Conducting polymers head-tail

Summaries on the synthesis, properties, and uses of polythiophenes are included in two general reviews on poly thiophenes [259,260]. A synopsis of important aspects of polythiophenes are also included in several reviews on various aspects of conducting polymers [221-226], Cation radicals are the propagating species in both electrochemical and chemical oxidative polymerizations of thiophene and its derivatives. The polymer obtained by this method is linked primarily by a,a-linkages. However, other types of linkages (a,f3 and /3,/3) are present in varying amounts (Fig. 59). Substituted thiophene derivatives can couple in a head-to-tail or head-to-head manner. 

The formation of -aminodiphenylamine is supposed to be the key intermediate in the formation of a dark green precipitate at the electrode surface during continued electrolysis of acidic aniline solutions. This has been characterized as an oligomer of aniline, for example, as the octamer emeraldine formed by a cascade of head-to-tail condensations [38,39]. Nelson, however, explained it as a mixture of mainly quinhydrone with a small amount of benzidine salt [37]. Today the electropolymerization of aniline under strongly acidic conditions is intensively studied as an important way to form the conducting polymer polyaniline [40] (see Chapters 31 and 32). 

FIGURE 6.9 Illustration of chain structure of poly(3-alkylthiophene) showing effect of head-head (HH) coupling in a mainly head-tail (HT) coupled chain. (From Jeffries-El, M. and McCullough, R.D., in Handbook of Conducting Polymers. Conjugated Polymers. Theory, Synthesis, Properties and Characterisation, 3rd edition, Skotheim, T.A. and Reynolds, J.R. (Eds.), CRC Press, Boca Raton, 2007, 9-1. With permission.)... 

McCullough, R.D. et al.. Self-orienting head-to-tail poly(3-alkylthiophenes) New insights on structure-property relationships in conducting polymers, J. Am. Chem. Soc. 115, 4910 911, 1993. 

McCullough, R.D. 1998. Regioregular, head-to-tail coupled poly(3-alkylthiophene) and its derivatives. In Handbook of conducting polymers, 2nd ed., eds. T.A. Skotheim, R.L. Elsenbaumer, J. R. Reynolds. NewYork Marcell Dekker, pp. 225-258. 

McCullough, R. D., Tristram-Nagle, S., Williams, S. P., Lowe, R., and Jay-araman, M. "Self-Orienting Head-to-Tail Poly(3-alkylthiophenes) New Insights on Structure-Property Relationships in Conducting Polymers."... 

Senkovskyy V, Khanduyeva N, Komber H, Oertel U, Stamm M, Kuckling D, Kiriy A. Conductive polymer brushes of regioregular head-to-tail poly(3-alkylthiophenes) via catalyst-transfer surface-initiated polycondensation. J Am Chem Soc 2007 129 6626-6632. 

In an important discovery in the early 1990s, Cao et al. found that organic solvent solubility can be imparted to conducting PAn salts by the incorporation of surfactantlike dopant acids (HA). For example, by doping emeraldine base (EB) with large bifunctional protonic acids such as camphor-10-sulfonic acid (HCSA) or dodecylbenzenesulfonic acid (DBSA), it is possible to solubilize fractions of these polymers in their fully doped state into solvents such a m-cresol, chloroform, toluene and xylene. This solubilization is caused by the hydrocarbon "tail" in the dopants, while the sulfonate (SO3) "head" forms an ionic bond with radical cation NH.+ sites on the PAn chains. There is some debate as to whether this approach produces true "solutions" or forms dispersions in organic media. In practical terms, the result is the same solution-processible unsubstituted conducting polymers in the doped state. 

The microstructure and architecture of polymers can also gready influence die properties of die polymers. For example, poly(3-substituted thiophene)s could have three microstructure joints s-trans (head to tail), s-trans (head to head), and s-cis (head to tail) (Fig. 9.3). The regioregular head-to-tail poly(3-substituted thiophene)s exhibit higher electrical conductivity values and higher... 

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