Self-doped polymers

IV. SELF-DOPED POLYMERS, POLYMERIC COMPOSITES, AND HYBRID MATERIALS... 

Self-doped polymers, 334 Semicircles, Albery and Mount interpretation of, 584 Semiconductor electrodes with polymer layers, 499 diffusion length in, 492 Semiconductors, lifetime for carriers and, 495... 

The related fully sulfonated, self-doped polymer poly(2-methoxyaniline-5-sulfonic acid) (PMAS 9) may be prepared under normal atmospheric pressure by the oxidation of 2-methoxyaniline-5-sulfonic acid (MAS) monomer with aqueous (NH4)2S208 in the presence of ammonia or pyridine (to permit dissolution of the MAS monomer).141 The polymerization pH was therefore >3.5. Subsequent studies showed that the product consisted of two fractions a major fraction with Mw of ca. 10,000 Da whose electrical conductivity and spectroscopic and redox switching properties were consistent with a PAn emeraldine salt, as well as a nonconducting, electroinactive oligomer (Mw ca. 2,000 Da).143 144 Pure samples of each of these materials can be obtained using cross-flow dialysis.145... 

The self-doped polymer, poly A-(4-sulfophenyl)aniline 10, bearing a sulfonated substituent on each of its N centers, has also been prepared by oxidizing the relevant monomer with (NH4)2S208 in aqueous HC1.146 147 Phosphonic acid substituents can also be utilized to generate self-doping PAn s, as illustrated by the oxidation using... 

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. 

As the degradation of polyaniline occurs via an imine intermediate [281,284], Kim et al. [285] prepared self-doped polymer by alkylsulphonate substitution in the polymer backbone, Besides self-doping for a facile redox process, the perceived advantage of this bulky substituent includes the protection of nitrogen centres from nucleophiles responsible for irreversible degradation of polyaniline. Poly(aniline N-butylsulphonate) retained its reversible electrochromic response up to 150 000 cycles when scanned between its oxidized and reduced states (between 0.2 and 0.5 V) then started diminishing slowly. The excellent redox cyclability of poly(aniline N-butylsulphonate) over unsubstituted polyaniline was also confirmed by chronoabsorptom-etry by Kim et al. [285],... 

Self assembly, 679 Self-doped material, 837 Self-doped PANl, 65 Self-doped polymer, 853 Semiempirical PM-3 Semiquinone radical, 214 Sensors, 833 Setting angle, 9, 255 para-Sexiphenyl deposition, 36 Sexidriophene, 93 Shelf-life, 802 Shielding levels, 370 Shielding properties, 369... 

In an attempt to produce carbazole polymers soluble in aqueous solutions, oligoether groups have been attached to the carbazole unit at the iV-position (28d) and the polymer prepared by chemical polymerization and electrochemical polymerization [105]. Due to the oligoether substituents, electrochemical polymerization can occur in aqueous solutions without the need for a cosolvent. Polymer films switch between a highly transmissive state to deep green upon oxidation. The self-doped polymer, poly[3,6-carbaz-9-yl)propanesulfonate] (28e), has also been produced, which is water-soluble and switches from a transmissive neutral state to a dark green oxidized state [106]. 

Qiu, Y.-J. and J.R. Reynolds. 1990. A self-doped polymer with both cation and anion exchange properties. / Electrochem Soc 137 900-904. 

Soluble conducting polymers can be solvent cast to form coatings. The addition of appropriate substituents to the polymer backbone or to the dopant ion can impart the necessary solubility to the polymer. For example, alkyl or alkoxy groups appended to the polymer backbone yield polypyrroles [117,118], polythiophenes [118], polyanilines [119,120], and poly(p-phenylenevinylenes) [97] that are soluble in common organic solvents. Alternatively, the attachment of ionizable functionalities (such as alkyl sulfonates or carboxylates) to the polymer backbone can impart water solubility to the polymer, and this approach has been used to form water-soluble polypyrroles [121], polythiophenes [122], and polyanilines [123]. These latter polymers are often referred to as self-doped polymers as the anionic dopant is covalently attached to the polymer backbone [9]. For use as a corrosion control coating, these water-soluble polymers must be cross-linked [124] or otherwise rendered insoluble. 

These reaction formulae indicate that the electron transfer taking place at the metal I polymer interface is accompanied by ionic charge transfer at the polymer Isolation interface, in order to maintain the electroneutrality within the polymer phase. Counterions usually enter the polymer phase, as shown above. However, less frequently the electroneutrality is established by the movement of co-ions present in the polymer phase, e.g., in so-called self-doped polymers. Oxidation reactions are often accompanied by deprotonation reactions, and H+ ions leave the film, removing the excess positive charge from the surface layer. It should also be mentioned that simultaneous electron and ion transfer is also typical of electrochemical insertion reactions however, this case is somewhat different since the ions do not have lattice places in the conducting polymers, and both cations and anions may be present in the polymer phase without any electrode reaction occurring. The es-... 

A distinctive property of self-doped polymers is their water solubility in the neutral (insulating) and doped (conducting) states. This solubility is due to the covalently attached negatively charged groups on the polymer backbone. Solubility allows a deposition of conductive and electroactive layers onto any, even a nonconducting, surface by a simple casting of self-doped polymers. Such layers could find numerous applications... 

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