Polypyrrole structures

The base unit of polypyrrole is pyrrole, the structure of which is a five member hetero-aromatic ring containing a nitrogen atom, as shown in Fig. 13a. Polypyrrole is synthesized from the pyrrole monomer by mild oxidation, using chemical or electrochemical technique. After the oxidation of the monomer, a black solid polymer is precipitated from the solution. The polypyrrole structure in its oxidized form is shown in Fig. 13b. Film thicknesses on the order of 1-1.5 pm, using in situ deposition, were obtained for our application [19]. 

Fig. 13 (a) Polypyrrole structure and (b) Polypyrrole structure in its oxidized form... 

To enhance the response of the polypyrrole sensor towards DMMP, acid dopants were added to the polypyrrole structure. The rational for doping polypyrrole was to introduce secondary doping sites for DMMP in the structure. Secondary doping... 

Duchet, J., R. Legras, and S. Demoustier-Champagne. 1998. Chemical synthesis of polypyrrole Structure-properties relationship. Synth Met 98 113. 

The heat-treated M/N/C composite materials, such as CoPPy/C, can also be considered as multifunctional catalysts, featuring Co nanoparticles coated with Co oxides and Co " species associated with N-C moieties that originate from the polypyrrole structures [82]. An illustration of the CoPPy/C catalyst surface and the ORR processes is shown in Fig. 15.30. The Co-N type site (shown as a C0-N4 complex) supports the initial adsorption of the O2 molecule and conversion of O2 to the intermediate reaction prcxluct, H02, by a 2e reduction reacticm. The H02 species can further react at a decorating Cof)y/Co nanopaiticle phase. Chu et al. [126] found that the mixture of the heat-treated Co- and Fe-tetraphenylporphyrins (CoTPP/FeTPP) had better catalytic performance for ORRs in acid media than that of the respective heat-treated single components. All of the above cited research results point to the fact that carefully designed bifuncticmal or multifunctional catalysts can be much more active for ORR than their single components. 

A general problem in the synthesis of those composites is the appearance of conductivity gradients in their thickness direction, which are caused by inhomogeneities in the polypyrrole structure, as a result of difficulties in diffusion of the electrolyte across the host polymer. A method for overcoming these problems has been developed by Wang et al. [375]. PPy/PVC composites can significantly improve uniformity in electrical conductivity and resistance to mechanical delamination when a certain amount of electrolyte is mixed with PVC prior to the electrochemical reaction. After electropolymerization of pyrrole in the presence of electrolyte blended PVC for 20 minutes, the conductivity across the film thickness showed more than ten orders of magnitude difference with respect to film obtained from unblended PVC. 

Another factor which limits our success in correlating polypyrrole structure with 0.02 lm Anotec morphology is that we have yet to obtain a reliable complete cross-sectional profile of the membrane. However, we are currently pursuing further high resolution studies of both y-alumina membranes and extended electropolymerizations to better understand this aspect of the work. 

It has proven possible to add a wide range of additional functionalities to the parent polypyrrole structure, opening up an exciting array of pofential applications for fhese maferials. Two distincf approaches fo achieving this additional functionality have been successfully employed, namely ... 

FIGURE 4-13 Structures of common polymeric coatings (a) Nafion, (b) polyvinyllferro-cene (c) polyvinylpyridine id) polypyrrole. 

Figure 38. Evolution of the proposed surface aspect of a polypyrrole film during an oxidation reaction initiated from high cathodic potentials (E < -800 mV vs. SCE). The chronoamperometric response is shown at the bottom. Experimental confirmation can be seen in the pictures in Ref. 177. (Reprinted from T. F. Otero and E. Angulo, Oxidation-reduction of polypyrrole films. Kinetics, structural model, and applications. Solid State Ionics 63-64, 803, 1993, Figs. 1-3. Copyright 1993. Reprinted with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055, KV Amsterdam, The Netherlands.)...

The diversity of conducting polymers is best illustrated by Krivoshei and Skorobogatov s book,15 although many more examples have since been reported. The most widely studied classes, from an electrochemical point of view, are the polypyrroles, polythiophenes, and polyanilines21 22 (Structures 2-4), and these are the focus of this chapter. A wide... 

Figure 15. Complex plane impedance plots for polypyrrole at (A) 0.1, (B) -0.1, (C) -0.2, (D) -0.3, and (E) -0.4 V vs. Ag/AgCl in NaCl04(aq). The circled points are for a bare Pt electrode. Frequencies of selected points are marked in hertz. (Reprinted from X. Ren and P. O. Pickup, Impedance measurements of ionic conductivity as a probe of structure in electrochemi-cally deposited polypyrrole films, / Electmanal Chem. 396, 359-364, 1995, with kind permission from Elsevier Sciences S.A.)...

Cross-linked structure of polypyrrole, 311 Cross-linking, 330... 

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

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