Enzymatically Synthesized Conducting Polyaniline Wei Liu, Jayant Kumar, Sukant Tripathy, Kris J. Senecal, ² and Lynne Samuelson* ,² Contribution from the Center for AdVanced Materials, Departments of Chemistry and Physics, UniVersity of Massachusetts Lowell, Lowell, Massachusetts 01854, and Materials Science Team, U.S. Army Soldier & Biological Chemical Command, Natick, Massachusetts 01760 ReceiVed June 29, 1998 Abstract: A novel strategy for the enzymatic synthesis of a water-soluble, conducting polyaniline (PANI)/ sulfonated polystyrene (SPS) complex is presented. The enzyme horseradish peroxidase (HRP) is used to polymerize aniline in the presence of a polyanionic template, sulfonated polystyrene. The synthesis is simple, and the conditions are mild in that the polymerization may be carried out in a 4.3 pH buffered aqueous solution, with a stoichiometric amount of hydrogen peroxide and a catalytic amount of enzyme. UV-visible absorption, FTIR, GPC, elemental analysis, and conductivity measurements all confirm that the electroactive form of PANI, similar to that which is traditionally chemically synthesized, is formed and complexed to the SPS. The reversible redox activity of the polyaniline displays a unique hysteresis loop with pH change. Cyclic voltammetry studies show only one set of redox peaks over the potential range of -0.2 to 1.2V, which suggests that the PANI/SPS complex is oxidatively more stable. The conductivity of the complex is found to increase with the molar ratio of PANI to SPS. Conductivities of 0.005 S/cm are obtained with the pure complex and may be increased to 0.15 S/cm after additional doping by exposure to HCl vapor. This enzymatic approach offers unsurpassed ease of synthesis, processability, stability (electrical and chemical), and environmental compatibility. Introduction In recent years there has been a tremendous interest in the use of conducting polymers in electronics applications because of their wide range of electrical, electrochemical, and optical properties as well as their good stability. 1-3 In particular, polyaniline (PANI) has been investigated for such applications as organic lightweight batteries, 4 microelectronics, 5 optical displays, 6 antistatic coatings, and electromagnetic shielding materials. 7 PANI is commonly synthesized by oxidizing aniline monomer either electrochemically or chemically. 8,9 The final electroactive polymer can exist in various oxidation states, which are characterized by the ratio of amine to imine nitrogen atoms. 10 PANI can be doped either by protonation with a protonic acid or by charge-transfer with an oxidation agent, 11 and the electronic and optical properties may be controlled reversibly by varying the doping level. 11b, 12 For practical applications, a conducting polymer must be cost- effective to synthesize and purify, have good chemical and electrical stability, and be able to be easily processed from either solution or the melt. 13 PANI, although one of the most promising conducting polymers from the standpoint of application, has nevertheless found only limited commercial application due to harsh or limited chemical synthetic procedures and poor solubility in common solvents. Many attempts have been made to improve the processability of PANI including modification of the polymer with various ring or N-substitutes, 14-17 post- * To whom correspondence should be addressed. ² U.S. Army Soldier & Biological Chemical Command. (1) (a) MacDiarmid, A. G. Synth. Met. 1997, 84, 27. (b) MacDiarmid, A. G.; Chiang, J. C.; Richter, A. F.; Epstein, A. J. Synth. Met. 1987, 18, 285. (c) Chinn, D.; Dubow, J.; Liess, M.; Josowicz, M.; Janata, J. Chem. Mater. 