The Polyanilines: a Novel Class of Conducting Polymers
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THE POLYANILINES: A NOVEL CLASS OF CONDUCTING POLYMERS ALAN G. MACDIARMID* AND ARTHUR J. EPSTEIN** *Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323 "**Department of Physics and Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1106
ABSTRACT. The synthesis of polyaniline in its fully oxidized, fully reduced and selected average intermediate oxidation states is described together with the synthesis of a self-protonic acid doped polyaniline. The processing of polyaniline films and fibers by thermal stretching to give conductivities up to -100 S/cm is reported. Both doped and undoped polyaniline fibers have tensile strengths approaching those of comnmercial polymers.
INTRODUCTION The term "polyaniline" as commonly employed today [1,2) refers to a class of polymers consisting of up to 1,000 or more (ring-N-) repeat units which can be considered as being derived from a polymer, the base form of which has the generalized composition "
and consists of alternating reduced,
N
and oxidized,-O .=O>Nrepeat units. In principle "y" can be varied continuously from one to give the completely reduced polymer, H to
N
H
0
to zero to give the completely oxidized polymer,
The imine atoms in any of the species can be protonated in whole or in part to give the corresponding salts, the degree of protonation of the polymeric base depending on its oxidation state and on the pH of the aqueous acid. The terms "leucoemeraldine", "emeraldine" and "pernigraniline", used in the following discussion will refer to the different oxidation states of the polymer where y = 1, 0.5 and 0 respectively, either in the base form, e.g. emeraldine base or in the protonated salt form, e.g. emeraldine hydrochloride [1,2]. It seems highly likely that the true average emeraldine oxidation state where y is e equal to 0.5 may never have been synthesized from aniline. The term "emeraldine" in the following discussion will therefore refer to an average oxidation state where y is approximately equal to 0.5 in the generalized formula of the polyaniline bases given above.
SYNTHESIS OF POLYANILINE IN THE EMERALDINE OXIDATION STATE The partly protonated emeraldine hydrochloride salt can be synthesized easily as a partly crystalline black-green precipitate (dark green by transmitted light) by the oxidative polymerization of aniline, (C5H5)NH2, in aqueous acid media by a variety of oxidizing agents, the most commonly used being ammonium peroxydisulfate, (NH4)$208, in aqueous HCI [ 1,3]. As noted in a later section, we have recently shown that the pemigraniline oxidation state
Mat. Res. Soc. Symp. Proc. Vol. 173. 01990 Materials Research Society
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is first formed and that this is subsequently converted to the emeraldine oxidation state. It can
be deprotonated by aqueous ammonium hydroxide to give an essentially amorphous black-blue
(dark blue by transmitted light) "as-synthesized" emeraldine base powder with a coppery,
metallic glint having an average oxidation state corresponding approximately. to tha
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