Emeraldine base molecular structure

In the undoped state, PAni is a base. Three molecular structures are possible, one of them being the so-called emeraldine base (EB) shown in Fig. 1 of Chapter 11 [52]. There are several differences between it and the other CP chains discussed above Due to the presence of the N atoms, the chain has a zigzag shape and the benzene rings have either a benzene-like or a quinone-like bond pattern (see Chapter 11, Section IV.B.l) and may be twisted. In principle, the number of independent structural parameters is even larger than for the other CPs. However, quite a good (albeit partial) understanding of the structure has been achieved, as shown in Ref. 24, for instance. 

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 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. 

Figure 14.3 Molecular structure of PANl during protonation/deprotonation process (y=0, insulating fully oxidized pemigraniline base form y=0.5, semiconducting half-oxidized emeraldine base form y=l, insulating fully reduced leucoemeraldine form).

Cavazzoni, C., R. Colle, R. Farchioni, and G. Grosso. 2004. Ab initio molecular dynamics study of the structure of emeraldine base polymers. Phys Rev B 69 115213. 

Most fibers and films of PAn have been prepared from a solution of emeraldine base and converted to the emeraldine salt by acid doping. The choice of dopant acid has a profound effect on mechanical properties. In fact, MacDiarmid et al. have shown that the mechanical properties depend in a complex way on dopant, casting solvent and polymer molecular weight. Full details of the effects of polymer structure (as influenced by dopant and solvent) on the mechanical properties are yet to be eludicated. 

Figure 1.4 Molecular structure of the emeraldine base of polyanlline...

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