Polyaniline leucoemeraldine base form

Figure 4-1. Chemical structures of conducting polymers, (a) Frans-polyacetylene (b) cw-polyacetylene (c) poIy(/i-phenylene) (d) polypyrrole (e) polythiophene (f) poly(/>-phenylenevinylene) (g) poly(2,5-thienylenevinylene) (h) polyaniline (leucoemeraldine base form) (i) polyisothianaphthene.

Leucoemeraldine base, the completely reduced form of polyaniline base, can be controllably oxidatively doped to the highly conducting regime/analogously to (CH)x,viz.,... 

It has recently been observed31 that the completely reduced base form of polyaniline, (leucoemeraldine), spontaneously reduces, and is itself oxidized, when its solution in NMP is mixed with an NMP solution of the completely oxidized base form of polyaniline, (pernigraniline). This reaction may be studied by "titrating" a solution of the leucoemeraldine with a solution of pernigraniline and by following the course of the reaction by the changes in the electronic spectrum of the reaction mixture. When equimolar solutions of the reactants are mixed this redox reaction is found to approach equilibrium after 20 hours at room temperature, to produce the emeraldine base, viz.,... 

The emeraldine salt of polyaniline which is one of the three different forms of polyaniline—leucoemeraldine (the fully reduced state], emeraldine (the half oxidized state] and pernigraniline (the fully oxidized state] (Fig. 8.1]—is electrically conductive while the others are insulators. Conventional chemical synthesis of polyaniline is based on an oxidative polymerization of aniline by using an oxidant in the presence of a strong acid dopant in the reaction mediunL ... 

In contrast to ring-sulfonation of polyaniline, Bergeron et al. derivatized the leucoemeraldine form of poly aniline at the N-position with an alkylsulfonate group as shown in Figure 20.46 [38]. The sodium salt was achieved by reacting the leucoemeraldine base with NaH and 1,3-propanesultone. 

The chemical structure of polyaniline in various oxidation states is shown in Figure 3. The fully reduced form is referred to as leucoemeraldine base (LEB) while the fully oxidized form is called pemigraniline (PNB). Both LEB and PNB will shift towards the EB form upon exposure to an oxidizing environment.[2] Although it is well known that the oxidation state of polyaniline is an important characteristic of this polymer, there are few reports of its influence on the development of morphology in fibers and films. Previous work has shown that both films and fibers produced from solutions of leucoemeraldine base in N,N -dimethyl propylene urea (DMPU) exhibit crystallinity and a melting transition.[12]... 

Polyaniline, one of the most studied conducting polymers (in general as well as for corrosion protection), is usually obtained by protonation of what is called the emeraldine base form, shown in Figure 2. The protonation reaction does not change the number of electrons in the polymer backbone. However, starting at the leucoemeraldine form of polyaniline, one would obtain the emeral e salt (conducting) form of polyaniline by an oxidation reaction. Protonic doping has also been observed in the case of alkoxy substituted poly(para-phenylene vinylene) (PPV) ... 

Polyanilines formed by both the chemical and electrochemical processes have been extensively studied to establish structure-property relationships. In this section, the structural studies of polyaniline are reviewed and the influence of structure on properties is considered in Chapter 5. The description of polyaniline structure is complicated by its complexity. As described above, polyaniline can exist in six different forms (the salt or base forms of leucoemeraldine, emeraldine and pernigraniline). In addition, the proto-nated forms of polyaniline also have counter-anions intimately associated with the positively charged polyaniline chains. Finally, it has also been observed that polyanilines may contain considerable amounts of solvent molecules. 

Fig. 1. (a) Leucoemeraldine base (b) emeraldine base (c) pernigraniline base (d) polyCparaphenylene sulfide) le) emeraldine hydrochloride salt polymer (f) poly(orthotoluidine) (emeraldine base form) (g) sulfonated polyaniline (self-doped salt form). 

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