conducting polymers are produced when a nonconducting polymer is blended with a

conducting polymer physically or chemically. The conductivity of the resulting product

is improved.

19.3 Common Examples of Conducting Polymers

19.3.1 Polyaniline (PANi)

Polyaniline is a conducting polymer that is produced from the oxidative polymerization of

aniline. The polymer backbone of polyaniline is composed of both quinoid and benzoid

rings in different ratios. The differences in the proportions of quinoid and benzoid ring

results in the existence of polyaniline in three different oxidation states. The three different

forms of polyaniline are emeraldine, pernigraniline, and leucoemeraldine. Polyaniline in

the conductive emeraldine form consist of equal proportions of both quinoid and benzoid

rings. In the fully reduced leucoemeraldine form, polyaniline is composed of quinoid rings

whereas the fully oxidized pernigraniline form of polyaniline consists of benzoid rings.

Emeraldine is the most important form of polyaniline because it is electrically conductive.

Emeraldine is produced from the oxidative polymerization of aniline in aqueous acids. This

form of polyaniline is also stable as the positive charge units on the aniline are balanced by

the negative charges of the chloride ion in the structure. Figure 19.3a-b depicts the structure

of polyaniline and its forms.

Several forms of polymerization have been employed in the synthesis of polyaniline.

These include electrochemical polymerization, chemical polymerization, plasma poly­

merization, and interfacial polymerization. Wang et al. [1] used an electrochemical poly­

merization approach to synthesize polyaniline. They reported that the electrochemical

FIGURE 19.3

Chemical structures of conducting polymers. (a) Polyaniline, (b) molecular forms of polyaniline; I. Leucoemeraldine.

II. Emeraldine III. Pernigraniline, (c) polyacetylene, (d) poly(3,4-ethylene dioxythiophene), (e) polypyrrol,

(f) polyfuran, and (g) polythiophene.

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