Derivatives of polypyrrole

With the objective to inve.stigate the dependence of carrier transport on the interchain separation. Riihe et al [252,253] have synthesized doped (C104 ,PF5 ) poly(3,4-cycloalkylpyrrole)s having 3, 4, 5 or 10 methylene groups in the alkyl loop. These polymers arc also amorphous. Because of the interring torsions, the alkyl substituents are expected to form a cylindrical shell around the chain. The thickness of the shell has been estimated from single-crystal x-ray data of the monomers. The conductivity decreases w ith an increase of the shell thickness. This indicates the importance of interchain hopping for this property. 

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One approach to recognize vapors is to coat interdigitated electrodes with an electronically conductive polymer, such as a derivative of polypyrrole. 

Several groups have studied the synthesis of carboxylic acid derivatives of polypyrrole however, the electrochemistry of very few carboxylic acid substituted polypyrroles has been reported. Smith et al. [64] reported... 

In recent years there has been a lot of interest in substances with redox and ion-exchange properties that could serve as the mediation layer between the metallic electron conductor and an ion-exchange layer. These are conductive polymers based mostly on derivatives of polypyrrole, polythiophene and polyaniline (Figure. 8.4). The... 

Conductivities of polymers of technological interest such as polypyrrole and polythiophene are typically 1000 cm in the doped state, and the conductivity can be tuned by reversibly doping and undoping the polymer. Derivatives of these and other polymers have achieved even higher conductivities. 

There are large numbers of naturally occurring representatives, especially of pyrrole that include the important polypyrroles (porphyrins and corrins), and the nitropyrrole antibiotics such as pyr-rolomycins and pyrroxamycin. Derivatives of furan have been used as fungicides and A-vinylpyr-rolidone is an important monomer for the production of blood plasma extenders and for cosmetic applications. On account of the similarity in the pathways for the aerobic degradation of monocyclic furan, thiophene, and pyrrole, all of them are considered here. Anaerobic degradation of furans is discussed in Part 2 of this chapter. 

Several groups have recently shown (36,42,43,44) that photoanode materials can be protected from pRotoano3ic corrosion by an anodically formed film of "polypyrrole".(45) The work has been extended (46) to photoanode surfaces first"Treated with reagent that covalently anchors initiation sites for the formation of polypyrrole. The result is a more adherent polypyrrole film that better protects n-type Si from photocorrosion. Unlike the material derived from polymerization of I, the anodically formed polypyrrole 1s an electronic conductor.(45) This may prove ultimately important in that the rate of ionTransport of redox polymers may prove to be too slow... 

Polyacetylene has good inert atmospheric thermal stability but oxidizes easily in the presence of air. The doped samples are even more susceptible to air. Polyacetylene films have a lustrous, silvery appearance and some flexibility. Other polymers have been found to be conductive. These include poly(p-phenylene) prepared by the Freidel-Crafts polymerization of benzene, polythiophene and derivatives, PPV, polypyrrole, and polyaniline. The first polymers commercialized as conductive polymers were polypyrrole and polythiophene because of their greater stability to air and the ability to directly produce these polymers in a doped form. While their conductivities (often on the order of 10" S/m) are lower than that of polyacetylene, this is sufficient for many applications. 

In order to get high-quality polymer films, it is essential to select best conditions of the electrolytic solution, electrode potential, temperature, etc. For synthesizing the films of polypyrrole, polythiophene, polyazulene, and their derivatives,... 

The second method is the synthesis of copolymers or derivatives of a parent conjugated polymer with more desirable properties. This method is the more traditional one for making improvements to a polymer. It modifies the structure of the polymer to increase its processibility without compromising its conductivity or its optical properties. All attempts to do this on polyacetylene have failed as they always significantly reduced its conductivity. However, such attempts on polythiophenes and polypyrroles proved more fruitful. 

Streptomyces distallicus the structure elucidation and synthesis have also been made by them.165 A wide variety of porphyrins which are derivatives of porphin (125 R = H) occur in nature and exert three biological functions (a) oxygen storage and transport, as in hemoglobin, (b) cellular respiration as in the cytochromes, and (c) photosynthesis, as in the chlorophylls for detailed discussion of structures and synthesis of naturally occurring porphyrins, see references.166 Recent developments in the chemistry of polypyrrolic compounds have been reviewed.167 Several naturally occurring indole alkaloids have dimeric structures of type B,168 an example of which is c-toxiferine-I, a calabash curare alkaloid found in South American species of Strychnos.169... 

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]. 

