Vinylester Resin-Clay Hybrids Using Various Intercalating Agents Tarek Agag, 1 * Ahmed Akelah, 1 Mohamed Abdelwahab, 1 Tsutomu Takeichi, 2 Hiroyuki Muto 2 1 Polymer research group, Chemistry Department, Faculty of Science, Tanta University, Tanta 31527, Egypt 2 School of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580, Japan Received 23 March 2008; accepted 5 August 2009 DOI 10.1002/app.31293 Published online 7 October 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Vinylester resin-clay hybrids were prepared by the mixing different types of organically-modified montmorillonite (OMMT) with vinylester resin (VER) pre- polymer, followed by thermal polymerization. VER pre- polymer was synthesized from the reaction of diglycidylether of bisphenol-A (DGEBA) with acrylic acid. Various types of organic ammonium salts have been used as intercalating agents for montmorillonite, including N,N- dimethyl-N-(4-vinylbenzyl)stearyl ammonium chloride (VSA), N-allyl-N,N-dimethyl-stearyl ammonium chloride (ASA) and N,N-dimethyl-stearyl ammonium chloride (SA). The dispersion of OMMT into VER matrix was studied by XRD, which indicates the dependence of the morphology mainly on the OMMT content. UV–vis spectra of the hybrids were used to give a quantitative value of the effect of OMMT content on the transparency of VER/OMMT hybrid films. Also, the Vickers test has been performed to study the effect of OMMT content on the surface hardness of the hybrid films. In addition, the thermal properties of the hybrids have been characterized by measuring the softening points and thermogravimetric analyses of the hybrids in comparison with the pure resin. V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2060–2068, 2010 Key words: vinylester resin; montmorillonite; intercalating agent; nanocomposites; hardness; softening point INTRODUCTION Polymer nanocomposites are attractive, because they often show an improvement in mechanical, thermal, barrier, and optical properties, as well as fire retard- ancy. 1,2 The use of layered silicate clays as precur- sors to prepare organic-inorganic nanocomposites has been extensively studied with various types of polymers. 3,4 The most commonly used clay type for preparation of nanocomposites is montmorillonite (MMT), which is an aluminosilicate mineral. The lat- tice structure of MMT consists of layers organized in stacks with periodic interlayers space. The thickness of each layer is  0.96 nm. The interlayer, referred to as gallery, is normally 0.3–0.5-nm thick. Because of the hydrophilic nature of MMT, the diffusion of nonpolar polymer into the clay galleries is not possi- ble. The best approach to increase the compatibility of MMT with nonpolar polymers is surface modifi- cation of MMT to produce a hydrophobic environ- ment within the galleries of the organically modified MMT. This modification process is achieved by an ion-exchange reaction of the inter-gallery inorganic cations with long chain organic cations to make the interlayer galleries hydrophobic in nature. Most clay modifications have been carried out by using or- ganic ammonium salts. In addition, the organic am- monium cations can provide functional groups that react with the monomer or polymer to improve the interfacial strength between organoclay as a reinforc- ing agent and polymer matrix. 5,6 Polymer-clay nanocomposites can be prepared by the dispersion of organically modified MMT (OMMT) into the monomers or prepolymers with or without the presence of solvent followed by poly- merization. A variety of polymer clay nanocompo- sites have been synthesized and studied using thermoplastic, thermoset and elastomeric polymers. Some examples of thermoplastic polymers include nylon 6 7,8 and styrene. 9 Examples of thermosets are epoxy, 10–13 benzoxazine resin 14 and phenolic resin, 15 and for elastomers are amine-terminated butadiene nitrile (ATBN), 16 silicon rubber, 17 and polyurethane. 18 Vinylester resin (VER) attracted much attention due to its easy of preparation and attractive proper- ties. 19 The nature of VER backbone structure offers toughness and flexibility to the cured resin as well as chemical resistance. 20 Also, the presence of sec- ondary hydroxyl groups impairs polarity which improves its adhesion and wetting properties. *Present address: Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7202, USA. Correspondence to: T. Agag (taa16@case.edu) and A. Akelah (ahmed_akelah@hotmail.com). Journal of Applied Polymer Science, Vol. 115, 2060–2068 (2010) V C 2009 Wiley Periodicals, Inc.