Polythiophenes chemical oxidative

Polythiophene can be synthesized by electrochemical polymerization or chemical oxidation of the monomer. A large number of substituted polythiophenes have been prepared, with the properties of the polymer depending on the nature of the substituent group. Oligomers of polythiophene such as (a-sexithienyl thiophene) can be prepared by oxidative linking of smaller thiophene units (33). These oligomers can be sublimed in vacuum to create polymer thin films for use in organic-based transistors. 

SCHEME 2.60 Synthesis of polythiophene via chemical oxidation polymerization. 

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. 

Therefore we have synthesized thiophenes with a fused alkyl ring in the 3 and 4 position of the thiophene moiety and polymerized them either electrochemically or by chemical oxidation. Here the electrochemical, electrical and spectroscopic properties of the obtained polythiophene derivatives are presented. 

Chen et al. reported the synthesis of sulfur/polythiophene composites with core/shell structure through an in-situ chemical oxidative polymerization method for LIB cathode. Using a low viscosity electrolyte of 1,3-dioxolane (DOL)/dimethoxy ethane (DME), the composite with 72 wt% of sulfur was cycled at a current density of 100 mA/g and retained 74% of its initial capacity (1120mAh/g) after 80 cycles [47]. Polythiophene (PTh) coated with ultrathin MnO nanosheets was synthesized through one-step aqueous/ organic interfacial method for LIB anode application. The as-synthesized MnOj-polythiophene nanocomposite delivered a reversible capacity of 720 rnAh/g and retained 500 mAh/g after 100 cycles at a high current density of 500 mA/g [48]. 

Oxidative Poiymerization of Thiophenes. Thiophene is oxidatively polymerized to give polythiophene (PTH) by electrochemical oxidation (237) by chemical oxidation with AsFs (274), NO salts (275), and FeCls (276) and by catalytic oxidation with dioxygen (277). 

V(bithiophene) 1.14 (26) [46]. Electrochemical polymerization of (25) and (26) was possible under conditions close to those for thiophene and (25) and (26) was possible under conditions close to those for thiophene and bithiophene, respectively. Trimethylsilyl groups permitted specific activation of the 2 and 5 positions with respect to the electrochemical oxidation and allowed the preparation of polythiophene films, starting from oligomers, which gave rise to low selectivity without silyl substituents, or monomers with electron-withdrawing substituents. Masuda et al. elec-trochemically polymerized (25), (27) and (28) [47]. Elemental analysis of the resulting films indicated that almost all silicon atoms were eliminated during polymerization. IR spectra, absorption spectra and cyclic voltammometry indicated that the films were made up from polythiophene. Roncali et al. electro-chemically oxidized (29) and obtained a polythiophene film [48]. This particular structure of (29) allows electrochemical preparation to be performed at a very low substrate concentration while the reduction of the silicon to monomer ratio to its minimum value would lead to further improvements in the quality of the polythiophene film. 

The effect of the use of silylmonomers on the structural properties of polythiophene has been established on the basis of Raman and photoluminescence criteria [10,92-4]. In the following two sub-sections, we report the characterizations and data obtained on polythiophenes prepared from electropolymerization and chemical oxidation of a-silylated monomers (Scheme 14.32 and Table 14.10. We are going to focus in particular on experimental data which allow us to stress the role of SiMca groups. 

Polythiophenes have also been prepared by chemical oxidation of a-silylated thiophene and compared to samples prepared from hydrogenated thiophenes [20]. In this section, we focus on the improvement in the structural order and conjugation in polythiophenes resulting from the use of silylated monomers, and on the effect of a thermal treatment on structural order and conjugation of polythiophene. 

Figure 14.21. Low-temperature (7 = 10 K) Raman spectrum of polythiophene prepared from chemical,oxidation of 1-thiophene pTh-Cl and pTh-Cl, 2 = 5145 A.

Figure 14.22. Photoluminescence of polythiophene samples pTh-Cn (n = l,3) prepared from chemical oxidation of hydrogenated -thiophene (a) pTh-C2, (b) pTh-C3, (c) pTh-Cr, . = 5145 A.

Figure 14.25. Raman spectrum of a polythiophene sample prepared from chemical oxidation of a-silylated 4-thiophene, pTh-C4 (a) before thermal annealing, (b) after thermal annealing, A = 5145 A.

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