Emeraldine form, polyaniline

Wnek 180> proposed that the structure of the oxidized insulating form of conventionally formed polyaniline is approximately a 50 % copolymer of diamine and diimine units, corresponding to the emeraldine structure and Hjertberg et al.180 obtained CPMAS NMR evidence for this conclusion. Some confirmation of the structure has also been obtained by chemical synthesis of the polymer182). However, Kitani et al.183) have suggested that the normal electrochemical synthesis leads to partially cross-linked polymers. 

Chiang J, MacDiarmid AG (1986) Polyaniline protonic acid doping of the emeraldine form to the metallic regime. Synth Met 13 193-205... 

The formation of -aminodiphenylamine is supposed to be the key intermediate in the formation of a dark green precipitate at the electrode surface during continued electrolysis of acidic aniline solutions. This has been characterized as an oligomer of aniline, for example, as the octamer emeraldine formed by a cascade of head-to-tail condensations [38,39]. Nelson, however, explained it as a mixture of mainly quinhydrone with a small amount of benzidine salt [37]. Today the electropolymerization of aniline under strongly acidic conditions is intensively studied as an important way to form the conducting polymer polyaniline [40] (see Chapters 31 and 32). 

The synthesized produet was a powder by green color that indicates about production of the emeraldine form of polyaniline, exactly emeral-dine salt Vkn-HCl. The produced samples of PAn/nano-Ti02- S composites had more light tinctures their intensities were decreased with the increasing of the TiO content in the initial reaction mixture. 

T. Akai, T. Shimomura, and K. Ito, HCl-doping of insulated molecular wire formed by emeraldine base polyaniline and molecular nanotube, Synth. Met., 135, 777-778 (2003). 

From the date recorded on oligomers, we have also studied in details the protonated emeraldine form of the polyaniline and have clarified the delocalization of the charged defects along the chain as a function of the solution acidity. 

In this paper, we have investigated the electronic structure of different base forms of polyaniline by using X-ray photoelectron spectroscopy. The protonated emeraldine form has been also investigated to determine the charge delocalization along the chain as a function of the pH. 

In a first step, the electronic structure of the polyaniline base form has been followed versus the oxidation state. After that, we have proceeded further with the protonated emeraldine form. In all cases, the binding energy scale has been calibrated by setting the Cls core level main peak at 284.4 eV. 

In a second part, the electronic structure of the protonated emeraldine form of polyaniline have been analysed and in particular theNls core level. 

The conductivity of the emeraldine salt increases with decrease in pH of the acid used to dope it. In this respect, polyaniline, in its emeraldine form, differs from other conductive polymers because it does not require partial oxidation or reduction for doping. Protonation of the imine nitrogens is sufficient to make it a very conductive material. 

J.-C. Chiang, A. G. MacDiarmid, Polyaniline Protonic Acid Doping of the Emeraldine Form to the Metallic Regime. Synth. Met. 1986, 13, 193-205. 

H. Javadi, K. Cromack, A. MacDiarmid, A. Epstein, Microwave Transport in the Emeraldine Form of Polyaniline. Phys RevB 1989,39,3579-3584. 

Polyaniline can undergo a reversible acid/base doping/dedoping process. In the emeraldine salt form, polyaniline is conductive. This form can then be converted to the insulating emeraldine base form of polyaniline, upon exposure to base as in Equation 1, where HX is a protonic acid ... 

Fig. 5 Scheme of redox transformations and protonation equilibria of polyaniline where L, E, P, LHgx, EHgx represent different oxidation and protonation states. E - leucoemeraldine, E - emeraldine, P - pernigraniline, LHgx - protonated leucoemeraldine, EHgx - protonated emeraldine forms. 

---