Conjugated conducting polymers Polypyrrole

Poly 1 -(trimethylsilyl)-1 -propynel Conjugated conducting polymers Polypyrrole Polythiophene... 

Conjugated conducting polymers have been found in some cases to present by themselves an intrinsic electrocatalytic activity. Among the few examples, polypyrrole has been shown to be an interesting catalyst for the quinone-hydroquinone redox system [34,35] or for the electro-reduction of dioxygen [36]. 

Conducting polymers are chemically characterized by the so-called conjugation, in which carbon double bonds alternate with carbon single bonds along a polymer backbone. The chemical structures of two examples of conducting polymers, polypyrrole (PPy) and polyaniline (PANi), are reported in Fig. 6.101. 

In the context of this chapter, we focus on the undoped or lightly doped 7i-conjugated systems that are commonly referred to as organic semiconductors. Conducting polymers, such as PEDOT PSS, plexcore, polyaniline, polypyrrole, and others are not addressed here as their charge transfer mechanisms are rather different and would warrant an article in its own right. 

Solitons are considered to be important defect states in these conjugated polymers (see Fig. 6.48). It has however been shown that correlation energy is the more important factor in giving rise to the energy gap in (CH) (Soos Ramasesha, 1983). Other polymers related to polyacetylene are polythiophene, polypyrrole, poly-phenylenesulphide, and polyparaphenylene (Section 3.3). Extensive measurements on doped polyacetylenes have been reported in the last five years and these materials, unlike other conducting polymers such as (SN), seem to have good technological potential. 

Keywords Conducting polymers, Conjugated polymers, Polyacetylenes, Polyanilines, Polypyrroles, Polythiophenes, Poly(arylene vinylenes), Polyphenylenes... 

Although the original research on conductive polymers was done with polyacetylene, a number of other conjugated polymers have been developed for such uses. Among these products are the polythiophenes, polyanilines, polyphenylenevinylenes, polyethylene-dioxythiophenes, polypyrroles, and polydialkylfluorenes. These products are now beginning to find applications in a number of industrial, research, medical, and consumer devices. 

Many other air-stable conducting polymers followed (Fig. 12.10) polypyrrole, polythiophene, polyaniline (which had been known since the nineteenth century as "aniline black"), and so on (Table 12.4). These polymers are semiconducting, not metallic, when "doped" with electron donors or acceptors the individual conjugated chains have finite length, so the conductivity is limited by chain-to-chain hopping. Also, if the individual strands exceed four or so oligomers, the conjugation tends to decrease, as the strand tends to adopt a screw-type distortion. The transport within each strand is attributed to polarons and bipolarons. 

The first conducting polymer was trans-polyacetylene which was doped with bromine and was produced at 1970s. Soon other conjugated polymers such as poly (p-phenylene), polypyrrole (PPy), polyethylene dioxythiophene (PEDOT) and polyaniline (PANi) and their derivatives which are stable and processable were synthesized. The molecular structures of a few ICPs are shown in Figurel. 

Properties of representative conducting polymers. Doped conjugated polymers have generated substantial interest in view of possible applications such as lightweight batteries, antistatic equipment, and microelectronics to speculative concepts such as molecular electronic devices.37-38 These polymers include doped polyacetylene, polyaniline, polypyrrole, and other polyheterocycles (Figure 5). While the conduction mechanism of metals and inorganic semiconductors is well understood and utilized in microelectronics, this is not true to the same... 

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