UNCORRECTED PROOF Polymer Communication Mechanical properties of intercalated cyanate ester – layered silicate nanocomposites Sabyasachi Ganguli a , Derrick Dean a, * , Kelvin Jordan b , Gary Price c , Richard Vaia d a Center for Advanced Materials, Tuskegee University, 101 Chappie James Center, Tuskegee, AL 36088, USA b Raytheon Electronic Systems, Tuscan, AZ, USA c University of Dayton Research Institute, Dayton, OH, USA d Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, OH, USA Received 24 June 2002; received in revised form 23 September 2002; accepted 26 September 2002 Abstract Cyanate ester resins are among the most important engineering thermosetting polymers and have received attention because of their outstanding physical properties such as low water absorptivity and low outgassing. However, like most thermosets their main drawback is brittleness. Nanocomposites of cyanate esters were prepared by dispersing organically modified layered silicates (OLS) into the resin. Inclusion of only 2.5% by weight of OLS led to a marked improvement in physical and thermal properties (Coefficient of thermal expansion, T g and effective thermal stability). Most impressively, a 30% increase in both the modulus and toughness was obtained. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Cyanate esters; Nanocomposites; High temperature thermosets 1. Introduction Cyanate esters are currently finding widespread use in high performance electronic and aerospace applications because of their high thermal stability, low outgassing, and radiation resistance [1]. These properties are accompanied by low dielectric (2.5 – 3.1), dimensional stability at solder temperatures (T g : 250 – 290 8C) and low moisture absorption (0.6 – 2.5%). Cyanate ester homopolymers absorb less water at saturation than epoxy, bismaleimide (BMI), and poly- imide resins. Unfortunately, highly cross-linked thermosets, such as cyanate esters, tend to be brittle and to have reduced impact resistance. Although a cured cyanate resin has a relatively higher toughness than a cured BMI or a cross- linked epoxy resin, it still requires suitable modification to improve toughness without reducing the intrinsic physical strength for structural applications. To improve the toughness of a cured cyanate resin, approaches such as the preparation of flexibilized cyanate resins, the incorporation of monocyanates, the utilization of rubber toughening technologies, and the preparation of semi-interpenetrating networks (SIPNs) have proven useful [2]. However, toughening usually occurs at the expense of other characteristics of the cyanate ester resin. Note that a few examples of utilization of thermoplastic modifiers to improve mechanical properties without sacrificing tough- ness do exist, such as Pearson and Yee’s investigations of DGEBA epoxies [3], but attempts to provide a broad understanding to enable generalization to various thermoset systems have been unsuccessful. Interest in the addition of nanoscale fillers, such as layered silicates and clays, to polymers as an approach to enhance performance has substantially increased recently [4]. Polymer – clay nanocomposites were first reported in the literature as early as 1961, when Blumstein demonstrated polymerization of vinyl monomers intercalated into mont- morillonite clay [5]. Numerous methods to prepare poly- mer – clay nanocomposites have recently been developed by several groups [6–8]. For example, Pinnavai et al. have achieved exfoliated morphologies using epoxy resins [6]. This is presumably due primarily to the relatively high polarity of these systems, which promotes diffusion into the clay galleries. The acidity of the alkylammonium ions is thought to catalyze homopolymerization of DGEBA epoxy resins. The maximum layer expansion is obtained when 0032-3861/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(02)00709-7 Polymer 44 (2003) 1315–1319 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 1-334-727-4247; fax: þ1-334-727-4224. E-mail address: deand@tusk.edu (D. Dean).