to particles. Thus, attempts to synthesize PLS latexes through emulsion polymer- ization have been recently described in the open literature. 19-31 This heterophase polymerization process offers many advantages compared to solution or bulk polymerizations such as a low viscosity of the suspension medium, high polymer molecular weights, and the possibility to control particles morphology. In addition, the latex route seems particularly well suited in order to produce homogeneous dispersions of clay minerals into polymer matrices by taking advantage of the swelling behavior of clay platelets in water. Finally, it is worth reminding that emulsion polymers can find applications in a variety of domains including waterborne adhesives, paints, and coating formula- tions. However, to the best of our knowledge, there exist only few reports dealing with the incorporation of ion-exchanged clays into emulsion polymers. In one of these reports, Me- neghetti and Qutubuddin 31 described the synthesis of PMMA- clay nanocomposites via emulsion polymerization at 60 °C using Montmorillonite (MMT) functionalized by either a zwitterionic surfactant (octadecyldimethylbetaine), a cationic surfactant (benzalkonium chloride), or an anionic surfactant (sodium dodecyl sulfate) through ion exchange. They showed that the nanoparticles morphology and the latex properties were both affected by the nature of the interaction between the surfactant and the clay surface. In a related work, Choi et al. 19 reported the synthesis of PMMA/Na-MMT nanocomposites through emulsion polymerization of methyl methacrylate (MMA) using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) or so- † UMR 140 CNRS/ESCPE. ‡ UPR 5301 CNRS. § UMR CNRS 5627 IMP. * Corresponding author: e-mail bourgeat@lcpp.cpe.fr, Tel 33 (0)4 72 43 17 77; Fax 33 (0)4 72 43 17 68. 9177 Macromolecules 2006, 39, 9177-9184 10.1021/ma0610515 CCC: $33.50 © 2006 American Chemical Society Published on Web 11/23/2006