Stability of Electrically Conducting Polymers

Polymers undergo chemical reactions just like any typical low molecular weight organic compound, leading to the deterioration of useful polymer properties. The ability of a polymer to retain its useful properties is defined as the stability. There are many external factors that a polymer has to withstand to retain its usefulness, such as heat, light, oxygen, ozone, moisture, mechanical stress, and 

INTRINSIC STABILITY OF ECPs r, UNDOPED ECPs DOPED ECPs  

COMPENSATION OR ELECTRICAL NEUTRALIZATION REACTIONS OF DOPED ECPs  

Tkble I. Dissociation Energies of Bonds Typically Present in Polymers 

Source Adapted with permission from R. W. Dyson, Ed., Specialty Polymers, 2nd ed., p. 13. Copyright 1998, Blackie Academic Professional, London. 

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Fig. 2. Important factors in the study of stability and stabilization of electrically conducting polymers.

Chapter 8. Stability of Electrically Conducting Polymers F. Mohammad... 

Lindfors, T. 2009. Light sensitivity and potential stability of electrically conducting polymers commonly used in solid contact ion-selective electrodes. J. Solid State Electrochem. 13 77-89. 

Development of electrically conducting polymers that can be processed as thermoplastics and possess the advantageous mechanical behavior and corrosion stability of plastics would open up entirely new fields of applications. Some of the many applications in which electrically conducting polymers would find a large market are cables and conducting electricity, wall papers that allow electrical heating, materials for antistatic equipment, and conducting fabrics. 

Blending of electrically conducting polymers with other more stable polymers may lead to better stability. 

Tkkeoka et al. [208] investigated in great detail the effect of several antioxidants as well as the effect of various doping acids on the stability of electrical conductivity of electrochemically prepared polypyrrole. The electrical conductivity (EC) of polypyrrole already had been observed to increases initially and then, after a maximum value, decrease on heating. The increase in EC may be attributed either to annealing of the polymer or to the semicon-... 

A major draw-back to the use of ECPs as conductive fillers is the instability associated with many of the key properties of these polymers. A number of electrically conducting polymers, such as polyacetylene, are unstable in air over long periods. Thermal stability can be problematical in some ECPs, and would therefore render these polymers unsuitable for use in hot environments. 

The most widely discussed application of electrically conductive polymers, that can be switched reversibly between two redox states, is their use for the storage of electrical energy in rechargeable batteries. Initial enthusiasm based on optimistic ideas has been quenched by several not fully solvable circumstances such as self-discharge and unsufficient cycle stability [12,13]. A loss of 10% in 1000 cycles for instance is an admirable scientific result, but death for a technical application. 

Electrically conducting polymer particles such as polypyrrole and polyaniline could also be prepared by dispersion polymerization in aqueous ethanol (31). The oxidation polymerization of pyrrole and aniline has been carried out at the electrode surfaces so far and formed a thin film of conducting polymer. On the other hand, polypyrrole precipitates as particles when an oxidizing reagent is added to a pyrrole dissolved ethanol solution, which contains a water-soluble stabilizer. In this way electrically conducting polymer particles are obtained and, in order to add more function to them, incorporation of functional groups, such as aldehyde to the surface, and silicone treatment were invented (32). 

A remarkable feature of phosphazene polymers of types tlj and (2) is that appropriate substituents (which are readily attached) can he used as toggle switches to lum several properties, such as hydrolytic stability and electrical conductivity, on and off. 

Although polyacetylene has served as an excellent prototype for understanding the chemistry and physics of electrical conductivity in organic polymers, its instability in both the neutral and doped forms precludes any useful application. In contrast to polyacetylene, both polyaniline and polypyrrole are significandy more stable as electrical conductors. When addressing polymer stability 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 applications require long-term chemical and electrochemical stability at room temperature while the polymer is immersed in electrolyte. Aerospace applications, on the other hand, can have quite severe stability restrictions with testing carried out at elevated temperatures and humidities. 

Two nitrogen-containing electroactive polymers, polypyrrole (PPY) [21] and polyaniline (PAN) [22], have been of particular interest because of their environmental stability, high electrical conductivity and interesting redox properties associated with the chain heteroatoms. More importantly, PAN has been found to exhibit solution processability [23, 24] and partial crystallinity [25,26]. 

The colorless, air-stable, volatile (61), usually abbreviated as MTO, has an outstanding thermal stability (dec > 300 °C) and is freely soluble in virtually any solvent from water to pentane. It is converted to Re04 in basic aqueous solution. In water at 70 °C, it forms an electrical conducting polymer of formula [Ho.5 Re(CH3)o.9203 ]oo. Photolysis homolyzes the Me-Re bond. However, the primary reaction brought about by irradiation into the UV absorption near 260 nm in a solid Ar matrix involves tautomerization of MTO to the methylidene hydroxo derivative H2C=Re(0)20H (62). ... 

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