POLY PYRROLE P Py

along with P(ANi), represents the CP most commonly investigated for commercially practical secondary batteries. Li/P(Py) Queries exhibit good discharge characteristics and cyclability, as Table 15-1 reveals. Typical discharge and charge reactions for a standard, Li/LiC104-liquid or solid electrolyte/P(Py) battery, are very similar to those cited for P(Ac) above. We may now briefly discuss illustrative, individual examples of P(Py) batteries and improvements therein. 

Nishizawa et al. [708] studied Li secondary batteries based on cathodes comprised of P(Py)-coated spinel LiMn204 nanotubules of ca. 200 nm outer diameter, prepared by thermal decomposition of an aqueous solution containing Li and Mn nitrates using a nanoporous alumina membrane as a template which was later dissolved off. These electrodes showed superior performance to P(Py)-coated LiMu204 thin films, with capacities claimed to be up to 12 times greater. 

Along with P(Py), P(ANi) is a CP most studied for battery applications, and the only one, to date, which has been successfully commercialized, as detailed further below. The uniqueness of P(ANi) is, of course, the diffusion of protons, rather than more bulky ions, as the counterions, and the fact that doping levels as high as 50% are attainable. Several examples of and improvements in P(ANi) batteries may now be cited. 

Among CPs, P(ANi) appears to yield the best-performing batteries, in terms of such parameters as spontaneous discharge (de-doping, which retards shelf-life), coulombic efficiency and cyclability. Thus, e.g., a typical Li/LiC104-PC/P(ANi) battery using 

Oyama et al. [719, 720] described a novel CP cathode made by mixing chemically polymerized P(ANi) with 2,5-dimercapto-l,3,4-tliiadiazole (DMcT) in A/-Me-2-pyrrolidinone solvent, and spreading and drying the resulting dark, viscous ink on a carbon film to obtain die active cathode. This cathode functioned as a Li ion reservoir, much in the tradition of the Li-intercalate composite electrodes and showed the following reactions  

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Fig. 1-2 Schematic illustration of monomer unit (left) and CP (right) for three (over) common CPs a) Poly(aniline) (P(ANi)) b) Poly(pyrrole) (P(Py)) and c) Poly (thiophenes).

Fig. 2-15 Band structure evolution for Poly(pyrrole) (P(Py)). The evolution from (a) to (d) is with progressively increasing doping.

Fig. 2-17 Density of States (DOS) band structure of Poly(pyrrole) (P(Py)). After Ref. [450]. Reproduced with permission.

The simplest spectroelectrochemical measurement which yields information on electrochromic properties of CPs is the UV-Vis-NIR spectroelectrochemical curve, an in-situ or sometimes ex-situ measurement of the transmission-mode UV-Vis-NIR spectrum of the CP at various applied potentials. Such a measurement, which we shall hereinafter abbreviate as a SPEL curve (or just SPEL), is depicted in Fig. 3-1 this figure is a re-representation of the optical spectra of poly(pyrrole) (P(Py)) discussed in Chapter 2, with an abscissa in terms of wavelength, and represents a particularly well-behaved CP system. To recap again here, the single, prominent valence conduction (tt tt ) band transition in the pristine polymer (at ca. 388 nm) is accompanied by three additional polaron based transitions at low doping level (ca. 590 nm, 885 nm, 1,771 nm), which finally evolve into two bipolaron based bands (ca. 459 nm, 1,240 nm). 

CPs have been investigated for a very wide variety of battery applications, although mostly for secondary (rechargeable) batteries. They have been used as the anode as well as the cathode material, although cathode materials in Li secondary batteries have overwhelmingly been the main focus of interest. Applications have included all-CP (anode/cathode) batteries [685], lead-acid batteries [686], Zn batteries [687] and others. Although poly(aniline) (P(ANi)) and poly(pyrrole) (P(Py)) have overwhelmingly been the primary focus of interest, other common CPs studied have included poly(p-phenylene) (P(PP)), poly (acetylene) (P(Ac)), poly (thiophene) (P(T)). 

In the CP literature and among workers in the field, the monomers are generally represented by abbreviations, e.g. ANi for aniline, and the polymer also abbreviated in short-hand notation, following the custom in other polymer literature. For example, P(ANi) and PANi may be used to represent poly (aniline), P(Py) and PPy poly (pyrrole), and P(3MT), P3MT or PMT may be used to represent poly (3-methyl-thiophene). 

Biswas and Roy [126] also studied the thermal stability characteristics (Table 16.7) of chemically prepared pyrrole (PY) modified poly-N-vinylcarbazole (NVC) composite P(PY-NVC) and reported the percentage weight losses for PPY, PNVC and P(PY-NVC) during thermal degradation. It was observed that the thermal stability of P(PY-NVC) was intermediate between those of individual components. 50% weight loss was recorded at 400°C in the case of PPY, at 450°C for PNVC and at 425°C for P(PY-NVC) respectively. They inferred that the thermo-oxidative breakdown of aromatic linkages of the polymer matrix occurs in the temperature range of 300-550°C in case of P(PY-NVC)... 

Phenol, catechol, p-cresol Poly(N-3- aminopropyl pyrrole-co-Py) Tyrosinase Formation of imide bonds onto pre-formed polymer coating [167]... 

Ihble VI. Thermal Stabilities" of Polypyrrole (PPY) Poly(AT-vinylcarbazole) (PNVC), and Poly(pyrrole-19-vinylcarbazole) P(PY-NVC)... 

