Polymers, synthetic electrically conducting

Electrically conductive polymers are just one of a number of esoteric possible uses for synthetic polymers. These materials are now being considered for a variety of applications. 

Synthetic polymers are best known for their insulating dielectric properties which have been exploited for numerous applications in both the electrical and electronic industries. It was found recently that some polymers can also be rendered conductive by an appropriate treatment, thus opening the way to a new field of applications of these materials (2, 3). Usually, electrical conductivity is obtained by doping a neutral polymer, rich in unsaturation, with donor or acceptor molecules. These polymers are rather difficult to synthesize, which makes them very expensive besides they are often sensitive to environmental agents, like oxygen or humidity, thus restricting their practical use to oxygen-free systems. 

The search for new organic metals and superconductors has attracted a great deal of attention in synthetic chemistry and material science since the discovery of high electrical conductivity in conjugated polymers such as polyacetylene [1], Lots of theoretical studies have been carried out in order to understand the mechanism of conductivity and superconductivity in the conjugated polymers and related... 

Many of the applications in which polymers are used are based on the fact that they tend not to conduct an electrical current very well. For example, one reason for the enormous popular success of the first entirely synthetic polymer, Bakelite, in the early 1900s was its outstanding electrical insulation properties, just the characteristic needed for a host of applications in the new and growing held of electrical appliances. Within a decade after its discovery, Bakelite was being used for housing and casings for industrial and household electrical equipment and for insulation on electrical wires and structures. For the past century, the applications of many different kinds of polymers in electrical insulation have become legendary. 

The discovery that doped forms of polypyrroles conduct electrical current has spurred a great deal of synthetic activity related to polypyrroles [216-218], Reviews are available on various aspects of the synthesis and properties of polypyrroles [219,220]. In addition, summaries of important aspects of polypyrroles are included in several reviews on electrically conducting polymers [221-226]. Polypyrrole has been synthesized by chemical polymerization in solution [227-231], chemical vapor deposition (CVD) [232,233], and electrochemical polymerization [234-240]. The polymer structure consists primarily of units derived from the coupling of the pyrrole monomer at the 2,5-positions [Eq. (84)]. However, up to a third of the pyrrole rings in electrochemically prepared polypyrrole are not coupled in this manner [241]. 

Section 3.3 clearly documents the limitations of a molecular description of electrical conductivity. Nevertheless, the molecular and supramolecular architecture of defect-free oligomers provides an easier access to a description of a much more complex situation in polymers. The conclusion to be drawn is that the intrinsic conductivity of conjugated polymers will be even higher than reached up to now, if synthetic procedures succeed in avoiding structural defects (see Sect. 9). 

Electrically conducting polymers, sometimes called synthetic metals, have a backbone that is a rr-conjugated system, with alternating double and single bonds. This system is formed by overlap of carbon 2p -orbitals, as in Figure 7.17. The polymers are named after the monomer units on which their structures are based. The... 

Self-doped PANI are very interesting due to their unique electrochemical behavior unlike PANI, the self-doped polymer remains in its doped state in near neutral or alkaline media [28]. Fully self-doped PANIs are not easy to synthesize due to the lower reactivity of acid-functionalized anilines. Kim et al. [29, 30] introduced an alternative approach in the template-assisted enzymatic polymerization of aniline. Previously, only polyanionic templates had been used for PANI synthesis. However, acid-functionalized anilines bear a net anionic charge in aqueous solution, and attempts to use SPS as template with carboxyl-functionalized aniline resulted in red-brown colored polymers with no polaron transitions, regardless of the synthetic conditions. The use of polycationic templates, such as those shown in Figure 8.2 allowed the synthesis of linear and electrically conductive PANIs with self-doping ability due to the doping effect of the carboxyl groups present in the polymer backbone. 

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