Polyaniline emeraldine base sulfonated

Han et al. [64, 66] reported the synthesis of highly conductive and thermally stable self-doped mercaptopropanesulfonic-acid-substituted polyanilines by the concurrent reduction and substitution reaction between polyaniline and a nucleophile. These reactions were carried out on both electrochemically generated and free standing polyaniline films prepared from emeraldine base dissolved in N-methylpyrrolidinone. The electrochemically prepared films were dedoped with 5 % aqueous NaiCOs to convert them the into the emeraldine base form. The sulfonated polyaniline was prepared by reaction of a polyaniline emeraldine base film with 0.1 M 3-mercapto-l-propanesulfonic acid sodium salt in methanol under nitrogen at room temperature for approximately 14h [66]. A catalytic amount (0.01 M) of acetic acid was reported to accelerate the reaction. The resulting sulfonated polyaniline film was thoroughly rinsed with methanol, followed by 5 % aqueous NaiCOs to remove reactants. 

Figure 2.21 pH dependence of DC conductivity at room temperature for leu-coemeraldine-base sulfonated polyaniline (O), emeraldine-base sulfonated polyaniline (0) and polyaniline-HCl (A). (Reprinted with permission from Journal of the American Chemical Society, 118, 2545. Copyright (1996) American Chemical Society.)... 

Figure 2.29 N Is X-ray photoelectron spectra of (A) self-doped emeraldine base sulfonated polyaniline (50 %) and (B) polyaniline doped with HCl. (Reprinted with permission from Macromolecules, 24, 4441. Copyright (1991) American Chemical Society.)...

Magnetic susceptibility and electron spin resonance data of self-doped sulfonated polyaniline shows the presence of Curie like susceptibility and temperature independent Pauli like susceptibility. The product of the spin susceptibility and temperature (xT) versus temperature for the emeraldine base sulfonated polyaniline is shown in Figure 2.30 [41]. Based on the Pauli spin concentration, the density of states at the Fermi level N( f) (from the slope) is 0.8 state/eV-two rings and an effective Curie spin concentration (from the T = 0 intercept) is 0.02 spin/two... 

Polyaniline emeraldine base could be converted to sulfonated polyaniline (Fig. le), a self-doped, water-soluble conducting polymer [27,28]. Without external doping, this polymer has a conductivity of 0.1-1 S/cm. This polymer has better thermal stability than PANI-HCl. Membranes made from this polymer could have electrochemically controllable acidity and enzyme activity. 

We have prepared a series of nylon / poly aniline blends using the solvent hexafluoroisdpropanol (HFIP), which is an excellent solvent for polyaniline emeraldine base (PANI-EB), polyaniline doped with various sulfonic acids (PANI-ES) and for hi molecular weight nylon 6 and nylon 12. It was observed that conductivity and morphology of the blends varied with the compatibility of the sulfonic acid anion with the nylon. Methanesulfonic acid, butane sulfonic acid dodecylbenzene sulfonic acid and camphor sulfonic acid were used as PANI dopants and the PANI-ES / nylon blends were characterized by electrical conductivity (room and low temperature) and transmission electron microscopy. The results of these various measurements and the conclusions which can be drawn regarding morphology and conductivity of Ihe blends, will be reported. 

FIGURE 1.2. Molecular structure of widely used it-conjugated and other polymers (a) poly(para-phenylene vinylene) (PPV) (b) a (solid line along backbone) and it ( clouds above and below the a line) electron probability densities in PPV (c) poly(2-methoxy-5-(2 -ethyl)-hexoxy-l,4-phenylene vinylene) (MEH-PPV) (d) polyaniline (PANI) (d.l) leucoemeraldine base (LEB), (d.2) emeraldine base (EB), (d.3) pernigraniline base (PNB) (e) poly(3,4-ethylene dioxy-2,4-thiophene)-polystyrene sulfonate (PEDOT-PSS) (f) poly(IV-vinyl carbazole) (PVK) (g) poly(methyl methacrylate) (PMMA) (h) methyl-bridged ladder-type poly(jf-phenylene) (m-LPPP) (i) poly(3-alkyl thiophenes) (P3ATs) (j) polyfluorenes (PFOs) (k) diphenyl-substituted frares -polyacetylenes (f-(CH)x) or poly (diphenyl acetylene) (PDPA). 

FIGURE 9.1. Repeat units of the pyridine-containing polymers and other polymers used in the study (a) poly(p-pyridine) (PPy) (b) poly(/ -pyridyl vinylene) (PPPyV) (c) copolymer of PPY and PPyV [PPyVP(R)2V] (d) wrapped copolymer of pyridylvinylene and penylenevinylene ( PPyVPV) (e) wrapped copolymer of dithienylene and phenylene ( PTP) (f) emeraldine base (EB) form of polyaniline (g) sulfonated polyaniline (SPAN). 

Fig. 3. (a) Polyorthotoluidene (emeraldine base form) (b) sulfonated polyaniline (self-doped salt form). 

Electrophilic substitution is a straightforward way to functionalize polyaniline. Substitution of sulfonic acid groups on the backbone of polyaniline, as shown in Figure 2.2, was first introduced by Epstein et al. [39] in the very first report of self-doped water soluble polyaniline. Their synthetic method involved the sulfonation of polyaniline using fuming sulfuric acid. The emeraldine base form of polyaniline (0.5 g) was dissolved in 40 mL of fuming sulfuric acid with constant stirring. 

FIGURE 1 Polyanilines in different forms and dilferenl oxidation states, (a) Leucoemeral-dine base (LEB) (b) emeraldine base (EB) (c) pemigraniline base (PNB) (d) emeraldine salt (ES-HCSA) and (e) sulfonated polyaniline (SPAN). 

Figure 20.42. Emeraldine hydrochloride (I) emeraldine base (II) ring-sulfonated, protonated, polyaniline (III) and ring-sulfonated, non-protonated sodium forms of polyaniline (IV).

Self-doping was eonfirmed by the similarity between absorption speetra of the sulfonated polyaniline and the emeraldine hydrochloride form (Figure 20.44). The effect of the sulfonate group on steric interactions between adjacent rings is evident from the blue shift in the absorption spectra of the sodium salt of the non-protonated sulfonated derivative compared to the emeraldine base (Figure 20.45). 

Figure 20.45. Absorption spectra of ring-sulfonated polyaniline in aqueous NaOH ( —) and non-sulfonated emeraldine base in NMP (----). (Reprinted by permission of ref 37)...

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