Polyaniline ring-sulfonated

A different method of S3mthesizing polyanUine was reported [77]. It uses an enzyme, horseradish peroxidase, in the presence of hydrogen peroxide to polymerize aniline. To prevent reactions at the ortho positions of the phenyl rings that yield insoluble branched materials, a polyelectrolyte template, like sulfonated polystyrene, was used. The polyelectrolyte aligns the monomers, dopes the polyaniline to the conducting form, and forms an irreversible complex with the polyaniline to keep it water-soluble [77]. The conductivity of the complex increases with increasing polyaniline to sulfonated polystyrene molar ratios. Conductivities of0.005 S/cm are obtained with the pure complex and increase to 0.15 S/cm after additimial doping by exposure to HCl vapor [77]. 

Figure 1.17 Chemical structures of (A) self-doped ring-sulfonated poly aniline and (B) dedoped (insulating) salt form of ring-sulfonated polyaniline. (Reprinted with permission from Journal of the American Chemical Society, 112, 2800. Copyright (1990) American Chemical Society.)...

Epstein et al. [41, 54, 71] suggested that the sulfonated polyanilines have much stronger temperature dependence conductivity than emeraldine hydrochloride due to greater electron localization. The temperature dependence of the conductivity of 50 % [41], 75 % [54] and fully ring sulfonated polyanilines [71] was best fit by the quasi one-dimensional variable range hopping model described by Equation (2.1) ... 

The half wave potential, 1/2 of the first and second redox processes of 50 % ring sulfonated polyaniline as a function of pH range are shown in Figure 2.24. Both redox processes are found to depend on the solution... 

Figure 2.26 UV-Vis absorption spectra of 50 % ring sulfonated polyaniline film...

Unlike ring sulfonated polyaniline, the fully sulfonated, water-soluble, polyaniline, poly(2-methoxyaniline-5-sulfonic acid), is shown to be remarkably inert to alkaline dedoping and remains in the conducting emeraldine salt form even in 2.0 M NaOFi [164], The UV-Vis near-infrared spectra of poly(2-methoxyaniline-5-sulfonic acid) solution as a function of plT are shown in Figure 2.28. In water, the absence of a localized polaron band in the range of 750-900 run and presence of a broad absorption in NIR suggests an extended coil conformation... 

G. Niaura, R. Mazeikiene, A. Malinauskas, Structural changes in conducting form of polyaniline upon ring sulfonation as deduced by near infrared resonance raman spectroscopy, Synthetic Metals 2004, 145, 105. 

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

Figure 20.43. pH dependence of conductivities of ring-sulfonated poly anilines ( ) and emeraldine hydrochloride form of polyaniline (O). (Reprinted by permission of ref. 37)... 

In contrast to ring-sulfonation of polyaniline, Bergeron et al. derivatized the leucoemeraldine form of poly aniline at the N-position with an alkylsulfonate group as shown in Figure 20.46 [38]. The sodium salt was achieved by reacting the leucoemeraldine base with NaH and 1,3-propanesultone. 

A number of water-soluble polyaniline derivatives have been developed in recent years. Incorporation of sulfonate groups onto the polymer backbone imparts water solubility to the polymer. In one process, this is accomplished by treating the polymer with fuming sulfuric acid which results in a sulfonic acid ring-substituted derivative that is alkali soluble but only upon conversion to the nonconducting sulfonate salt form. 

A major advance in the solubilization of polyaniline was self-doping by the attachment of a sulfonic acid side group to the backbone ring [47,48]. The resulting material is essentially a polyzwitterion with the acid proton transferring to the basic amine backbone. The polymer is then soluble in mildly basic aqueous solutions and can be coated over large areas. 

Substitution with an electron acceptor, such as chlorine for poly(2-chloroaniline) (33a), yields polymers that switch between yellow in the neutral form to blue in the oxidized form [122]. Sulfonic acid ring-substituted polyaniline (33b) can be prepared by direct chemical reaction of polyaniline with concentrated sulfuric acid [132]. This polymer film switches from transmissive yellow to blue even in solutions of elevated pH up to 7. 

Li, C. and S. Mu. 2004. Electrochromic properties of sulfonic acid ring-substituted polyaniline in aqueous and non-aqueous media. Synth Met 144 143-149. 

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