Structures of polypyrrole

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

Figure 6. Band structure of polypyrrole as a function of doping level (schematic). (A), neutral polymer (B) polaron (+), spin = 1/2, 3 new transitions (C) bipolaron (++), spin = 0, 2 transitions (D) Heavily doped, bipolaron bands.

Polypyrrole and polythienylene (Fig. 16) have the same number of tt electrons as poly(p-phenylene). The electronic structure of polypyrrole has been examined by several authors (Ford et al., 1982 Br6das et al., 1983a). The HO and the LU bands are of tt nature. The orbital pattern of the HOMO accompanied by the top of the valence band has no contribu-... 

The structure of polypyrrole in the solid state has been studied by means of high resolution solid-state NMR spectroscopy [12]. However, the structure is insufficiently analyzed because of the complexity of the unresol-vable broad aromatic signal. This is because there are several magnetically non-equivalent aromatic carbons as shown in Fig. 16.5. 

The Structure of polypyrrole, prepared electrochemically, has been analyzed by using high resolution solid-state NMR spectroscopy. The... 

M. Area, Ph.D. Thesis, Investigation of the Structure of Polypyrrole by Electrochemical and Spectroscopic Techniques, and the Effect of Gamma Rays on Polypyrrole, Hacettepe University, Ankara, Turkey, 1986,... 

R. McNeill, R. Siudak, J. Wardlaw, D. Weiss, Electronic Conduction in Polymers. I. The Chemical Structure of Polypyrrole. Aust. J. Chem. 1963,16, 1056. 

FIGURE 16.7 Cross-linked structure of polypyrrole. (From Otero, T.F., Modern Aspects of Electrochemistry, Kluwer Academic, New York, 1999. With permission.)... 

Bredas, J. L., Themans, B., and Andre, J. M., Valence effective Hamiltonian technique for nitrogen-containing polymers electronic structure of polypyrrole, pyrolized polyacrylonitrile and derivates, Phys. Rev. B, 27, 7827-7842 (1983). 

The intercalation of dopants to conducting polymer chains leads to an increase in volume of up to 30 % [8], This property is used in actuators (polymer-based artificial muscles). Bilayer structure of polypyrrole-based anode and cathode is a simple model. At anode, p-doping of polymer occurs to swell, while the other side shrinks because of the expulsion of counterions. This volume changes promote a bend of the layers. The change of poles cancels the volume changes and gives rise to the movement in the opposite direction. 

To separate the y-alumina without destroying the polypyrrole, screening experiments were performed to discover the optimum level of exposure to sodium hydroxide leachant. From the Anotec literature it is evident that y-alumina dissolves readily in NaOH, but it is also known that conductivities and structure of polypyrrole are affected by exposure to bases. 

Maw S, Smela E, Yoshida K, Stein RB (2005) Effects of monomer and electrolyte concentrations on actuation of PPy(DBS) bilayers. Synth Met 155 18-26 Melling D, Wilson SA, Beiggren M, Jager EWH (2011) Altering the structure of polypyrrole and the influence on electrodynamic performance. In Proceedings of SPIE - The International Society for Optical Engineering, vol 7976... 

Four peaks (a, P, y and 8) are assigned to the oxidised strnctnre, the aromatic form, the quinoid form, and the 2,3-bond structure, of polypyrrole, respectively. The half-width of peak y is a measure of electrical conductivity. Electrical conductivity measurements at room temperature and -23 °C show that the hopping conduction mechanism is the dominant one for polypyrrole. 

In the following, three examples of conductive polymers will be discussed because these are the most commonly used in biosensors. Table 17.1 shows the chemical structures of polypyrrole, polyaniUne and PEDOT, the three conductive polymers reviewed in this section. 

Table 17.1 Chemical structure of polypyrrole, PEDOT, polyaniline...

The polymerization conditions used to prepare polypyrrole not only determine the polymer composition, but also influence the structure of the polymer from the molecular level to the microscopic level. In this section, the studies characterizing the detailed structure of polypyrrole films, coatings, particles and colloidal dispersions are reviewed. These studies provide the foundation for understanding the properties of polypyrroles, as described in Chapter 3. 

The most readily observed structure of polypyrrole samples is the peculiar surface morphology common to all electropolymerized PPy films and coatings. The morphology consists of nodules ranging in size to hundreds of microns that, themselves, consist of aggregations of smaller particles. The structure has been referred fo as a "cauliflower-" or "fractal-like" surface. 

The electrode material has also been found to influence the surface morphology of electrochemically prepared polypyrrole films. In our own work, we used transmission electron microscopy (TEM) to investigate the cross-sectional structure of polypyrrole films prepared on different substrates. In all cases, the large surface globules were observed to be the caps of cone-shaped structures that extended to the electrode surface of the polypyrrole film (see Chapter 3). Interestingly, Yoon et al. showed that the cauliflower-type surface morphology could be virtually eliminated by carefully polishing the electrode surface. ... 

Figure 1. Structure of polypyrrole. High conductivity may be induced by negative ion doping to create positive defects on the polymer backbone.

It is surprising that the electrical conductivity can be obtained as high as 10 S/cm with only 5 wt.% of pyrrole monomer being incorporated, while the incorporation of 40 wt.% of pyrrole leads to 0.01 S/cm in the solution polymerization (Fig.2). The network structure of Polypyrrole is maintained even when the ratio of pyrrole monomer is decreased. Therefore, a network structure of polypyrrole can be obtained with only 5 wt.% of pyrrole and this brings about the highest conductivity. 

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