Doped conducting polymers are grouped into p-doped and n-doped conducting

polymers. In p-doped conducting polymers, as shown in Figure 19.2a, when polymers

with conjugation in the backbone are treated with electron-deficient species (Lewis

acids), oxidation occurs, causing the formation of a positive charge in the polymer. The

removal of one electron from the π-backbone of the conjugated polymer results in

the formation of a radical cation (polaron). Losing a second electron forms bipolaron.

The delocalization of the positive charges is responsible for the electrical conduction. In

n-doped conducting polymers, as shown in Figure 19.2b, when the Lewis base is

reacted with a conjugated polymer, the reduction of the polymer leads to the formation

of a negative charge. By the addition of the first and second electrons, polaron and

bipolaron are formed, respectively. The delocalization of the charge causes conductive

behavior.

In extrinsically conducting polymers, the conductivity of these polymers is due to the

addition of external ingredients. In one type, non-conductive polymers act as binders

impregnated with conducting elements like metals to form a single solid polymer filled

with the conductive material. The presence of the conductive element confers con­

ductivity on the product. The minimum concentration of the conductive filler added to

let the polymer start conducting is called the percolation threshold. In another group,

FIGURE 19.1

Classification of conducting polymers (CPs).

FIGURE 19.2

An illustration of the chemical reaction leading to the formation of doped conducting polymers. (a) p-type and

(b) n-type conducting polymer.

Conducting Polymer Composites

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