What happens if one introduces substituted analogs of the pyrrole monomer unit, e.g. N-methyl pyrrole in place of pyrrole This is seen in Fig. 4-8 the voltammetric behavior of the substituted analogs is very similar to that of P(Py), but with an anodic shift of the redox peak potentials. This is explained by the likely participation of protons in the facilitation of the redox of P(Py), which is not possible in N-substituted analogs. Another effect of N-substitution in poly(pyrroles) is of course increased environmental stability, as oxidants invariably first attack the exposed, electron rich N-atom of unsubstituted pyrrole. That monomer structure can sometimes directly influence polymer behavior is also seen in the plot of oxidation potentials of monomer vs. polymer for poly(thiophene) analogs in Fig. 4-9 here the two oxidation potentials exactly parallel each other, i.e. a monomer more difficult to oxidize implies a polymer also more difficult to oxidize. On the other hand, alkoxy-substituted P(ANi) show voltammetric behavior very close to that of the unsubstituted P(ANi), with peaks shifted less than 90 mV anodically (Fig. 4-10). 

In a precursor-polymer synthetic approach [288], amphiphiles which formed charged complexes with precursor polymers of poly(p-phenylene vinylene) (P(PV)) and poly(thienylene vinylene) (P(TV)) were spread onto solutions of these precursor polymers. This unique complex is then transferred to an appropriate substrate using standard LB techniques, and then converted to P(PV) or P(TV) via heat treatment. In a similar but rather novel, in-situ polymerization approach from the Rubner group [289], LB films of ferric stearate are exposed sequentially to HCl vapor (generating FeCls oxidant) and pyrrole monomer, yielding conductive LB P(Py) films. 

An oxidant-sorption procedure was used by Ojio and Miyata [338] for the fabrication of P(Py)/PVA (Poly(Vinyl Alcohol)) composites. PVA, of M 22,000, was dissolved with FeClj (the oxidant) in water, a film cast from this solution onto a PET film substrate. This oxidant-saturated host-polymer film was then exposed, in a desiccator at low temperature and in a deoxygenated atmosphere, to monomer (pyrrole) and water vapor for 0.5 to 24 h, with the resulting composite films, ca. 2 jam thick, dried in vacuum. Conductivities and transmission values saturated at about 1 h exposure time, to ca. 1 S/cm and 40% ( 550 nm) for a 70 30 w/w ratio PVA/FeClj. Transmission of the film was down to ca. 55% within 0.5 h, (with conductivity ca. 0.1 S/cm) for the same PVA/FeClj ratio. Higher PVA/FeClj ratios (90 10, 95 5) gave not only higher transmissions with minimal conductivity reduction, but also more homogeneous films as evidenced by SEM. 

A similar procedure, using highly viscous liquid complexes formed by FeClj (oxidant) with polymers such as poly(ethylene oxide) (PEO), poly(j3-propiolactone) (PPL) and poly(l,5-di-oxepan-2-one) (PDXO) was employed by Rabek et al [339] to fabricate P(Py) composites. The complexes were first prepared in dry nitro-methane (polymer FeClj ratio 7 3) and cast as films on glass. The films were then exposed to pyrrole vapor in a desiccator, yielding composites of 50 - 200 pm thickness over different reaction times. Excess oxidant and unreacted monomer were removed with a nitromethane wash. Conductivities were ca. 10 S/cm and transmissions below 50% in the mid-Visible region. 

Wiersma et al. [284] described a method for preparation of P(Py) or P(ANi) + polyurethane dispersions which may be applied to textile fibers. Aqueous solutions of pyrrole (or anilinium sulfate) and Fe(N03)3 are added to a dispersion of polyurethane in water. After 20 hrs reaction time, a P(Py) (or P(ANi)) poly-(urethane) dispersion is obtained, which can then be used to fabricate coatings with claimed conductivities up to 10 S/cm. 

For each class outlined in problem 1, briefly discuss the difference in all possible properties you can enunciate between the parent polymer and common derivatives (e.g. poly(N-alkyl pyrrole) vs. P(Py), poly(o-methoxy aniline) vs. P(ANi)). 

Pyo and Reynolds [1028] studied the controlled release of ATP from P(Py) films. They again used the common approach for incorporating the ATP into the CP, viz. electropolymerizing from aqueous solutions of 0.1 M pyrrole and 20 mM Disodium ATP. They however used a unique, bilayer approach to minimize problems with spontaneous (i.e. open circuit) release of die ATP from the CP into solution. In this bilayer approach, the outer CP film in contact with solution was separated from the metal electrode substrate by a layer of reduced, insulating CP film. As the inner, insulating layer, P(Py)/poly(styrene sulfonate) (PSS) re-doped with ATP was used, while poly(A -Me-Py) was used as the outer film. The authors claimed that this allowed more controlled electrochemical release of ATP from the inner film. 

Figure 5.20 Synthetic route for PSSA-g-PPY. PY = pyrrole, CMS = chloromethyl-styrene, PMS = pyrrolyknethylstyrene, SSNa = sodium styrenesulfonate, P(SSNa-co-PMS) = poly(sodium styrenesulfonate-co-pyrrolylmethylstyrene). (Reprinted with permission from Macromolecules, 38, 1044. Copyright (2005) American Chemical Society.)...

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