Poly electrical conductivity

When the process medium is electrically conductive (dielectric values > 10), the capacitor developed above does not work the iasulatiag material needed between the two conductive plates is lost. The conductive Hquid surrounding the probe acts as a short circuit to the tank wall (second plate of the capacitor). To reestabUsh the dielectric (iasulatiag material), the probe can be iasulated with a nonconductive material such as tetrafluoroethylene (TFE), poly(vinyhdene fluoride) (PVDF), poly(vinyl chloride) (PVC), etc. The capacitor exists between the probe rod, through the thickness of the iasulation (dielectric), to the conductive Hquid which is now acting as the second plate of the capacitor, or ground reference (Fig. 9). 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Some polymers from styrene derivatives seem to meet specific market demands and to have the potential to become commercially significant materials. For example, monomeric chlorostyrene is useful in glass-reinforced polyester recipes because it polymerizes several times as fast as styrene (61). Poly(sodium styrenesulfonate) [9003-59-2] a versatile water-soluble polymer, is used in water-poUution control and as a general flocculant (see Water, INDUSTRIAL WATER TREATMENT FLOCCULATING AGENTs) (63,64). Poly(vinylhenzyl ammonium chloride) [70304-37-9] h.a.s been useful as an electroconductive resin (see Electrically conductive polya rs) (65). 

Common conductive polymers are poly acetylene, polyphenylene, poly-(phenylene sulfide), polypyrrole, and polyvinylcarba2ole (123) (see Electrically conductive polymers). A static-dissipative polymer based on a polyether copolymer has been aimounced (124). In general, electroconductive polymers have proven to be expensive and difficult to process. In most cases they are blended with another polymer to improve the processibiUty. Conductive polymers have met with limited commercial success. 

Although polyacetylene has served as an excellent prototype for understanding the chemistry and physics of electrical conductivity in organic polymers, its instabiUty in both the neutral and doped forms precludes any useful appHcation. In contrast to poly acetylene, both polyaniline and polypyrrole are significantly more stable as electrical conductors. When addressing polymer stabiUty it is necessary to know the environmental conditions to which it will be exposed these conditions can vary quite widely. For example, many of the electrode appHcations require long-term chemical and electrochemical stabihty at room temperature while the polymer is immersed in electrolyte. Aerospace appHcations, on the other hand, can have quite severe stabiHty restrictions with testing carried out at elevated temperatures and humidities. 

Poly-1,2-1//-azepines, produced by gas-phase photopolymerization of aryl azides yield, after oxidation, electrically conducting films.103 By photolyzing 4-(pcntyloxy)phenyl azide in the gas phase, a flexible polyazepine is produced which can be deposited directly as a thin polymer film onto a suitable surface. 

The microstructure and architecture of polymers can also gready influence die properties of die polymers. For example, poly(3-substituted thiophene)s could have three microstructure joints s-trans (head to tail), s-trans (head to head), and s-cis (head to tail) (Fig. 9.3). The regioregular head-to-tail poly(3-substituted thiophene)s exhibit higher electrical conductivity values and higher... 

Most conducting polymers, such as doped poly(acetylene), poly(p-pheny-lene), and poly(/ -phenylene sulfide), are not stable in air. Their electrical conductivity degrades rapidly, apparently due to reaction with oxygen and/or water. Poly(pyrrole) by contrast appears to be stable in the doped conductive state. 

Table 5.3 Examples of electronically conducting polymers, y is the level of electrochemical doping and k is the maximum electrical conductivity. Except for poly acetylene and polyparaphenylene, only p-doping is considered... 

In this paper we describe the preparation of thin polymer films by surface catalysis and anodic deposition. The results indicate that both synthesis routes produce orientationally ordered films that have similar infrared spectra. It is also shown that thin ordered films of poly(thiophene) have different electrochemical behavior than the fibrous films that are electrically conducting. 

T. Yamamoto, Electrically conducting and thermally stable TT-conjugated poly(arylene)s prepared by organometallic processes, Prog. Polym. Sci., 17 1153-1205, 1992. 

Y. Yamamoto, K. Sanechika, and A. Yamamoto, Preparation of thermostable and electric-conducting poly(2,5-thienylene), J. Polym. Sci., Polym. Lett. Ed., 18 9-12, 1980. 

R.D. McCullough and R.D. Lowe, Enhanced electrical conductivity in regioselectively synthesized poly(3-alkylthiophenes), J. Chem. Soc., Chem. Commun. 70-72, 1992. 

T. Yamamoto, T. Murauyama, Z.-H. Zhou, T. Ito, T. Fukuda, Y. Yoneda, F. Begum, T. Ikeda, S. Sasaki, H. Takezoe, A. Fukuda, and K. Kubota, -ir-Conjugated poly(pyridine-2,5-diyl), poly(2,2 -bipyridine-5,5 -diyl), and their alkyl derivatives. Preparation, linear structure, function as a ligand to form their transition metal complexes, catalytic reactions, //-type electrically conducting properties, optical properties, and alignment on substrates, J. Am. Chem. Soc., 116 4832-4845,... 

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