Electrical Property and Stability of Electrochemically Synthesized Polypyrrole Films Kyung Wha Oh, 1 Hyun Jin Park, 2 Seong Hun Kim 2 1 Department of Home Economics Education, Chung-Ang University, Seoul 156-756, Korea 2 Department of Fiber and Polymer Engineering, Center for Advanced Functional Polymers, Hanyang University, Seoul 133-791, Korea Received 28 April 2003; accepted 12 October 2003 ABSTRACT: Polypyrrole (PPy) films doped with arylsul- fonate dopants were prepared by electrochemical polymer- ization, to investigate the effects of various dopants on con- ductivities, thermal stabilities, and morphologies of PPy films. Also, HCl was added to those dopants as a cooperat- ing dopant, to improve conductivity of PPy films. Conduc- tivity of PPy film doped with the mixture of each dopant and HCl was improved. Temperature dependency on con- ductivity for PPy films doped with various dopants was investigated by heating them from 30 to 300°C. For the film doped with TSA, DBSA, and AQSA, conductivity increased up to 150°C and then rapidly decreased, whereas the con- ductivity of other films decreased after 200°C as temperature increased up to 300°C. Moreover, the film doped with small size dopant such as TSA and HCl/TSA had an intercon- nected porous fibrillar-like morphology. © 2004 Wiley Period- icals, Inc. J Appl Polym Sci 91: 3659 –3666, 2004 Key words: conducting polymers; polypyrrole (PPy); do- pants; electrochemistry; films INTRODUCTION The intrinsic conducting polymers (ICPs) containing -bonded or conjugated polymers have gained great importance with the discovery of doped polyacetylene (PA) in 1977 because of its potential application for electronic materials. 1 According to the results of pre- vious research, electroconductivity of ICPs such as polyacetylene (PA), polyaniline (PANI), polythio- phene (PT), and polypyrrole (PPy) varies with the kind of dopant used because of the differences in oxidation and reduction states. 2 Also, the ICPs al- lowed them to be applied in various electronic de- vices, solid battery electrodes, electrolyte of capacitor, EMI shielding materials, electrochemical ionic sensors, and camouflage sheets in spite of their short history. 3–10 Among the ICPs, PPy has excellent environmental stability, easy synthesis, and higher conductivity than those of other conductive polymers. 5,11,12 Because of its good intrinsic properties, PPy appears promising for use in various fields. However, the application of pyrrole black is limited because it is insoluble and infusible. Electrochemically synthesized PPy film was more useful for application in the field of electronic device because of the direct formation of conducting polymers with control of film thickness and morphol- ogy. In the general electropolymerization, the oxidation of a pyrrole monomer yields a radical cation at the initiation step. It is a pair of radical cations that couple to a dimer and deprotonate, producing a bipyrrole. After the deprotonation step, the bipyrrole is oxidized again and coupled with another oxidized segment. Deprotonation and reoxidation follow, and the pro- cess continues with the formation of oligomeric spe- cies and finally PPy. 13 In general, the conductivity and the thermal stabil- ity of the PPy are strongly dependent on polymeriza- tion conditions such as concentration of pyrrole and dopant, the applied voltage, solvent used, reaction temperature, and kind of dopant. 11,12,14 In a recent investigation of PPy doped with various protonic ac- ids, it was found that HCl and sulfonic acid were the best dopants in terms of conductivity and stability. Because the interchain interaction and the conforma- tion of conducting polymer are varied by change of chemical structure and the charge transfer with do- pants, these also affected the conductivity and the thermal stability. 15,16 Compared with PPy film doped with HCl, the ther- mal stability of the film doped with sulfonic acid was enhanced. 17 However, the conductivity of film doped with sulfonic acid was decreased because of its bulky structure. Moreover, many researchers have reported that the dopant mixtures induced high conductivity. 18 To expand commercial applications for capacitors, re- chargeable batteries and sensors, the conductivity and Correspondence to: S. Kim (kimsh@hanyang.ac.kr). Contract grant sponsor: Korea Research Foundation; con- tract grant number: KRF-2001-042-D00092. Journal of Applied Polymer Science, Vol. 91, 3659 –3666 (2004) © 2004 Wiley Periodicals, Inc.