Chemical Engineering Journal 181–182 (2012) 770–778 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal jo u r n al hom epage: www.elsevier.com/locate/cej Synthesis of exfoliated poly(styrene-co-methyl methacrylate)/montmorillonite nanocomposite using ultrasound assisted in situ emulsion copolymerization B.A. Bhanvase a , D.V. Pinjari b , P.R. Gogate b , S.H. Sonawane a,c , A.B. Pandit b,∗ a Vishwakarma Institute of Technology, 666 Upper Indira Nagar, Pune-411 037, India b Institute of Chemical Technology, N.P. Marg, Matunga, Mumbai-400 019, India c University Department of Chemical Technology, North Maharashtra University, Jalgaon-425001, India a r t i c l e i n f o Article history: Received 14 June 2011 Received in revised form 15 November 2011 Accepted 22 November 2011 Keywords: Ultrasound P(MMA-co-St)/O-MMT composite Emulsion copolymerization Nanocomposites Thermal stability a b s t r a c t The present work deals with the synthesis of poly(methyl methacrylate-co-styrene)/montmorillonite [P(MMA-co-St)/O-MMT] nanocomposite using ultrasound assisted emulsion copolymerization operated in a semibatch manner. The synthesis process is based on dispersing montmorillonite (MMT) clay in the monomer (styrene) and surfactant (sodium dodecyl sulfate) under the influence of ultrasonic irradiations. Investigations have been carried out using treated MMT clay by quaternary ammonium salt (octadecy- lamine) as a starting material for establishing the dependency on the stability of emulsion and formation of latex. X-ray diffractrogram (XRD) have clearly established the complete exfoliation of MMT clay into the polymer. The exfoliated structure of nanocomposites has also been confirmed by transmission electron microscopy (TEM). It has been observed that both polymerization rate (R P ) and the fractional conver- sion decreased with an increase in the O-MMT clay loading in the emulsion polymerization system. The zeta potential and particle size analysis showed that nanocomposite latexes were electrostatically stable and average particle size was in the range of 156.58 to 191.23 nm with narrow particle size distribution. It has been observed that the exfoliated P(MMA-co-St)/O-MMT nanocomposite exhibits a higher glass transition temperature (T g = 152.7 ◦ C) and lower heat of reaction (H = −265 J/g) at 1% O-MMT loading as compared to the neat copolymer (T g = 127.3 ◦ C, H = −437.5 J/g). Nanocomposite formed using current method have been shown to give better thermal stability attributed to the interaction of O-MMT platelets with polymer leading to cross-linking enhancement. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In the research area of material science, polymer/layered nanocomposite synthesis is one of the emerging areas due to the wide range of applications exhibited by the layered nanocompos- ites based on their versatile properties based on the combination of starting materials and the synthesis approach [1–6]. Two nanocomposites with dissimilar microstructures, namely exfoli- ated and intercalated could exist together when clay materials are dispersed into the polymer matrix [2]. In the intercalated com- posites, gallery spacing of layered silicate is increased by using a long chain organic molecule, which allows the occupation of the polymer chains into gallery spacing. In order to synthesize exfoli- ated nanocomposite structure, high mechanical shear is required to disperse the clay platelets into the host matrix [5]. Interca- lated nanocomposite microstructure are suitable for development of barrier resistance nanocomposite application [4]. Exfoliated ∗ Corresponding author. Tel.: +91 22 33612012; fax: +91 22 33611020. E-mail address: ab.pandit@ictmumbai.edu.in (A.B. Pandit). polymer clay hybrid structures offer superior mechanical and ther- mal properties, because of the homogeneous dispersion of clay in the polymer matrix, as well as a large interfacial area of clay layers interacting with the interspaced polymer layers [7]. Poly(methyl methacrylate) (PMMA) has excellent transparency and high modulus, but its melt viscosity is on a significantly higher side (>10 4 Pa s). It is also reported that mechanical properties of PMMA such as abrasion and wear are relatively low and indepen- dent of molecular weight. On the other side, polystyrene (PS) has relatively low modulus [8] and high abrasion resistance, load bear- ing capacity and greater tensile strength [9]. Thus the formation of a copolymer using these two polymers can compensate their demerits and the resulting composite material can have signifi- cant range of applications. The addition of clay to the polymer matrix can be further helpful in deciding the properties of the poly- mer matrix. Several methods such as melt mixing method [10], bulk polymerization [2,11–14], solution polymerization and emul- sion polymerization [15–20] have been employed to synthesize copolymer/clay nanocomposite. Out of these techniques, emul- sion polymerization has the important advantage of generating monodispersed polymer nanoparticles with controlled molecular 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.11.084