Electroactive polymers properties

The covalent chemistry of fullerenes has developed very rapidly in the past decade in an effort to modify fuUerene properties for a number of applications such as photovoltaic cells, infrared detectors, optical limiting devices, chemical gas sensors, three-dimensional electroactive polymers, and molecular wires [8, 25, 26, 80-82]. Systematic studies of the redox properties of Cgo derivatives have played a crucial role in the characterization of their unique electronic properties, which lie at the center of these potential applications. Furthermore, electrochemical techniques have been used to synthesize and separate new fullerene derivatives and their isomers as well as to prepare fullerene containing thin films and polymers. In this section, to facilitate discussion of their redox properties, Cgo derivatives have been classified in three groups on the basis of the type of attachment of the addend to the fullerene. In group one, the addends are attached via single bonds to the Cgo surface as shown in Fig. 6(a) and are referred to as singly bonded functionalized derivatives. The group includes... 

The main electroactive polymers, known for their actuating properties, are listed below ... 

Redox polymers are electroactive polymers for which the redox centers are localized on pendent, covalently attached redox centers. The electrochemical properties of such materials depend not only on both the loading and the nature of the redox-active center but also on the type of polymer backbone. The electroactive groups are typically metal complexes, which are covalently attached to a polymer... 

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]. 

In considering the potential applications of electroactive polymers, the question always arises as to their stability. The deterioration of a physical property such as conductivity can be easily measured, but the chemical processes underlying it are not as easy to be revealed. In order to understand them, XPS has been used to follow the structural changes which occur in the polymer chain and the counter-ions of the doped polymer. The following sections present some XPS findings on the degradation of electroactive polymers, such as polyacetylene, polypyrrole, polythiophene and polyaniline, in the undoped and doped states. 

In this review, some of the electroactive polymers most commonly studied during the past one and a half decades have been selected to illustrate the type and level of information obtainable from XPS core-level spectra. It concerns (a) the intrinsic structure, (b) the CT interaction, and (c) the stability and degradation behavior. The review is meant to be comprehensive, although emphasis has been placed on some specific issues related to these three basic physicochemical properties. For example, the chemical nature of the nitrogens in PPY and PAN has been critically compared on the basis of XPS data. Some of the major discrepancies in the XPS literature of electroactive polymers have also been examined. In most cases, preference has been given to results for which proper justification and careful comparison with available data are possible. Finally, some future trends in the application of XPS and other more surface sensitive techniques to the study of highly reactive conjugated polymer surfaces have been mentioned. 

More recently, there has been growing interest in a new type of redox polymer that is a hybrid of materials from PTs and will be referred to as conjugated metallopolymers. The key feature of this class of material is that the metal is coordinated directly to the conjugated backbone of the polymer, or forms a link in the backbone, such that there is an electronic interaction between the electroactive metal centers and the electroactive polymer backbone. This can enhance electron transport in the polymer, enhance its electrocatalytic activity, and lead to novel electronic and electrochemical properties <1999JMC1641>. 

High and low molecular weight electroactive polymers containing pendant 2-(7-benzothiazolyl-9,9 -dioctylfluorene) units have been prepared. These materials display electroluminescent properties that are useful in electronic devices. 

Intercalation of electroactive polymers such as polyaniline and polypyrrole in mica-type layered silicates leads to metal-insulator nanocomposites. The conductivity of these nanocomposites in the form of films is highly anisotropic, with the in-plane conductivity 10 to 10 times higher than the conductivity in the direction perpendicular to the film. Conductive polymer/oxide bronze nanocomposites have been prepared by intercalating polythiophene in V2O5 layered phase, which is analogous to clays. °° Studies of these composites are expected not only to provide a fundamental understanding of the conduction mechanism in the polymers, but also to lead to diverse electrical and optical properties. 

The trimethylsilyloxy (TMSO) group is stable under the coupling conditions in acetonitrile (Table 4, number 11). After oxidative dimerization the TMS ether can be mildly hydrolyzed (H and H2O) to the phenol or converted to a dibenzofuran. 1,2-Dialkoxybenzenes have been trimerized to triphenylenes (Table 4, numbers 9, 12, and 13). The reaction product is the triphenylene radical cation, which is reduced to the final product either by zinc powder or in a flow cell consisting of a porous anode and cathode [60]. Dibenzo-crown ethers are converted by anodic oxidation to electroactive polymers. Films of these polytriphenylenes exhibit unusual doping properties 62-64]. 

Under current investigation are the synthesis and properties of multimetallic thin films containing Ru, Os1, and Re1 in a wide variety of coordination environments. Judicious choice of such materials may lead to creation of an electroactive polymer film which would exhibit a bandlike spectrum of reversible, metal-centered redox processes extending from ca. -0.6 to +1.5 V. 

As intensive studies on the ECPs have been carried out for almost 30 years, a vast knowledge of the methods of preparation and the physico-chemical properties of these materials has accumulated [5-17]. The electrochemistry ofthe ECPs has been systematically and repeatedly reviewed, covering many different and important topics such as electrosynthesis, the elucidation of mechanisms and kinetics of the doping processes in ECPs, the establishment and utilization of structure-property relationships, as well as a great variety of their applications as novel electrochemical systems, and so forth [18-23]. In this chapter, a classification is proposed for electroactive polymers and ion-insertion inorganic hosts, emphasizing the unique feature of ECPs as mixed electronic-ionic conductors. The analysis of thermodynamic and kinetic properties of ECP electrodes presented here is based on a combined consideration of the potential-dependent differential capacitance of the electrode, chemical diffusion coefficients, and the partial conductivities of related electronic and ionic charge carriers. 

Conductivity within conducting electroactive polymers (CEPs) is a complex issue. A polymer that can exhibit conductivity across a range of some 15 orders of magnitude most likely utilizes different mechanisms under different conditions. In addition to the electronic conductivity exhibited by CEPs, they possess ionic conductivity because of the solvent or electrolyte incorporated during synthesis. The experimental parameters encountered during synthesis (as listed and discussed in Chapter 2) have an effect on the polymer conductivity. In particular, the electrochemical conditions, the solvent, the counterion, and monomers used during synthesis influence the electronic properties of the resulting polymer. 

As with polypyrrole (PPy), the electrical, chemical, and mechanical properties of polyaniline (PAn) are inextricably linked. In addition, PAn has spectacular optical and chromic properties that distinguish it from other conducting electroactive polymers (CEPs). The current state of knowledge concerning properties of PAn is reviewed in this chapter. 

Rapid advances in synthetic polymer science and nanotechnology have revealed new avenues of development in conductive electroactive polymers that take greater advantage of this versatile class of materials unique properties This third edition of Conductive Electroactive Polymers Intelligent Polymer Systems continues to provide an in-depth understanding of how to engineer dynamic properties in inherently conducting polymers from the molecular level. 

Unless materials are chemically stable in service environments, their otherwise useful properties (strength, ductility, magnetic and electronic behavior, etc.) may be lost. This section describes research opportunities and needs associated with metastable metallic alloys, metal-matrix composites, electroactive polymers, and high-performance ceramics. 

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