Properties of Polypyrroles

The assembly of polypyrroles (PPy s) is an intricate process and determines the molecular structure and microstructure of the polymer obtained. This in turn influences the chemical, electrical, and mechanical properties of the material. It is impossible to optimize a single property of materials such as polypyrrole (PPy) in isolation. The chemical, electrical, and mechanical properties are inextricably linked. 

To function as intelligent materials, conducting polymers must be capable of stimuli recognition, information processing, and response actuation. As a result, they must possess appropriate chemical properties that change in response to stimuli and appropriate electrical properties that allow information to be transported within the structure and switches to be actuated. The mechanical properties must also be considered, because the creation of materials with ideal chemical and electrical properties, but with inappropriate mechanical properties, will be of questionable value. 

To fully optimize the material properties, the relationships between the structure and the properties must be thoroughly understood. The current state of knowledge concerning the electrical, chemical, and mechanical properties of PPy structures are reviewed in this chapter. 

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Significant variations in the properties of polypyrrole [30604-81-0] ate controlled by the electrolyte used in the polymerization. Monoanionic, multianionic, and polyelectrolyte dopants have been studied extensively (61—67). Properties can also be controlled by polymerization of substituted pyrrole monomers, with substitution being at either the 3 position (5) (68—71) or on the nitrogen (6) (72—75). An interesting approach has been to substitute the monomer with a group terminated by an ion, which can then act as the dopant in the oxidized form of the polymer forming a so-called self-doped system such as the one shown in (7) (76—80). 

Following the discovery of the unique electronic properties of polypyrrole, numerous polymers of pyrrole have been crafted. A copolymer of pyrrole and pyrrole-3-carboxylic acid is used in a glucose biosensor, and a copolymer of pyrrole and A-methylpyrrole operates as a redox switching device. Self-doping, low-band gap, and photorefractive pyrrole polymers have been synthesized, and some examples are illustrated [1,5]. 

Table 1. Structures and electrochemical properties of polypyrroles and polythiophenes...

Fig. 11.8. Current density as a function of rotation rate during growth of electrodeposited polypyrrole film at 0.550 ( ), 0.600 ( ), 0.650 (T), and 0.700 ( ) V. (Reprinted with permission from D. J. Fermin, M. Mostany, and B. Scharifker, Electronically Conducting Polymers Synthesis and Electrochemical Properties of Polypyrrole, Curr. Topics Electrochem. 2 132-136, 1993.)...

Several studies have focused on the mode of formation and properties of polypyrrole polymers. Studies of the effects of temperature on polypyrrole conductivity have shown that the polymer formed by electropolymerization of pyrrole and camphor sulfonate as dopant at low temperature has higher conductivity and is stronger than that formed at higher temperatures. X-ray scattering shows that interlayer distance increases with increasing temperature <2002IAS155>. 

The discovery that doped forms of polypyrroles conduct electrical current has spurred a great deal of synthetic activity related to polypyrroles [216-218], Reviews are available on various aspects of the synthesis and properties of polypyrroles [219,220]. In addition, summaries of important aspects of polypyrroles are included in several reviews on electrically conducting polymers [221-226]. Polypyrrole has been synthesized by chemical polymerization in solution [227-231], chemical vapor deposition (CVD) [232,233], and electrochemical polymerization [234-240]. The polymer structure consists primarily of units derived from the coupling of the pyrrole monomer at the 2,5-positions [Eq. (84)]. However, up to a third of the pyrrole rings in electrochemically prepared polypyrrole are not coupled in this manner [241]. 

H. Yoneyama, K. Wakamoto, and H. Tamura, Photoelectrochemical properties of polypyrrole-coated silicon electrodes, J. Electrochem. Soc. 132 2414, 1985. 

To get more detailed information about the N NMR chemical shift behavior and physical properties of polypyrrole in the solid state, quantum... 

The following chapters will describe how the design and assembly of various important polymers can be used to produce predetermined properties. (The synthesis and properties of polypyrroles, polyanilines, and polythiophenes are discussed in detail and differences between these systems emphasized.) A multitude of other CEP systems exist, and the interested reader is referred to the extensive literature now available. Furthermore, the synthesis of CEPs to produce different forms that enable integration of all the functions required for intelligent operation or that allow incorporation into a larger structure will be described. 

The growth and the surface properties of polypyrrole on single crystal graphite electrodes as studied by in-situ electrochemical scanning probe microscopy... 

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