Modification polypyrrole

Co-polypyrrole complex polypyrrole modification, deposited on carbon [13]... 

Figure 6.29 shows, as an example, the effect of surface modification on the sta-bihty of sihcon electrode in an aqueous solution. The bare sihcon surface is quickly passivated in aqueous solution under illumination. Coating the electrode with a layer of either ferrocene or polypyrrole gives an improvement in the stabihty. The stability is further improved by a two-layer coating of ferrocene/polypyrrole as shown in Fig. 6.29. 

Cyclic voltammetries (CVs) of CNTs A/CoSi700 modified by electrodepos-ited polypyrrole present the characteristic boxlike shape of an ideal capacitor even at moderate scan rates of 2 mV/sec, as shown in Figure 7.13 (Frackowiak and Beguin, 2002). Values of specific capacitance of nanotubes are significantly enhanced after modifications such as electrodeposition of a thin layer of conducting polymers, because of the contribution of pseudofaradaic properties of the polymer. 

Studies of the chemical properties of polythiophenes have been limited. As with polypyrroles, a hydrophobic backbone is formed, and the polymer has ion-exchange properties. Modification of chemical properties by incorporation of appropriate counterions is not so readily addressable because polymerization must be carried out from nonaqueous solution and occurs at more anodic potentials compared to pyrrole. 

More recently, a polypyrrole-modified s-BLM has been found to be sensitive to hydrogen ions [80]. Concerning pH probes, they could be the basis for monitoring blood gases (oxygen, carbon dioxide) and related variables (pH, Na" ", K" ", Ca " ", Cl ) as well as metabolites (glucose, urea, lactate, creatinine) after suitable modification. It is envisioned that all these could be monitored simultaneously and/or sequentially in a small sample of undiluted whole blood or in plasma [78]. 

Thin films of conductive polymers like polypyrrole, polyaniline, etc are also used for the surface modification of the semiconductor electrodes [26, 27]. Their performance mechanism has not yet been deciphered. Most likely, the coating is a combination of a protective film and the charge carrier, the more so that reversible redox couples are used to be introduced into films [28], as well as catalytically-active admixtures like Ru02 [29]. Such films were used to stabilize a promising "solar" electrode material, amorphous silicon [30]. 

Biswas and Roy [118,119] studied the degradation and stability of chemically prepared polypyrrole substituted by phthalic anhydride (PPY-PhAn) and pyromellitic dianhydride (PPY-PMDA) by using a thermal analyser and IR spectroscopy. They found that the chemical modification enhanced the thermal stability of the modified polypyrrole as compared with... 

Interest in porphyrin synthesis continues unabated. The first examples of a truly stepwise procedure, in which four pynole residues are linked together one by one, have now been described (see Section 7). Methods such as this are particularly useful for the preparation of isotopically labeled compounds for biosynthetic studies, where it is of considerable advantage both experimentally and economically to introduce the label as late as possible in the synthetic sequence. It is still, however, often necessary to carry out modification of side chains, or introduce labels, at the porphyrin stage because of the lability of the desired side chains under the conditions required to construct the polypyrrolic precursors and to cyclize them to porphyrins. 

M. Ulmann, R. Kostecki, J. Augustynski, D.J. Strike, and M. Koudelka-Hep, Modification des polymers conducteurs avec de petites particules metalliques proprietes des films de polypyrrole et de polyaniline platines, Chimia, 46, 138-140 (1992). 

Maria Omastova and Ivan Chodak prepared conductive polypropylene/ polypyrrole composites using the method of chemically initiated oxidative modification of polypropylene particles in suspension by pyrrole. In order to prepare the composite, polypropylene particles were dispersed in water-methanol mixture and FeCb was added to be used for chemical oxidation. Addition of pyrrole started formation of polypyrrole particles in polypropylene suspension. The electrical and rheological properties of the composite were compared with polypropylene/polypyrrole composite prepared by melt mixing of pure polypropylene with chemically synthesized polypyrrole and with polypropylene/carbon black composites also prepared by melt mixing. Elemental analysis verified presence of polypyrrole in polypropylene matrix. The conductivity studies show that even a very small PPy amount present in composites results in a significant increase in... 

In in-situ polymerization, nanoscale particles are dispersed in the monomer or monomer solution, and the resulting mixture is polymerized by standard polymerization methods. This method provides the opportunity to graft the polymer onto the particle surface. Many different types of nanocomposites have been processed by in-situ polymerization. Some examples for in-situ polymerization are polypyrrole nanoparticle/amphiphilic elastomer composites magnetite coated multi-walled carbon nanotube/polypyrrole nanocomposites and polypyrrole/ silver nanocomposites. The key to in-situ polymerization is appropriate dispersion of the filler in the monomer. This often requires modification of the particle surface because, although dispersion is easier in a liquid than in a viscous melt, the settling process is also more rapid. 

For many conducting polymers including polyaniline, polypyrrole, and polythiophene, a rich chemistry of structural modifications has been developed making them potentially attractive materials for sensor applications [45,77-81]. Since, conjugated polymers respond to vapors at room temperature and can be deposited on a wide variety of substrates, they could be used in applications that prove to be difficult for traditional semiconductor gas sensors which often require high-temperature operation. 

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