pubs.acs.org/Macromolecules Published on Web 06/17/2009 r 2009 American Chemical Society Macromolecules 2009, 42, 4511–4519 4511 DOI: 10.1021/ma9001897 One-Step Synthetic Route for Conducting Core-Shell Poly(styrene/pyrrole) Nanoparticles Jung Min Lee, Dong Gyu Lee, Sun Jong Lee, and Jung Hyun Kim* Department of Chemical and Biomolecular Engineering, Yonsei University, 134 Shinchon-Dong, Seodaemoon-Gu, Seoul 120-749, Republic of Korea In Woo Cheong* Department of Applied Chemistry, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu 702-701, Republic of Korea Received January 28, 2009; Revised Manuscript Received May 22, 2009 ABSTRACT: Conducting core-shell poly(styrene/pyrrole) (poly(St/Py)) particles were successfully pre- pared by a one-step solution route in soap-free emulsion polymerization. Hydrogen peroxide (H 2 O 2 ) and a trace of ferric chloride (FeCl 3 ) were used as an initiator couple to carry out Fe 3+ -catalyzed oxidative polymerization. The average particle size of the particle was approximately 250 nm and its core-shell morphology (shell thickness ∼20-30 nm) was proved with transmission electron microscopy. The SEM images after CHCl 3 dissolution supported a clear evidence of distinct core-shell morphology, and which was confirmed by DSC and TGA analyses. We proposed a growth mechanism for the formation of the core-shell poly(St/Py) particles based on the time-evolution morphology of the particle. The result was also corrobo- rated by the time-evolution GPC, FT-IR and ζ-potential data. The surface compositions of the particles were examined by X-ray photoelectron spectroscopy (XPS). The doped particles showed a high conductivity in the dry state. Introduction Poly(pyrrole) (PPy) is not only an important component of conjugated polymers due to its usability in a wide range of applications, but also one of the most studied conducting poly- mers because it has a higher conductivity and better environ- mental stability in the conductive (oxidative) state than any other conducting polymers. PPy can be easily prepared by chemical oxidative 1 and electrochemical polymerization. 2 In a chemical oxidative polymerization, (NH 4 ) 2 S 2 O 8 ,H 2 O 2 , and many kinds of salts containing transition metal ions, e.g., FeCl 3 or CuCl 2 , are generally used as oxidants. Particularly in the case of conven- tional chemical oxidative polymerization using FeCl 3 as an oxidant, a very large molar concentration of FeCl 3 (e.g., FeCl 3 : pyrrole=2.5:1) is often required to oxidize pyrrole monomers. 3 In addition, it should be removed from the final product to obtain the original electrical conductivity of the PPy; consequently, washing procedures such as washing after centrifugation, 4 dia- lysis 5 or extraction method with ethylenediaminetetraacetic acid (EDTA) solution are needed. 6 In this current work, however, only a trace amount of FeCl 3 was required to polymerize pyrrole monomers. Therefore, it is not necessary to remove FeCl 3 in the Fe 3+ -catalyzed oxidative polymerization because only a catalytic amount of FeCl 3 was used. 7 For the wide range application of PPy in various fields, it is important to improve its processability, conductivity, and envir- onmental stability. Many researchers have focused on improving the processability of conducting polymers. 8-13 Often the solu- bilization of conductive polymers can be achieved through functionalization of the starting materials with a suitable side chain prior to polymerization. 14-16 These substituted PPys; however, possess a lower conductivity than the pristine PPys. Recently many other methods have been investigated in the preparation of soluble or swollen PPy 17-21 and dispersible fine powdered PPy 22-26 to improve their poor processability. For example, sterically stabilized PPy colloids can be easily synthe- sized in an aqueous media by chemically polymerizing pyrrole monomers in the presence of a suitable water-soluble polymer, such as methyl cellulose or poly(vinyl alcohol) 23,27 An alternate route for the preparation of colloidal conducting polymers involves coated particles with a thin layer of conjugated polymer to form conducting composites with a core-shell structure. 28-31 There have been numerous efforts to synthesize core-shell colloid materials with tailored structural, optical and surface properties, which are applicable to various fields, i.e., coatings, electronics, catalysis, separations, and diagnostics. 32-34 Its popu- larity is due to the expected improvement of polymer processa- bility and the unique intrinsic properties in dispersed nanometer or micrometer-sized materials. If the conducting polymer shell- layer is continuous, it can lead to a relatively high conductivity in spite of the low conducting polymer loading. Yassar et al. reported that sulfonic and carboxylic acid coated poly(styrene) could be coated with PPy overlayer using FeCl 3 . 25 To the best of our knowledge, one-step solution route for the preparation of core-shell conducting polymer particles, i.e., poly(styrene/pyrrole) (poly(St/Py)), has never been reported. Usually, the core-shell conjugated polymer particles were pre- pared by multistep procedures using seed particles as a core material. 28-31,35,36 These techniques, however, have significant limitations of being both expensive and time-consuming due to the multistep procedures. Here, we proposed a facile method of *Corresponding authors. (J.H.K.) Telephone: +82 2 2123 7633. Fax: +82 2 312 0305. E-mail: jayhkim@yonsei.ac.kr. (I.W.C.) Telephone: +82 53 950 7590. Fax: +82 53 950 6594. E-mail: inwoo@knu.ac.kr.