Role of Surfactants in the Synthesis of Poly(p-phenylene) Film in Microemulsions Abhijit Manna, † Krisanu Bandyopadhyay, ‡ K. Vijayamohanan, ‡ P. R. Rajamohanan, ‡ S. Sainkar, ‡ and B. D. Kulkarni* ,† Chemical Engineering Division, National Chemical Laboratory, Pune-411008, India, and Physical Chemistry Division, National Chemical Laboratory, Pune-411008, India Received February 18, 1997. In Final Form: August 1, 1997 X Poly(p-phenylene) (PPP), electrosynthesized in different microemulsions by the oxidation of benzene in the form of a uniform and adherent film on Pt surfaces is characterized with a view to understanding the role of different types (anionic, nonionic, cationic) of surfactants. The scanning electron microscopy results reveal distinct morphological changes in the films synthesized with cationic, nonionic, and anionic surfactant systems. The evidence from X-ray photoelectron spectroscopy investigations indicates the incorporation of the sulfur species in the film for the case of cationic surfactant while the anionic and nonionic surfactant systems do not show a sulfur signal. IR investigations of the polymer films show a small degree of cross- linked structure with a long backbone containing aromatic rings irrespective of the surfactant whereas 13 C cross polarization magic angle spinning NMR (solid state) data support the 1,4 substitution (linkage) in the monomer unit in PPP. Differential thermal analysis/thermalgravimetric analysis indicates a higher thermal stability of PPP due to a longer polymer backbone deposited from the anionic surfactant system. The cyclic voltamograms of the films indicate a progressive change in the redox behavior, which correlates well with the relative stability of the intermediate species with a change in surfactant system. Introduction Considerable research efforts during the last 2 decades have resulted in the synthesis of different types of conducting polymers such as poly(p-phenylenes), poly- pyrroles, polyamides, polythiophenes, etc. 1-5 One inter- esting aspect of these materials is the possibility of controlling the electrical conductivity of polymers over a wide range from insulating to nearly that of the best metals, i.e., Cu and Ag. 6 This ability to modulate conductivity and other electronic properties has resulted in several fundamental studies along with many tech- nological applications. For example, oxidation of high molecular weight organic acids such as ascorbic acid is of interest to the food industries owing to its role in assessing food deterioration. 7,8 Electrochemical oxidation of these acids at clean Pt, glassy-carbon, pyrolitic graphite and gold electrodes, however, requires a relatively high overpotential. 9 This problem can be alleviated by the modification of the working electrodes with multilayers of electron-transfer mediators or a polymer which enables the three-dimensional mediator coverage. The latter approach, as exemplified by the use of poly(p-phenylene), polyaniline, polythiophine, poly(p-phenylene sulfide), etc., is more favorable since it provides higher catalytic current. 4 One of the most convenient methods of electrode modi- fication is the electropolymerization to produce a thin conducting polymer film on the electrode surface. 10 PPP is one of the several polymers with a high concentration of aromatic groups in the main chain backbone and the π-conjugation is expected to favor the electron-transfer process. The polymer consists of a linear sequence of phenyl rings having the intrinsic conductivity of 10 -12 S/m (Ω -1 m -1 ), and the conductivity can be increased to around 200 S/m via the formation of charge-transfer complexes or doping. 11-13 Along with the conducting property and inertness toward organic and inorganic solvents, the intrinsic linearity should result in high mechanical strength, at least in the direction of the chain axis. In addition it is a thermally stable and electrically conducting polymeric material and, as a consequence, could be used for several other applications including making of microporous carbon, light-emitting diodes, electron-transfer mediators, lubricant additives, hydraulic fluids, heat transfer agents, etc. 14-17 All these attractive properties of the polymers, however, could not be com- pletely exploited due to the difficulties of synthesis of a free-standing, high-molecular-weight polymer film under normal synthetic conditions. † Chemical Engineering Division. ‡ Physical Chemistry Division. X Abstract published in Advance ACS Abstracts, December 1, 1997. (1) Edwards, G. A.; Goldfinger, G. J. Polym. Sci. 1955, 16, 589. (2) Gamier, F.; Tourillon, G. J. Electroanal Chem. 1983, 148, 299. (3) Bredas, J. L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J. Am. Chem. Soc. 1983, 105, 6555. (4) (a) Nalwa, H. S. In Handbook on conducting Molecules; Wiley: New York, 1996; Vol. 4. 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