Poly doped conductivity

Polyheterocycles. Heterocychc monomers such as pyrrole and thiophene form hiUy conjugated polymers (4) with the potential for doped conductivity when polymerization occurs in the 2, 5 positions as shown in equation 6. The heterocycle monomers can be polymerized by an oxidative coupling mechanism, which can be initiated by either chemical or electrochemical means. Similar methods have been used to synthesize poly(p-phenylenes). 

Most conducting polymers, such as doped poly(acetylene), poly(p-pheny-lene), and poly(/ -phenylene sulfide), are not stable in air. Their electrical conductivity degrades rapidly, apparently due to reaction with oxygen and/or water. Poly(pyrrole) by contrast appears to be stable in the doped conductive state. 

FIGURE 6.3 Conductivities of doped poly acetylenes conductivities of insulators, semiconductors and metals are given for comparison. 

The grafting of poly-3 methylthiophene (PMeT) on the Pt wire involves the oxidation of the monomer, 3-methylthiophene, 0.5 M in CH3CN + 0.5 M N(C4H9)4S03CF3 at 1.35 V/SCE (satured calomel electrode). The polymer is formed directly in its doped conducting state. This modified electrode is put in a 3 mm-thick electrochemical cell composed of a Teflon ring covered by two Kapton windows. An aqueous copper... 

Poly(ferrocenylene vinylene) derivatives 68 with values of 3,000-10,000 and polydispersities of ca. 2.2-2.8 (determined by GPG) were synthesized in 1995 in high yields via a titanium-induced McMurry coupling reaction of the corresponding alkylferrocenyl carbaldehyde monomers (Equation (26)). " Gharacterization of these soluble polymers by NMR and IR revealed the presence of trans-Yinylcnc units. The UV-VIS spectra of the polymers are similar to those of the monomers and this indicates a fairly localized electronic structure in the former. The relatively limited electron localization is also reflected in the electrical and optical properties. For example, the values for iodine-doped conductivity a= 10 Scm ) and non-linear third-order optical susceptibility (x = 1-4 x 10 esu) are lower than those of linear conjugated polymers such as poly(l,4-phenylene-vinylene) (a = 2.5x 10 Scm" = 8 X 10 esu). 

Table 2.1 The details of various doped conducting poly mers in the metallic state ...

J. R. Reynolds, N. S. Sundaresan, M. Pomerantz, S. Basak, C. K. Baker, Self-doped conducting copolymers - a charge and mass-transport study of poly (pyrrole-co-3-(pyrrol-l-yl)propanesulfonate), /oMr dI of Electroanalytical Chemistry 1988, 250, 355. 

R. S. Wang, L. M. Wang, Z. M. Su, Y. J. Fu, Study of self-doping conductive properties of different oxidized states of poly-3-(2-ethane carboxylate) pyrrole, Synthetic Metals 1995, 69, 511. 

D. Delabouglise, F. Gamier, Poly (3-carboxymethyl pyrrole), a pH sensitive, self-doped conducting polymer, New Journal of Chemistry 1991, IS, 233. 

M. Y. Hua, Y. N. Su, S. A. Chen, Water-soluble self-acid-doped conducting polyaniline poly(aniline-co-N-propylbenzenesulfonic acid-aniline), Polymer 2000, 41,813. 

Wudl and Heeger et al, [17] electrochemically synthesized the sodium salts and acid forms of poly(3-thiophene ethanesulfonate) and poly(3-thiophene butanesulfonate). The monomers 3-thiophene ethanesulfonate and 3-thiophene butanesulfonate were prepared by the route shown in Figure 4.1. However, attempts to electropolymerize these monomers or their sulfonic acid derivatives were not successful. Therefore, the monomers, 3-thiophene alkanesulfonate methyl esters, were polymerized first, followed by conversion of the ester to the sodium salt via the sulfonyl chloride derivative. The sodium salts of poly (3-thiophene ethanesulfonate) and poly( 3-thiophene butanesulfonate) are reportedly soluble in water in their neutral (insulating) and doped (conducting)... 

Similarly to polyaniline and polythiophene, several other self-doped conducting polymers have been explored including polypyrrole, poly(3,6-(carbaz-9-yl) propanesulfonate), poly(p-phenylene), poly(indolecar-boxylic acid), polyphenylenevinylene, and poly(2-ethynyl-N-(4-sulfo-butyl)pyridinium betaine). The details of synthesis and properties are described in the following sections. 

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