Poly , emeraldine

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

The common form of polyaniline is a 1 1 combination of alternating reduced (A) and oxidized (C) units it is termed emeraldine (or emeraldine base). The emeraldine base is essentially non-conductive, but its conductivity increases by 9-10 orders of magnitude by treating with aqueous protonic acids. The conductive form of poly aniline can therefore be roughly depicted as a 1 1 combination of alternating A and D units. 

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). 

Fig. 4.6 Schematic diagrams of (a) cyclodextrins, (b) poly-aniline with emeraldine base, and (c) inclusion complex formation of cyclodextrins and a conducting polymer chain insulated molecular wire. (From ref. [32])...

Polymers (CH), PPA Poiy(o-Me3SiPA) PPY DP-PPY PPY PAN PNA EM LM NA PTH PPS PBT PBiT PMeT PHeT PPV PPP P2VP P4VP PVK polyacetylene polyphenylacetylene poly[[o-(trimethylsilyl)phenyl]acetylene] polypyrrole deprotonated (25%) polypyrrole fully reduced polypyrrole polyaniline pernigraniline emeraldine leucoemeraldine nigraniline polythiophene poly(phenylene sulfide) polybenzothiophene poly(2,2 -bithiophene) poly(3-methylthiophene) poly(3-hexylthiophene) poly(phenylene vinylene) poly( p-phenylene) poly(2-vinylpyridine) poly(4-vinylpyridine) poly(A-vinylcarbazole)... 

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). 

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.

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. 

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.

No protons were found to he involved in both the first and second redox reactions of poly(N-methylaniline), but two anions each were taken up for two electrons removed from four aniline units for the oxidation of leucoemeraldine to emeraldine and its further oxidation to the second oxidation state. 

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. 

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