Properties of Covalently Bonded Layered-Silicate/Polystyrene Nanocomposites Synthesized via Atom Transfer Radical Polymerization CHUNG-PING LI, CHING-MAO HUANG, MENG-TING HSIEH, KUNG-HWA WEI Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 30049, Republic of China Received 24 February 2004; accepted 19 September 2004 DOI: 10.1002/pola.20536 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Covalently bonded layered silicated/polystyrene nanocomposites were syn- thesized via atom transfer radical polymerization in the presence of initiator-modified layered silicate. The resulting nanocomposites had an intercalated and partially exfo- liated structure, as confirmed by X-ray diffraction and transmission electron micros- copy. The thermal properties of the nanocomposites improved substantially over those of neat polystyrene. In particular, a maximum increase of 35.5 °C in the degradation temperature was displayed by these nanocomposites. Additionally, the surface elastic modulus and hardness of these nanocomposites were more than double those of pure polystyrene. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 534 –542, 2005 Keywords: polystyrene; clay; atom transfer radical polymerization (ATRP); nano- composites INTRODUCTION Hybrid organic–inorganic nanocomposites have at- tracted substantial interest because of their unique properties, which are otherwise difficult to ob- tain with their individual components. 1,2 Ionically bonded layered-silicate/polymer nanocomposites produced from organically modified silicates are ex- amples. 3–18 In these nanocomposites, montmoril- lonite is typically used as the source of layered sil- icates. Through the replacement of the metal ions in intergalleries of stacked silicates in montmorillon- ite with alkyl or aromatic ammonium ions, interca- lated or exfoliated layered-silicate/polymer nano- composites are produced. These nanocomposites display substantially higher mechanical proper- ties 16 but modest increases in the degradation tem- perature in comparison with pure polymers. On the other hand, if the nanocomposites are formed by covalent bonding between polymers and layered silicates, the interfacial strength between these dis- similar materials becomes stronger and further en- hances their thermal stability and mechanical prop- erties. 18,19 There are several methods for prepar- ing layered-silicate/polymer nanocomposites. The in situ polymerization of the monomer in the pres- ence of a layered silicate is one of the most common ways of achieving a highly efficient dispersion of nanometer-sized layered silicate in a polymer. 20 –22 One particular method of in situ polymerization involves surface grafting via living/controlled radi- cal polymerization. 23–27 One kind of living/con- trolled radical polymerization is atom transfer rad- ical polymerization (ATRP). 28 –36 To control the mo- lecular weight and molecular weight distribution of the polymer chains, we chose the ATRP method to prepare layered-silicate/polymer nanocomposites because it produces a narrower molecular weight Correspondence to: K.-H. Wei (E-mail: khwei@cc.nctu. edu.tw) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, 534 –542 (2005) © 2004 Wiley Periodicals, Inc. 534