Polymer Communication Enhanced electrical conductivity of polypyrrole prepared by chemical oxidative polymerization: effect of the preparation technique and polymer additive H.C. Kang, K.E. Geckeler * Laboratory of Applied Macromolecular Chemistry, Department of Materials Science and Engineering, Kwangju Institute of Science and Technology, 1 Oryong-dong, Puk-gu, Kwangju 500-712, South Korea Received 15 November 1999; received in revised form 6 January 2000; accepted 8 February 2000 Abstract The electrical conductivity of chemically prepared polypyrrole in aqueous solution was found to be strongly dependent on the preparation technique and polymer additive. Owing to the hygroscopic nature of polypyrrole, it is essential to remove residual water. Accordingly, the conductivity can be enhanced by about two orders of magnitude when using a preparation technique that includes a washing treatment with organic solvents and drying under vacuum at elevated temperatures to attain maximum removal of water. Thus, the electrical conductivity of polypyrrole is affected not only by reported factors such as the ratio of oxidant to pyrrole, reaction temperature, and reaction time, but also by the preparation technique. Additionally, a significant enhancement of the conductivity up to 90 S cm -1 by using of poly(ethylene glycol) as an additive during the polymerization could be achieved.  2000 Published by Elsevier Science Ltd. All rights reserved. Keywords: Additive; Polypyrrole; Electrical conductivity 1. Introduction Although polypyrrole (PPY) has been prepared by electro- chemical polymerization, the alternative approach of chemi- cal oxidative polymerization has been also pursued, because it allows mass production within a short time. Chemical preparation of PPYs by using various conditions (change of solvent, oxidant, dopant, ratio of oxidant to pyrrole, reac- tion temperature, reaction time, etc.) has been reported in the literature [1,2]. Especially in the aqueous system, PPY showed a high conductivity when the ratio of ferric chloride to pyrrole was reduced, however, the yield was then also decreased. In addition, the reaction temperature has to be low (0–5°C) to obtain good conductivities, if the ferric salt is used. Recent studies also showed that the addition of polymers can influence the conductivity by sterical stabilization of the polypyrrole chains [1]. To this end, water-soluble polymers of molecular masses over 20,000 g mol -1 such as methyl cellulose, poly(vinyl alcohol-co-acetate), poly(ethylene oxide), poly(vinylpyrrolidone), poly(2-vinylpyridine), poly (vinylmethylether), and others, were studied. When using these additives, conductivities of a broad range 1 × 10 -9 –12 S cm -1  have been obtained [1]. Specifically, for poly(ethylene oxide) with a molar mass of 130,000 g mol -1 a conductivity of 2 × 10 -3 S cm -1 was found [3]. Further, low-molecular surfactants such as sodium dodecylbenzene sulfonate, sodium alkylnaphthalene sulfonate, and sodium alkylsulfonate were investigated [4–6]. The influence of air and oxygen-free atmosphere has been also studied recently for the application of polypyrrole as a solid electrolyte for capacitors [7]. In this investigation, covalently bonded oxygen was detected by FT-IR spectro- scopy. Interestingly, no difference in the thermostability of oxidized and native PPY was found. In line with these studies, the thermal stability of the electrical conductivity was also found to be enhanced by using an antioxidative dopant [8]. Thus, the conductive stability was increased by aromatic sulfonates such as 2-hydroxy-5-sulfobenzoic acid up to 150°C in air. The pronounced effect is explained and confirmed by IR spectroscopy with deuterized PPY by a thermal stabilization mechanism involving the suppression of proton dissociation from the 1-position and maintaining the conjugated structure by supplying protons from the dopant. Very recently, other approaches, e.g. the use of binary Polymer 41 (2000) 6931–6934 0032-3861/00/$ - see front matter  2000 Published by Elsevier Science Ltd. All rights reserved. PII: S0032-3861(00)00116-6 * Corresponding author. Tel.: + 82-62-970-2316; fax: + 82-62-970- 2338. E-mail address: keg@kjist.ac.kr (K.E. Geckeler).