Emeraldine polymer

The ability to stretch-orient the emeraldine polymer, as well as the ability to form stretch-oriented fibers of the emeraldine, has enabled the study of conductivity in anisotropically oriented samples [18]. Preliminary studies of oriented ES-II films show that the conductivity increases approximately fifty-fold to a(295 K) 8 S/cm with 2.5. 

Also the case of polyaniline is somewhat different from that of heterocyclic polymers. It has been proposed (MacDiarmid and Maxfield, 1987) that the doping process does not induce changes in the number of electrons associated with the polymer chain but that the high conductivity of the emeraldine salt polymers is related to a highly symmetrical 7r-delocalized structure. 

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). 

Wnek 180> proposed that the structure of the oxidized insulating form of conventionally formed polyaniline is approximately a 50 % copolymer of diamine and diimine units, corresponding to the emeraldine structure and Hjertberg et al.180 obtained CPMAS NMR evidence for this conclusion. Some confirmation of the structure has also been obtained by chemical synthesis of the polymer182). However, Kitani et al.183) have suggested that the normal electrochemical synthesis leads to partially cross-linked polymers. 

Figure 4.6 shows the schematic diagrams of ciclodextrins, polyaniline with emeraldine base, and inclusion complex formation of cyclodextrins and a conducting polymer chain insulated molecular wire. 

More recently, Buchwald has reported the polymerization of the monomer in Eq. (38) [220]. This monomer was polymerized at 80 °C for 24 h in the presence of a catalyst comprised of Pd2(dba)3 and ligand 14. The polymers generated from this monomer bearing a Boc group are soluble in THF and chloroform with the aid of sonication. After isolation, the Boc group could be removed by thermolysis at 185 °C or by protonolysis in air. Emeraldine or the emeraldine salt forms of polyaniline result. 

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)... 

A mixture at 27°C consisting of freshly distilled aniline (0.1097 mol), 85 ml of 3M HCl, 95 ml of ethanol, and LiCl (16 g) was treated with ammonium persulphate (0.0274 mol), 60 ml of 2M HCl, and LiCl (8 g) also at 27°C. The mixture was reacted for roughly 2 hours while the potential of the reaction mixture was controlled by a standard calomel electrode. It was then treated with FeCL (0.0183 mol), LiCl (5 g), and 50 ml of 2M HCl. After an additional hour the reaction was terminated, and the polymer could be isolated by either filtration or by centrifuging. It was then washed with distilled water, dried, and converted to the emeraldine salt using 2M HCl. This salt was then converted to the emeraldine base by treatment with 2 liter of 0.3 M aqueous... 

PAni has a very complex structure and doping behaviour, see Fig. 9.6, and the spectra are sensitive to the polymer morphology, the level of oxidation and degree of protonation. This accounts for the considerable variation in tire spectra that have appeared in the literature. The effects are illustrated in Fig. 9.33 for various forms of the protonated salt. These spectra refer to dried films, electrochemically prepared at different electrode potentials, and subject to oxidation by exposure to air. This variation in preparation conditions means that the degrees of oxidation and protonation are not well defined, as evidenced by the pronounced differences in the spectra of the emeraldine prepared at the... 

For polypyrroles and polythiophenes, n is usually ca. 3 for optimal conductivity, ie. there is a positive charge on every third or fourth pyrrole or thiophene along the polymer chain, near which the dopant anion A is electrostatically attached. For polyanilines, the ratio of reduced (amine) and oxidised (imine) units in the polymer is given by the y/( 1 - y) ratio. The conducting emeraldine salt form of polyaniline has y = 0.5, i.e. there are equal numbers of imine and amine rings present. 

Alternative oxidants such as potassium iodate were also explored for the intrazeolite polymerization of aniline in NaY and acidic forms of Y zeolite. With peroxydisulfate, the polymerization proceeded only if a sufficient supply of intrazeolite protons was available. No polymer formed in either NaY or in acid zeolites with neutral iodate solution, but at low pH polyaniline was obtained in all hosts. The open nature of the zeolite host, even when partially filled with polymer, permits the introduction of base (such as ammonia). On admission of ammonia into the emeraldine salt-containing zeolite, the protonated polymer was converted into the neutral emeraldine base form. 

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