Conductors poly

The molecular orbital (MO) calculations within the PM3 method, using a MOP AC package, provided an explanation of the advantages of a new redox system, poly(l,4-phenylene-l,2,4-dithiazolium-3, 5 -yl) (PPDTA), as a cathode material for high-capacity lithium secondary batteries in comparison with three typical polymer conductors (poly-/>-phenylene, polypyrrole, and polythiophene). The MO calculation revealed that the S-S bond in the 1,2,4-dithiazo-lium moiety of PPDTA caused gap narrowing and a downshift of HOMO and LUMO levels, which is consistent with the electrochemical experiment (HOMO = highest occupied molecular orbital LUMO = lowest unoccupied molecular orbital) <2001MI2305>. 

Figure 1.2 shows the chemical strnctnre of an organic conductor, poly(3,4-ethylene diocythiophene) poly(styrenesnlfonate) (PEDOT PSS), that is widely used for electrodes. Inorganic materials, like silver and other metals, often as filled pastes, are also used when higher conductivity is needed. 

A second type of soHd ionic conductors based around polyether compounds such as poly(ethylene oxide) [25322-68-3] (PEO) has been discovered (24) and characterized. These materials foUow equations 23—31 as opposed to the electronically conducting polyacetylene [26571-64-2] and polyaniline type materials. The polyethers can complex and stabilize lithium ions in organic media. They also dissolve salts such as LiClO to produce conducting soHd solutions. The use of these materials in rechargeable lithium batteries has been proposed (25). 

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(phenylenepyrazoles), 5, 300 Polypyrazoles, 5, 300 N-substituted, 5, 300 Polypyrazolines, 5, 300 Poly(pyrazol-l-yl) borates as ligands, 5, 225, 235 Polypyrroles applications, 4, 376 Polypyrrole tetrafluoroborate conductors, 1, 355 Polysaccharides as pharmaceuticals, 1, 152 Poly-2,5-selenienylenes applications, 4, 971 Polysilacyclopentanes, 1, 609 Polysufides macrocyclic... 

The polymers which have stimulated the greatest interest are the polyacetylenes, poly-p-phenylene, poly(p-phenylene sulphide), polypyrrole and poly-1,6-heptadiyne. The mechanisms by which they function are not fully understood, and the materials available to date are still inferior, in terms of conductivity, to most metal conductors. If, however, the differences in density are taken into account, the polymers become comparable with some of the moderately conductive metals. Unfortunately, most of these polymers also have other disadvantages such as improcessability, poor mechanical strength, instability of the doped materials, sensitivity to oxygen, poor storage stability leading to a loss in conductivity, and poor stability in the presence of electrolytes. Whilst many industrial companies have been active in their development (including Allied, BSASF, IBM and Rohm and Haas,) they have to date remained as developmental products. For a further discussion see Chapter 31. 

Since the realization in the early 1980s that poly (ethylene oxide) could serve as a lithium-ion conductor in lithium batteries, there has been continued interest in polymer electrolyte batteries. Conceptually, the electrolyte layer could be made very thin (5im ) and so provide higher energy density. Fauteux et al. [31] have recently reviewed the present state of polymer elec-... 

Here we introduce a personal point of view about the interactions between conducting polymers and electrochemistry their synthesis, electrochemical properties, and electrochemical applications. Conducting polymers are new materials that were developed in the late 1970s as intrinsically electronic conductors at the molecular level. Ideal monodimensional chains of poly acetylene, polypyrrole, polythiophene, etc. can be seen in Fig. 1. One of the most fascinating aspects of these polymeric... 

Abstract In this paper the synthesis, properties and applications of poly(organophos-phazenes) have been highlighted. Five different classes of macromolecules have been described, i.e. phosphazene fluoroelastomers, aryloxy-substituted polymeric flame-retardants, alkoxy-substituted phosphazene electric conductors, biomaterials and photo-inert and/or photo-active phosphazene derivatives. Perspectives of future developments in this field are briefly discussed. 

Polyphosphazenes sulfonates XIX with the anion covalently attached to the polymer are a new class of cation conductors that have been synthesized by Shriver [625]. They were obtained by reaction of Na0C2H4S03Na with an excess of polydichlorophosphazene in the presence of 15-crown-5, followed by the reaction of the partially substituted product with the sodium salt of poly(ethylene glycol methyl ether). The conductivity at 80 °C of the polymer with x=1.8, m=7.22 is 1.7x10 S cm This low conductivity can be attributed to an extensive ion pair formation between the sodium and sulfonate ions. 

We report here studies on a polymer fi1m which is formed by the thermal polymerization of a monomeric complex tris(5,5 -bis[(3-acrylvl-l-propoxy)carbonyll-2,2 -bipyridine)ruthenium(11) as its tosylate salt,I (4). Polymer films formed from I (poly-I) are insoluble in all solvents tested and possess extremely good chemical and electrochemical stability. Depending on the formal oxidation state of the ruthenium sites in poly-I the material can either act as a redox conductor or as an electronic (ohmic) conductor having a specific conductivity which is semiconductorlike in magnitude. 

The use of organic polymers as conductors and semiconductors in the electronics industry has led to a huge research effort in poly(thiophenes), with a focus on the modification of their electronic properties so that they can behave as both hole and electron conductors. Casado and co-workers [60] have performed combined experimental and theoretical research using Raman spectroscopy on a variety of fluorinated molecules based on oligomers of thiophene, an example of one is shown in Figure 7. 

Lithium iodide is the electrolyte in a number of specialist batteries, especially in implanted cardiac pacemakers. In this battery the anode is made of lithium metal. A conducting polymer of iodine and poly-2-vinyl pyridine (P2VP) is employed as cathode because iodine itself is not a good enough electronic conductor (Fig. 2.3a). The cell is fabricated by placing the Li anode in contact with the polyvinyl pyridine-iodine polymer. The lithium, being a reactive metal, immediately combines with the iodine in the polymer to form a thin layer of lithium iodide, Lil, which acts as the electrolyte ... 

Recently, several molecule-based microelectrochemical devices have been developed by the Wrighton group.(14.15.21-22) A microelectrode array coated with poly(I) results in a microelectrochemical transistor with the unique characteristic that shows "turn on" in two gate potential, Vq, regimes, one associated with the polythiophene switching from an insulator to a conductor upon oxidation and one associated with the v2+ + conventional redox centers. 

Schuster, M., Kreuer, K. D., Anderson, H. T. and Maier, J. 2007. Sulfonated poly(phenylene sulfone) polymers as hydrolytically and thermooxidatively stable proton conductors. Macromolecules 40 598-607. 

Polymer electrolytes (e.g., poly (ethylene oxide), poly(propylene oxide)) have attracted considerable attention for batteries in recent years. These polymers form complexes with a variety of alkali metal salts to produce ionic conductors that serve as solid electrolytes. Their use in batteries is still limited due to poor electrode/electrolyte interface and poor room temperature ionic conductivity. Because of the rigid structure, they can also serve as the separator. Polymer electrolytes are discussed briefly in section 6.2. 

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