Poly emeraldine salt

Fig. 5.11 Emeraldine forms of polyaniline. (a) Polyemeral-dine base (b) polyemeraldine salt, polaronic form (c) poly-emeraldine salt, bipolaronic form.

A wide range of alkyl- and alkoxy-substituted PAn s of the general types 6 and 7 have been synthesized by the chemical or electrochemical oxidation of appropriately substituted aniline monomers.133 Such substitution imparts markedly improved solubility in organic solvents to the emeraldine salt products compared to the parent (unsubstituted) PAn/HA salts. The poly(2-methoxyaniline) (POMA) species, in particular, has been the subject of extensive studies.134 137 This species has the additional attractive feature of being soluble in water after being wet with acetone. 

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... 

Figure 1,45. Various forms of PANl (a) leucoemeraldine base (LEB, poly(paro-phenylene amine)) (b) pemigraniline base (PNB, poly(poro-phenylene imine)) (c) emeraldine base (EB) (d) emeraldine salt (ES), bipolaron form (e) emeraldine sail, polaron form.

Figure 6.47, The chemical stnictures for (a) poly-acetylenc and polyanilinc in (b) the insulating emeraldine base (EB) form (c) the conducting emeraldine salt (ES) form (d) polythiophene (e) poly(3-mcthylthiophene) and (f) polypyrrole.

To get a moderately high density of carriers per unit volume is relatively easy. For example in poly acetylene, a doping level of 10% per carbon can be achieved, corresponding to a carrier concentration of about 4x10 cm-. This is a typical number for conducting polymers such as polyacetylene, poly(paraphenylenevinylene), poly(paraphenylene), etc. The addition of side chains, as in the poly (3-alky Ithiophenes), reduces the maximum carrier density somewhat, simply because of the smaller fractional volume occupied by the conjugated backbones. For the emeraldine salt of polyaniline, there is one carrier per (B-NH-B-NH)+ repeat unit again n SxlO l. 

Poly aniline (emeraldine salt) can be recovered in partially crystalline form from solutions in sulfuric acid. This is demonstrated by the wide-angle X-ray diffraction pattern of such a poly aniline film, shown as the upper solid curve in Figure la. Essentially identical... 

We have re-analyzed the available data in comparison with the results of band structure calculation to provide the basis for an understanding of the electronic structure of the four principal forms of poly aniline the fuUy reduced leucoemeraldine, (1 A)n the partially oxidized emeraldine base, [(1 A)(2A)]n the oxidized and fully protonat emeraldine salt, [IS] (A )n and the fully oxidized bipolaron lattice, (-B-NH+=Q=NH+-)n. 

The formation of electrically conductive fibers of polyaniline blended with poly(p-phenylene terephthalamide) processed from sulfuric acid was also reported by Hsu et al. [72]. A thoroughly mixed solution of 0.2 wt% emeraldine base and 17.6 wt% poly(p-phenylene terephthalamide) was dissolved in sulfuric acid and this dope solution was extruded at 80°C through a 20-hole spinneret into a 1°C water coagulation bath. The continuous 20 filament yarns that were collected on the bobbin were thoroughly washed with water, which probably led to partial deprotonation of the emeraldine salt. However, the... 

Unlike ring sulfonated polyaniline, the fully sulfonated, water-soluble, polyaniline, poly(2-methoxyaniline-5-sulfonic acid), is shown to be remarkably inert to alkaline dedoping and remains in the conducting emeraldine salt form even in 2.0 M NaOFi [164], The UV-Vis near-infrared spectra of poly(2-methoxyaniline-5-sulfonic acid) solution as a function of plT are shown in Figure 2.28. In water, the absence of a localized polaron band in the range of 750-900 run and presence of a broad absorption in NIR suggests an extended coil conformation... 

Shamon and Fernandes [146] have reported that use of sulphate free poly (styrene sulphonic acid) PSSA as an electrolyte to yield a water soluble poly aniline containing at least 25 C6H4NH units. The evaporation of this aqueous solution yields emerald solid with green metallic lustre. However, on addition of acids like HCl, H2SO4 or their salts in this aqueous solution causes the precipitation of emeraldine salt, suggesting that PSSA is loosely bound to polyaniline. 

Emeraldine base (EB) and emeraldine salt (ES) forms of poly(o-methoxyaniline) (POMA), are able to construct biomolecular hybrids with DNA showing a fibrillar network structure of invariant fibrillar diameter for different hybrid compositions. An approximate model of the Na-DNA/POMA-ES system indicates nanostmctured self-organized assembly of the components in the hybrid [100]. However, the most desired property of fibers for the electronic devices technology is their orientation in a definite direction. Self-assembly of oriented PANI arrays can be achieved in the presence of inorganic acids and by changing the PANI/acid concentration ratio, (Fig. 1.6) [101, 102]. 

Circular dichroism (CD) is a very sensitive spectroscopic tool for probing chain conformations in optically active polymers. For example, with peptides, CD spectroscopy has been widely employed to estimate the proportion of the chain present as the alternative a-helix, P-sheet and random coil conformations. Following our recent discovery of both electrochemical - and chemicaP i routes to chiral PAn.HCSA and related ring-substituted emeraldine salts, we have employed CD spectroscopy extensively to (a) distinguish between "extended coil" and "compact coil" PAn conformations, (b) probe redox and pH switching in PAn, (c) characterize conformational changes in solvatochromism and thermochromism for PAn, and (d) distinguish unequivocally between the conformations/structures of electrochemically and chemically prepared PAn. Similar valuable information on poly-... 

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