Polyaniline and its derivatives

Kahol, P.K., A.J. Dyakonov, and B.J. McCormick. 1997. An electron-spin-resonance study of polymer interactions with moisture in polyaniline and its derivatives. Synth Met 89 1997. 

Polyaniline is the conducting polymer most commonly used as an electrocatalyst and immobilizer for biomolecules [258-260]. However, for biosensor applications, a nearly neutral pH environment is required, since most biocatalysts (enzymes) operate only in neutral or slightly acidic or alkaline solutions. Therefore, it has been difficult or impossible to couple enzyme catalyzed electron transfer processes involving solution species with electron transport or electrochemical redox reactions of mostly polyaniline and its derivatives. Polyaniline is conducting and electroactive only in its protonated (proton doped) form i.e., at low pH valnes. At pH values above 3 or 4, polyaniline is insulating and electrochemically inactive. Self-doped polyaniline exhibits redox activity and electronic conductivity over an extended pH range, which greatly expands its applicability toward biosensors [209, 210, 261]. Therefore, the use of self-doped polyaniline and its derivatives could, in principle. 

In the interval T2 < T < Ty there is a transition from a l-D to a 3-D type of conductivity. Finally, for T < T, the jumps between the chains at the nearest neighbors become important and conductivity is given by Mott s law in three dimensions. It is believed that the behavior of polyaniline and its derivatives can be described by anisotropic three-dimensional variable range hopping (VRH) in the network of metallic rods [61]. Zuppiroli et al. [62] proposed an adiabaticity or multiphonon... 

Polyaniline and its derivatives have been widely used for biosensing applications based on their crystallinity. For example, PANi and its derivatives were found responding to the saturated alcohol vapors by undergoing a change in resistance [54]. The change in resistance of the polymers on exposure to different alcohol vapors was attributed to their chemical structure, chain length, and dielectric nature. 

Polyaniline is a repeating unit of benzene rings each joined by an N—H group (13, Fig. 13.7). This polymer and its derivatives are of interest because they are electrically conductive when doped with oxidants. This material is prepared by oxidation of aniline electrochemically, ° enzymaticaUy, or with simple chemical reagents. Polyaniline can be formally regarded as a polymer of... 

A major goal of the research on conducting polymers has been the development of a rechargeable plastic battery. Cells based on polypyrrole and lithium electrodes have been developed in which the energy per unit mass and discharge characteristics are comparable to nickel-cadmium cells. Current interest appears to center around stable, processable polymers, such as polythiophene and its derivatives, and polyaniline. 

Oxide, flouride, and polymeric films, as well as certain others, are used as protective coatings for HTSC materials (for example, see [505]). The electrodeposition of conducting polymers such as polypyrrole [433,491, 493, 506], polythiophene and its derivatives [493, 507], and polyaniline [478] is the most effective process. Anodic electropolymerization in acetonitrile solutions proceeds without any degradation of the HTSC substrate and ensures continuous and uniform coatings. Apparently, this method is promising not only for the fabrication of compositions with special properties based on HTSC [50, 28,295] as mentioned above, but also for the creation of junctions with special characteristics [507]. 

The system was first applied for development of chemosensors for gaseous hydrogen chloride. Polyaniline, and its copolymers with different derivates of aniline were used. Then a similar approach was tested in the author s group for optimization of amperometric biosensors for glucose based on electrocatalytical detection of hydrogen peroxide. A pigment Prussian blue was used as an electrocatalyst for decomposition of this product of enzymatic oxidation of... 

Athawale A. A. and Kulkarni M. V., Polyaniline and its substituted derivatives as sensor for aliphatic alcohols, Sens. Actuators B, 67, 173-177, 2000. 

Polyaniline and its substituted derivatives, such as poly(o-toluidine), poly(o-anisidine), poly(N-methylaniline), poly(N-ethylaniline), poly(2,3-dimethylaniline), poly(2,5-dimethylaniline) and poly (diphenylamine) have been reported [36] to show measurable responses (sensitivity 60%) for short chain alcohols (viz., methanol, ethanol and propanol) at concentrations up to 3000 ppm. The change (decrease) in resistance of the polymers on exposure to alcohol vapors has been explained based on the vapor-induced change in the crystallinity of the polymer. Polypyrrole (PPy) incorporated with dodecyl benzene sulfonic acid and ammonium persulfate has been reported to show a linear change in resistance when exposed to methanol vapor in the range 87-5000 ppm [37]. The response is rapid and reversible at room temperature. 