Although some mechanistic details are still controversial, it has been established that the oxidative polymerization (chemically or electrochemically) of pyrrole and pyrrole derivatives proceeds via an E(CE) mechanism which involves cation-radical propagating species. The most commonly accepted mechanism of polypyrrole formation is illustrated in Fig. 57 [237,242]. The polymerization begins with the one-electron oxidation of pyrrole to produce cation radical 399. This cation radical has been... 

An established technique for preparing soluble derivatives of intractable polymers is to add solubilizing substituents to the monomer. Thus, insoluble polyphenylenes have been rendered soluble (75) in common solvents such as chloroform by phenyl substitution. Similarly, a wide range of substituted pyrroles and thiophenes have been investigated to improve the tractability of these relatively stable conducting polymers. The chemical and electropolymerization of N-substituted pyrroles (76) gave polymers with substantially decreased conductivities, generally by a fector of 10 compared to polypyrrole. However, monomers substituted at the 3 and 4 positions of... 

Recent development in multilayer sensor architecture using sequential electrochemical polymerization of pyrrole and pyrrole derivatives to entrap enzymes was tested on a tyrosinase-based phenol sensor [127]. A phenothia-zine dye, thionine served as redox mediator and was covalently attached to the thin, functionalized first polypyrrole layer on Platinum disk electrodes. Then, a second layer of polypyrrole with entrapped tyrosinase was electrochemically deposited. The phenol sensor constructed in this manner effectively transferred electron from enz3Tne to the electrode surface. As all steps in preparation, including deposition of the enzyme-containing layer are carried out electrochemically, this technique may prove to be applicable for mass production of miniature sensors. 

Polyaniline is less tolerant of preparation conditions than polypyrrole, and the list of anion dopants used in the preparation is more limited. However, subsequent replacement of the anion used in preparation by a dodecylben-zene sulfonate makes polyaniline become soluble in solvents such as Af-methyl pyrrolidone (NMP), or zn-cresol, and it can be spin-coated or otherwise solution-processed. In a similar way derivatives of aniline, such as... 

Abeysekera AM, Grigg R, Trocha-Grimshaw J, Viswanatha V (1976) Structure and reactivity of Rh(I) complexes of polypyrrole macrocycles and their /V-alkylatcd derivatives. Tet Lett... 

This chapter will focus on some recent developments in the synthesis of polyacetylene itself, (CH) , and of substituted derivatives, (CR) f(CH) [24, 25]. While the great variety of other conductive polymers, including poly(phenylene vinylenes), polythiophenes and polypyrroles, may be thought of as annulated derivatives of polyacetylene [26-28], (Fig. 10-4), their syntheses and properties differ enough to put them outside the scope of this chapter. The reader is referred to a number of reviews covering both these polymers and polyacetylene [15,17, 29]. 

Warren et al. [240] have explored some twenty ditferent sulphonates, mostly aromatic, in the preparation of films of polypyrrole as well as poly(3-methylthiophene), from aqueous solution and from acetonitrile solution. Only PPy-/ TS films from an aqueous medium show the splitting of diffraction peaks this is not interpreted further. Rather, the degree of order is estimated from the intensity of the diffraction peak. Benzenesulphonate ranks first in this respect. Dodecylbenzenesulphonate is also effective, and additionally shows a small-angle peak. This suggests that especially alkyl chains are effective in arranging themselves in a domain of hydrophobic character. (Dodecylbenzenesulphonic acid has been found to be an excellent surfactant for polyaniline and to facilitate its processing see Section 6.4.1.) Some of the films give spot patterns in electron diffraction. Warren et al. [240] state, however, that cell data cannot be derived from these. 

Since the initial discovery of polyacetylene doping by FeClj [92], ferric chloride still remains one of the most popular dopants for conjugated polymers. In addition, it is a very efficient oxidizing/polymerizing agent for the preparation of polypyrrole, polythiophene and their derivatives [32,84]. The most extensive Mbssbauer effect studies have therefore been carried out for FeCl, doped polymers. 

S. Takeoka, T. Kara, K. Yamamoto, and E. Tsuchida, Thermal stabilization of polypyrrole by incorporation of aromatic sulfonate derivatives as dopants, Chem. Lett., 25, 253 (1996). 

At the present time polyaniline is without doubt the most important conducting polymer from the point of view of large scale technological use however, derivatives of polythiophene and poly(phenylenevinylene) and indeed, polypyrrole, polyacetylene and poly-paraphenylene show considerable technological promise as specialty polymers, as described later. In view of the technological importance of polyaniline, its synthesis and properties will be emphasized in this review. 

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