Polyanilines secondary doping

The nitrogen-containing conductive polymers, polypolypyrrole (PPY) and polyaniline (PAN) in particular, have been of great interest because of their controllable electrical conductivity, environmental stability and interesting redox properties associated with the chain heteroatoms, More importantly, the century-old [57,58] aniline family of polymers has been found to exhibit solution [59,60] and counter-ion induced [61-63] processability. Furthermore, the electrical properties of the aniline polymers can be substantially improved through secondary doping [64]. The aniline polymers have the general formula [(-B-NH—B—NH—), (-B—N=Q=N-)i.,.]v, in which B and Q denote the... 

Xia, Y, Wiesinger, J. M., MacDiarmid, A. G., and Epstein, A. J., Camphorsulfonic acid doped polyaniline emeraldine salt conformations in different solvents studied by a UV/visible/near-infrared spectroscopic method, Chem. Mater., 7, 443-445 (1995), Min, Y, Xia, Y, MacDiarmid, A. G., and Epstein, A. J., Vapor phase secondary doping of polyaniline, Synth. Met., 69, 159-160 (1995). 

To explain the unusually high conductivity of these polyblends of polyaniline Min et al. [112,113] have suggested secondary doping, which has been defined as an inert substance (vapour or liquid) which promotes the conductivity of an already doped form of the conducting polymers. These may also induce molecular conformational changes to reduce conjugation defects resulting in increased intramolecular conductivity and may also enhance crystallinity. It has been observed that in the absence of w-cresol the conductivity of camphor sulphonic acid-doped polyaniline film is... 

To obtain fully doped polyaniline salt, the molar ratio of EB to the dopant (CSA) should be 1 2, assuming that all of the dopant ions successfully protonate an imine nitrogen. For example, 1.0 g (0.00276 mol) of EB would be mixed with 1.287 g (0.00552 mol) of HCSA. The EB and HCSA was mixed in two different ways. For some films, the EB and HCSA were mixed as powders using a mortar and pestle. This doped EB-CSA powder could then be dissolved in appropriate solvent mixtures. For the data reviewed here, these powders were dissolved in m-cresol or chloroform or mixtures of these solvents. The resulting properties were shown to vary dramatically depending on which solvent was used through the effects of secondary doping [60-63,99]. The alternative way to obtain solutions of doped PAN-CSA is to separately add the EB powder into a volume of solvent and the HCSA into a volume of solvent and then mix the two solutions. 

Both the imine and the secondary amine nitrogens in polyaniline can be protonated by weak carboxylic acids of different pK values. Solid layers prepared from such doped polyanilines have different selectivity for interaction with gases. It is partially derived from the interaction of the analyte with the doping anion. 

Polyaniline solutions for fiber spinning were prepared using the secondary amines HPMI and 4-methylpiperidine (4-MP) as stabilizers for the concentrated EB/NMP solutions. These reduced the EB more slowly than secondary amines such as 2-methylaziridine [43]. Polyaniline fibers were processed from dope solutions in which the concentration of EB base powder (M 150,000 g/mol) varied from 17.5 to 25 wt% polyaniline in the case of the HPMI/NMP or 20 wt% of EB base powder (M 200,000 g/mol) for the 4-MP. The stoichiometric ratio between the HPMI molecules and the EB tetramer repeat unit required to stabilize the dope solution was 1.1 1 whereas the 4-MP EB tetramer ratio was 1.2 1. The EB was mechanically stirred into the secondary amine/NMP solution until a smooth, lump-free solution was obtained. 

M. S. Rahmanifar, M. F. Mousavi, M. Shamsipur, Effect of self-doped polyaniline on performance of secondary Zn-polyaniline battery, Journal of Tower Sources 2002,110, 229. 

Self-doped polyanilines are advantageous due to properties such as solubility, pH independence, redox activity and conductivity. These properties make them more promising in various applications such as energy conversion devices, sensors, electrochromic devices, etc. (see Chapter 1, section 1.6). Several studies have focused on the preparation of self-doped polyaniline nanostructures (i.e., nanoparticles, nanofibers, nanofilms, nanocomposites, etc.) and their applications. Buttry and Tor-resi et al. [51, 244, 245] prepared the nanocomposites from self-doped polyaniline, poly(N-propane sulfonic acid, aniline) and V2O5 for Li secondary battery cathodes. The self-doped polyaniline was used instead of conventional polyaniline to minimize the anion participation in the charge-discharge process and maximize the transport number of Li". In lithium batteries, it is desirable that only lithium cations intercalate into the cathode, because this leads to the use of small amounts of electrolyte... 

Polyanilines have been processed fi om solutions of neutral polyaniline in NMP, DMPU and others for some time[l,2]. Significant strides have been made in making fibers form these solutions. None eless, the technique suffers fi om the disadvantage that processed articles are non-conductive and need to be doped in a secondary step. The technique is not suited for preparation of coatings on a commercial scale. Processability of polyaniline in the doped form is more attractive as it removes the subsequent doping step. Functionalized protonic acids such as camphor sulfonic acid, preferably in the presence of m-cresol and dodecyl... 

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