Although "polyaniline" has been known for about 150 years, it was not until the mid-1980 s that intense interest in it and its derivatives, as a completely different type of conducting polymer, really began,h3. resulted not only from its ease of synthesis and derivatization, but also from its novel non-redox doping properties and from its potential technological importance. 

Conjugated polymers, such as polypyrrole, pol3d hiophene, polyaniline (PANl) and its derivatives, are the most promising class of organic-semiconducting materials due to their better electrochemical behavior, electrochromism, ease of doping, and synthesis. But, on the other hand the low processability due to its low solubility is a problem. 

Conducting polymers such as polypyrrole [127] and its derivatives [156,157], polyaniline [158-164], polyindole [137] and poly-o-aminobenzoic acid have recently been used for the fabrication of biosensors. A few biosensors based on insulating electropolymerised films like polyphenols, poly(o-phenylenediamine), poly(dichlorophenolindophenol) and overoxidised polypyrrole have also been elaborated [165-167]. ... 

Ext ive investigations on polyaniline (PAn) and its derivatives have be carried out (i) since they possess a moderate conductivity upon doping with protonic acid and an excellent stability under ambient conations (2,3). PAn is simply prepared by the chemical and electrochemical oxidation of aniline or its derivatives in aqueous solution. In general, however, the chemical and electrochemical polymerization of aniline monomer lead merely to an insoluble powder and a thin brittle film, respectively. Hence, it is very difficult to process PAn for a practical use. In order to deal well with this problem, the improvement of processability of PAn has been studied by preparing polymer composites (4) and soluble PAn (5,6) and using plasma polymerization (7) and postsulfonation of PAn (8,9). Another approadi to the preparation of processible PAn is to apply a precursor polymer, e.g., PAn can be produced by the thermal treatment of poly(anthranilic acid) 0 ANA) (10). This mefliod is particularly useful for the preparation of processible PAn or its composites with other insulating polymers since it does not use external dopants that often cause an inconvenient situation associated with a practical use of the conducting polymer. 

Poly(azobenzene) and its derivatives have applications in optical devices [17]. A novel polyaniline containing azo groups was synthesized by the HRP-catalyzed oxidative coupling of 4,4 -diaminoazobenzene (Scheme 1). The polymerization was carried out at pH 6.0 in tris buffer with 70% yield. The polymer analyzed by GPC (80 000, PD = 4.8) was soluble in DMSO and DMF. Azo groups were detected in the main chains as well as in the side chains. Photoexcitation studies indicated that cis-trans isomerization of the chromophore may be the result of structmal constraints in the polymer [ 18). Photodynamic properties of the azo functionahzed polyaniline in their relaxed or constrained conformations were quite different. 

The HRP, aniline (or PANI), and hydrogen peroxide made up a specific oxidative system based on fast reaction kinetics. Devices were developed according to this system in which any two of the three components can be used as a sensor to detect the third component. The electronic signals were collected and analyzed for changes in the electrochemical properties of the polyaniline or its derivatives when the oxidative coupling reactions occurred. Polyaniline-coated polypropylene membranes exhibited strong tendency to adsorb and immobilize HRP [68]. 

An attempt was made to elucidate the structure of these polymers and correlate behaviour with structure. A chlorination reaction taking place during synthesis or doping was indicated by the presence of covalent bonded chlorine in the polymers. The difference in structure and less ionically bonded chlorine over covalent chlorine could be the factors that explained the low conductivity of polymers of diamines, compared with that of polyanilines or its derivatives [5]. 

The use of polypyrrole and its derivatives was investigated soon after the reported discovery of polyaniline membranes. Liang and Martin [65] demonstrated that thin films of polypyrrole could be grown on alumina (An-opore) support membranes by using interfacial polymerization techniques. Doped polypyrrole films were found to be porous, showing Knudsen diffusion with an O2/N2 selection coefficient of 0.94. However, poly(A/-methyl-pyrrole) films were nonporous and showed good gas transport and selectivity. For example, a Ajxm poly(A/-methylpyrrole) film doped with NOs" ions had an oxy-... 

For both types of supercapadtors are required electrode materials having high specific capacitances and quick charge-discharge characteristics. Beside of polyaniline, polypyrrole, also the redoxable PT and its derivatives can be used as efficient materials because of their dopabihty chemically and electrochemically. 

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