Poly , emeraldine structure

Asturias et al noted that overoxidized poly aniline will gradually degrade toward the emeraldine structure (in 80% acetic acid solution) due to the hydrolysis of -C=N- double bonds). We find, however, that fully oxidized poly aniline is stable in concentrated sulfuric acid (97%). 

When 0 < y < 1 these structures are the poly(p-phenyleneamineimines), in which the oxidation state of the polymer increases with increasing content of the imine form. The fully reduced form (y = 1) is leucoemeraldine , the fully oxidized form (y = 0) is pernigraniline , and the 50% oxidized structure (y = 0.5) is emeraldine . Each structure can exist as die base or as its salt, formed by protonation, so that we can envisage four repeat units in the polymer chain, in amounts which depend on the extent of both oxidation and protonation of the structure (Fig. 5). 

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). 

Various forms of doped PANI are discussed by Moon el al. [300]. PANls doped with Cl and CIO4" are synthesized in powder form, and HSO4 -doped PANI is obtained by dissolving a Cl -doped form in concentrated H2SO4 and allowing H2O from the atmosphere to precipitate it from this solution. The Cr-doped form is found to be the most crystalline one and to have the most detailed diffraction pattern. The diffraction from the other preparations is similar a structural analysis has not been carried out by the authors. De-doping in aqueous NH OH in this case leads to PANI base with distinct crystallinity, in contrast to results from earlier studies. The similarity between the molecular stnicture of emeraldine base and that of poly(pap-a-phenylene sulphide) and poly(para-pheny-lene oxide) is inferred from common features of the diffraction patterns of the three polymers. 

The structure of the semiconducting emeraldine base form of poly aniline is [(lA)(2A)]n... 

The similarities between the molecular structure of the emeraldine base and those of poly(p-phenylene sulfide),poly(p-phenylene oxide),and even poly(p-phenylene terephthalamide) suggest that a sinular interchain packing might be expect. Indeed, the two strongest equatorial peaks in Figurelb(at 20=19.5 and 20=22.8 ) correspond to the similar peaks observed in all three materials. 

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. 

Both, aniline and anilium hydrochloride were polymerized in direct and in inverse miniemulsion, respectively [140]. The polymerization of anilium hydrochloride, which was initiated by hydrogen peroxide, yielded a highly crystaUine emeraldine polyaniline. In direct miniemulsions, additional stabilizers (e.g., poly(vinyl pyrroU-done) or PVA) were employed to preserve colloidal stability. The polymerization of aniline in direct miniemulsion has also been reported [141] in this case, following polymerization the polymer was first treated with stannous chloride and then doped with p-toluenesulfonic acid. A dramatic increase in conductivity after treatment with stannous chloride was considered due to pernigraniline moiety in the emeraldine base structure having been reduced. Such oxidative polymerization of aniline may be used to add an additional conductive shell to preformed latexes. For example, Li et al. polymerized aniline in the presence of dodecylbenzesulfonic acid on the surface of polyurethane and polyurethane/poly(methyl methacrylate) nanoparticles prepared in miniemulsion [142]. 

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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