Kinetic Study of Styrene Atom Transfer Radical Polymerization from Hydroxyl Groups of Graphene Nanoplatelets: Heterogeneities in Chains and Graft Densities Hossein Roghani-Mamaqani, 1 Vahid Haddadi-Asl, 2 Khezrollah Khezri, 3 Mehdi Salami-Kalajahi, 1 Mohammad Najafi 4 1 Department of Polymer Engineering, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran 2 Department of Polymer Engineering and Color Technology, Amirkabir University of Technology, P.O. Box 15875-4413, Tehran, Iran 3 School of Chemistry, University College of Science, University of Tehran, P.O. Box 14155-6455, Tehran, Iran 4 Department of Chemical Engineering, University of Tehran, P.O. Box 14155-6455, Tehran, Iran Confinement effect of graphene nanoplatelets on the kinetics of styrene atom transfer radical polymerization was studied by a “grafting from” reaction. Graphene oxide was modified by different amounts of (3-aminopropyl) trie- thoxysilane and then alpha-bromoisobutyryl bromide from the hydroxyl groups. Polymerization of styrene in the presence of modified graphene and free initiator, ethyl alpha-bromoisobutyrate, was accomplished at 110  C. Then, effect of various graft densities and different gra- phene loadings on the heterogeneous graft and free poly- styrene chains characteristics and also kinetics of polymerization was studied by gas and gel permeation chromatographies. Efficiency of grafting reactions along with the graft contents was studied by X-ray photoelec- tron spectroscopy, elemental analysis, and thermogravi- metric analysis. Confinement effects of graphene on the relaxation behavior of polystyrene chains and also mor- phology of the graphenes were studied by differential scanning calorimetry and transmission electron micros- copy, respectively. POLYM. ENG. SCI., 00:000–000, 2014. V C 2014 Society of Plastics Engineers INTRODUCTION Polymerization techniques based on controlled radical propa- gation are commonly used for synthesis of well-defined poly- mers with predetermined molecular weight and low polydispersity index (PDI) [1]. In these methods, radical propa- gation is mainly controlled by reversible termination reactions, like in nitroxide-mediated polymerization (NMP) [2] and atom transfer radical polymerization (ATRP) [3]. In addition, reversi- ble transfer reactions have been used to control the radical con- centration in the reaction medium, like in reversible addition– fragmentation chain transfer (RAFT) polymerization [4]. Mecha- nistically, methods of reversible termination, more interestingly ATRP, are based on an equilibrium reaction which switches growing chains between active and dormant states. Therefore, irreversible termination reactions are decreased by minimizing the instantaneous concentration of free radicals [5, 6]. Function- ality of the synthesized polymers makes ATRP an interesting tool in synthesis of various graft polymers. Commonly, there are two main routes for the covalent attachment of polymers to a substrate via in situ methods. First, “grafting from” which relies on functionalization of a surface by an initiator and subsequent propagation of polymer chains from the surface [7–14]. And, “grafting through” which is based on the attachment of a double bond containing chemical on the surface and its subsequent incorporation into the polymer chains during the propagation reaction [15–25]. Both of the grafting reactions can result in surface-attached and free polymer chains with different charac- teristics. Studying the effect of confinement and also other mechanistic effects of the substrates on the propagation of poly- mer chains is one of the interesting subjects of polymer chemis- try. Kinetic study of surface grafting reactions not only depends on the substrate, but also grafting reaction and polymerization types are important factors. Kinetics of polymerization can also alter by other factors. Polar mediums and additives with polar functional groups such as phenols, carboxylic acids, and water increase the polymerization rate in an ATRP reaction [20–27]. Therefore, substrates with polar functional groups can result in higher polymerization rates. Review of related literature indi- cates that there are some efforts on the kinetic study of poly- merization in the presence of nanosubstrates [28–37]. In our previous work, we showed that reaction rate of styrene ATRP, molecular weight, and PDI values of the polymer chains increase by adding nanoclay [28]. Chern et al. [29] obtained similar results in the emulsion polymerization of styrene in the presence of montmorillonite (MMT). Liu et al. [30] also observed accelerated polymerization of methyl methacrylate (MMA) in the presence of MMT. Kim et al. [31] reported that using nanoclay in the emulsion polymerization of styrene resulted in a little increase in the molecular weight and a reduc- tion in the PDI of polystyrene chains. Similar results have been obtained by Lee and Jang [32] in the free radical polymerization of MMA in the presence of nanoclay layers in emulsion. In addition, Tong and Deng [33] used modified nanoplatelets of saponite in the miniemulsion polymerization of styrene and observed a reduction in the molecular weight and an increase in the PDI of polystyrene chains. Datta et al. [34] reported the effect of nanoclay and its swelling time in monomer on the kinetics of atom transfer radical polymerization of butylacrylate. Abdollahi and Semsarzadeh [35] also studied the effect of cloi- site 30B on the kinetics of styrene and MMA ATRP. They showed that nanoclay significantly enhances the homopolymeri- zation rate of MMA. Considering “grafting through” reactions, we have studied the effect of nanoclay confinement on styrene Correspondence to: Hossein Roghani-Mamaqani; e-mail: r.mamaghani@sut.ac.ir DOI 10.1002/pen.24010 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2014 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2014