1995, 7, 1504. (d) MacDiarmid, A. G.; Epstein, A. J. In Science and Applications of Conducting Polymers; Salaneck, W. R., Clark, D. T., Samuelsen, E. J., Eds.; Adam Hilger: Bristol, England, 1990. (e) Cao, Y.; Li, S.; Xue, Z.; Guo, D. Synth. Met. 1986, 16, 305. (2) (a) Dong, Y.; Mu, S. Electrochim. Acta 1991, 36, 2015. (b) Noufi, R.; Nozik, A. J.; White, J.; Warren, L. F. J. Electrochem. Soc. 1982, 129, 2261. (3) (a) Chen, W.-C.; Jenekhe, S. A. Macromolecules 1992, 25, 5919. (b) Westerweele, W.; Smith, P.; Heeger, A. J. AdV. Mater. 1995, 7, 788. (4) (a) Genies, E. M.; Hany, P.; Santier, C. J. J. Appl. Electrochem. 1988, 18, 285. (b) Kaneko, M.; Nakamura, H. J. Chem. Soc., Chem. Commun. 1985, 346. (5) (a) Paul, E. W.; Rico, A. J.; Wrighton, M. S. J. Phys. Chem. 1985, 89, 1441. (b) Huang, W. S.; Lecorre, M. A.; Tissier, M. J. Vac. Sci. Technol. 1991, B9, 3428. (c) Chen, S.-A.; Fang, Y. Synth. Met. 1993, 60, 215. (6) (a) Kitani, A.; Yano, J.; Sasaki, K. J. Electroanal. Chem. 1986, 209, 227. (b)Jelle, B. P.; Hagen, G. J. Electrochem. Soc. 1993, 140, 3560. (7) (a) Wood, A. S. Mod. Plast. 1991, August, 47. (b) Epstein, A. J.; Yue, J. U.S. Patent 5,237,991, 1991. (8) (a) Diaz, A. F.; Logan, J. A. J. Electroanal. Chem. 1980, 111, 111. (b) Watanabe, A.; Mori, K.; Iwabuchi, A.; Iwasaki, Y.; Nakamura, Y.; Ito, O. Macromolecules 1989, 22, 3521. (c) Verghese, M. M.; Ramanathan, K.; Ashraf, S. M.; Kamalasanan, M. N.; Malhotra, B. D. Chem. Mater. 1996, 8, 822. (9) (a) Focke, W. W.; Wnek, G. E.; Wei, Y. J. Phys. Chem. 1987, 91, 5813. (b) Wu, C.-G.; Chen, J.-Y. Chem. Mater. 1997, 9, 399. (c) Liu, G.; Freund, M. S. Macromolecules 1997, 30, 5660. (10) (a) Masters, J. G.; Sun, Y.; MacDiarmid, A. G.; Epstein, A. J. Synth. Met. 1991, 41, 715. (b)D’Aprano, G.; Leclerc, M.; Zotti, G. Macromolecules 1992, 25, 2145. (11) (a) MacDiarmid, A. G.; Chiang, J. C.; Halpern, M.; Huang, W. S.; Mu, S. L.; Somasiri, N. L. D.; Wu, W.; Yaniger, S. I. Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 1985, 121, 173. (b) Chiang, J. C.; MacDiarmid, A. G., Synth. Met. 1986, 13, 193. (c) Lebedev, M. Y.; Lauritzen, M. V.; Curzon, A. E.; Holdcroft, S. Chem. Mater. 1998, 10, 156. (12) Nguyen, M. T.; Kasai, P.; Miller, J. L.; Diaz, A. F. Macromolecules 1994, 27, 3625. (13) Baker, G. L. AdV. Chem. Ser. 1988, 218, 271. (14) (a) Leclerc, M.; Guay, J.; Dao, L. H. Macromolecules 1989, 22, 649. (b) Wei, Y.; Hariharan, R.; Patel, S. A. Macromolecules 1990, 23, 758. (15) (a) MacInnes, D.; Funt, B. L. Synth. Met. 1988, 25, 235. (b) Zotti, G.; Comisso, N.; D’Aprano, G.; Leclerc, M. AdV. Mater. 1992, 4, 749. (16) (a) Nguyen, M. T.; Dao, L. H. J. Electroanal. Chem. 1990, 289, 37. (b) Nguyen, M. T.; Paynter, R.; Dao, L. H. Polymer 1992, 33, 214. (17) (a) Hany, P.; Genies, E. M.; Santier, C. Synth. Met. 1989, 31, 369. (b) Chevalier, J.-W.; Bergeron, J.-Y.; Dao, L. H. Macromolecules 1992, 25, 3325. (c) Bergeron, J.-Y.; Dao, L. H. Macromolecules 1992, 25, 3332. (d) DeArmitt, C.; Armes, S. P.; Winter, J.; Urbe, F. A.; Gottesfeld, S.; Mombourquette, C. Polymer 1993, 34, 158. 71 J. Am. Chem. Soc. 1999, 121, 71-78 10.1021/ja982270b CCC: $18.00 © 1999 American Chemical Society Published on Web 12/19/1998