Synthesis and structural study of polypyrroles prepared in the presence of surfactants Ma ´ria Omastova ´ a,* , Miroslava Trchova ´ b , Jana Kova ´r ˇova ´ c , Jaroslav Stejskal c a Polymer Institute, Slovak Academy of Sciences, Du ´bravska ´ cesta 9, 842 36 Bratislava, Slovak Republic b Faculty of Mathematics and Physics, Charles University Prague,180 00 Prague 8, Czech Republic c Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic Received 10 June 2002; accepted 14 October 2002 Abstract Conducting and stable polypyrrole (PPy) was synthesized by chemical oxidative polymerization of pyrrole in aqueous solution containing an oxidant, ferric sulfate, and a surfactant. Anionic surfactants: sodium dodecylbenzenesulfonate, dodecylbenzenesulfonic acid, sodium dodecyl sulfate, poly(ethylene oxide)-n-alkyl-3-sulfopropyl ether potassium salt; cationic surfactant: tetradecyltrimethylammonium bromide; and non-ionic surfactants: poly(ethylene oxide) (10) iso-octylphenyl ether (Triton 1 X-100), poly(ethylene oxide) (20) sorbitan monolaurate (Tween 1 20) and poly(ethylene oxide) (20) sorbitan monostearate (Tween 1 60) were used as additives. Results of the elemental analysis and FTIR spectroscopy proved that only the anionic surfactants were incorporated into PPy similarly as the doping anion. This leads to a better stability towards the deprotonation. Also thermal stability, checked by TGA in air, was improved. Scanning electron microscopy studies showed that the presence of the anionic surfactant strongly influenced the morphology of the polymer product. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Chemical polymerization; Conducting polymer; FTIR spectroscopy; Polypyrrole; Stability; Surfactants; TGA 1. Introduction Polypyrrole (PPy) is one of the most studied conducting polymers because of its good electrical conductivity, envir- onmental stability and relative ease of synthesis. PPy can be prepared by electrochemical [1–3] or chemical [4,5] oxida- tion of pyrrole in various organic solvents and in aqueous media. In a chemical oxidative polymerization of pyrrole monomer many oxidants have been used, ferric chloride [4,6], ferric perchlorate [7], ammonium peroxydisulfate [8,9], and others. The preparation conditions and various additives introduced into reaction mixture influence the properties of final conducting polymer [10,11]. Colloidally stable PPy particles were prepared using polymeric stabilizers and surfactants [12–14]. The formation process of PPy films on electrode surfaces was studied during the electro- polymerization of pyrrole in the presence of sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (DBSNa) [15–17]. The pyrrole monomer is considered to be preferen- tially dissolved into the micellar assembly because of its hydrophobic nature. From monomer–micelle bilayers the nucleation of the PPy/DBS  grain is considered to start at the defect of bilayer adsorbed on the electrode surface. An electrochemical sensor for the detection of non-electroactive cations (Li þ , Na þ and K þ ) based on the incorporation of dodecyl sulfate anion into PPy by electropolymerization was prepared [18]. The authors have proposed the application of this electrode as a sensor in flow-injection analysis and in high-performance ion chromatography. Dodecyl-sulfate- doped PPy was synthetized electrochemically by anodic polymerization of pyrrole in the presence of SDS in aqueous solution and used as a surfactant sensor [19]. The electrode made of poly(vinyl chloride) membrane, plasticized with 2- nitrophenyl octyl ether and containing PPy and SDS, was prepared. The electrode was highly selective to dodecyl sulfate anion over diverse inorganic anions. The effect of non-ionic surfactant additives such as poly(ethylene oxide) (n) nonyl phenyl ether (n ¼ 4, 7, 10, 15 and 21), poly(ethy- lene oxide) (n) octadecyl ether (n ¼ 10 and 20) on the electropolymerization of pyrrole in aqueous medium was studied [20]. The mechanical properties and surface smooth- ness of PPy films prepared from the aqueous solutions with addition of the non-ionic surfactants were greatly improved in Synthetic Metals 138 (2003) 447–455 * Corresponding author. Fax: þ421-2-5477-5923. E-mail address: upolmaom@savba.sk (M. Omastova ´). 0379-6779/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0379-6779(02)00498-8