Polypyrrole conjugated polymers

At this point it might be appropriate to comment on the conflicting requirements of the synthesis. The large interest which other conjugated polymers such as polypyrrole, polyanilinc or poly(parattracted originates, firstly, from their attractive physical properties, but also from the sim-... 

Polymers with n-conjugated backbones are an important class of materials that have captured the imagination of the scientific community due to their remarkable properties and exciting applications [91-95]. While most of the work on n-conjugated polymers has focused on all-carbon systems, there has been considerable interest in incorporating heteroatoms into the n-conjugated backbone (i.e.,polythiophene, polypyrrole, polyaniline) to tune their properties. 

In the area of ion sensing, cation recognition by electrodes containing functionalized redox-active polymers has been an area of considerable interest. Fabre and co-workers have reported the development of a boronate-functionalized polypyrrole as a fluoride anion-responsive electroactive polymer film. The electropolymerizable polypyrrole precursor (11) (Fig. 11) was synthesized by the hydroboration reaction of l-(phenylsulfonyl)-3-vinylpyrrole with diisopinocampheylborane followed by treatment with pinacol and the deprotection of the pyrrole ring.33 The same methodology was utilized for the production of several electropolymerizable aromatic compounds (of pyrrole (12) (Fig. 11), thiophene (13 and 14) (Fig. 11), and aniline) bearing boronic acid and boronate substituents as precursors of fluoride- and/or chloride-responsive conjugated polymer.34... 

Similar approach has also been taken by Ferain and Legras [133,137,138] and De Pra et al. [139] to produce nanostructured materials based on the template of the membrane with etched pores. Polycarbonate film was also of use as the base membrane of the template, and micro- and nanopores were formed by precise control of the etching procedure. Their most resent report showed the successful formation of ultrasmall pores and electrodeposited materials of which sizes were as much as 20 nm [139]. Another attractive point of these studies is the deposited materials in the etched pores. Electrochemical polymerization of conjugated polymer materials was demonstrated in these studies, and the nanowires based on polypyrrole or polyaniline were formed with a fairly cylindrical shape reflecting the side wall structure of the etched pores. Figure 10 indicates the shape of the polypyrrole microwires with their dimension changes by the limitation of the thickness of the template. 

Polyacetylene is very susceptible to attack by oxygen. The polymer loses its metallic lustre and becomes brittle when exposed to air. However, other conjugated polymers were found. Polypyrrole, polythiophene, polyaniline, polyphenylenevinylene (Figure 6.4), and others are conjugated polymers whose bonding and con-... 

Solitons are considered to be important defect states in these conjugated polymers (see Fig. 6.48). It has however been shown that correlation energy is the more important factor in giving rise to the energy gap in (CH) (Soos Ramasesha, 1983). Other polymers related to polyacetylene are polythiophene, polypyrrole, poly-phenylenesulphide, and polyparaphenylene (Section 3.3). Extensive measurements on doped polyacetylenes have been reported in the last five years and these materials, unlike other conducting polymers such as (SN), seem to have good technological potential. 

An extensive review of the synthesis of rc-conjugated polymers is presented using a tutorial approach to provide an introduction to the field intended for the undergraduate student and the experienced chemist alike. The many synthetic methodologies that have been used for the synthesis of conjugated polymers are outlined for each class of polymers with a focus on research from the 1990s. The effect of structure on electrical properties is detailed. Specific systems reviewed include the polyacetylenes, polyanilines, polypyrroles, polythiophenes, poly(arylene vinylenes), and polyphenylenes. 

Keywords Conducting polymers, Conjugated polymers, Polyacetylenes, Polyanilines, Polypyrroles, Polythiophenes, Poly(arylene vinylenes), Polyphenylenes... 

Although the original research on conductive polymers was done with polyacetylene, a number of other conjugated polymers have been developed for such uses. Among these products are the polythiophenes, polyanilines, polyphenylenevinylenes, polyethylene-dioxythiophenes, polypyrroles, and polydialkylfluorenes. These products are now beginning to find applications in a number of industrial, research, medical, and consumer devices. 

Several conjugated polymers such as polyaniline, polypyrrole and poly thiophene have been prepared by chemical methods using doping. The electrical conductivity of these polymers has been controlled by (i) the type of dopant, (ii) the concentration of doping, (iii) the conditions of doping (the current density, temperature of reaction, etc.)... 

Conjugated polymers with a degenerate ground slate have a slightly different mechanism. As with polypyrrole, polarons and... 

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. 

The first conducting polymer was trans-polyacetylene which was doped with bromine and was produced at 1970s. Soon other conjugated polymers such as poly (p-phenylene), polypyrrole (PPy), polyethylene dioxythiophene (PEDOT) and polyaniline (PANi) and their derivatives which are stable and processable were synthesized. The molecular structures of a few ICPs are shown in Figurel. 

Similar structures will occur in conjugated polymers such as polypyrroles and polythiophenes prepared from monomers with one or more different substituents at the positions on the aromatic ring not involved in the polymerisation, see Fig. 1.5. The reactivity of one particular site in the monomer usually predominates, so that the effect is relatively small. A 1 % head-to-head content may, however, seriously upset crystallisation. 

Using a different approach, the research gronps of Fabre and Freund have synthesized boronate-functionalized conjugated polymers, which serve as electrochemical sensors. For example, a conjugated redox-active film of polypyrrole (174) was electrodeposited onto a platinum electrode from acetonitrile solution. Addition of fluoride anions led to a new redox system that showed an anodic shift relative to polypyrrole itself, which was attributed to fluoride binding to the boronate group. A related poly(aniline boronic acid) (175) was also reported and studied for saccharide detection. " ... 

It has been mentioned already that polypyrrole (25) and polythiophene (26) play an important role as electrical conductors and polymeric anodes in battery cells [2,47,226]. Since the charging and discharging of the conjugated polymer is accompanied by the incorporation and removal of counterions it is clear that the material can also act as a carrier of chemically different anions which influence the physical, chemical and physiological properties of the material [292]. With regard to the full structural elucidation of the polymers it must be added, however, that the electropolymerization process of pyrrole and thiophene does not provide a clean coupling of the heterocycles in the 2,5-positions. Instead, the 3- and 4-position can also be involved giving rise to further fusion processes under formation of complex polycyclic structures [47]. 

The formation of conductive conjugated polymers [e.g., polyacetylene, polypyrrole, polythiophene, polyaniline and poly(p-phenylene)] [92, 94] on electrodes by electropolymerization has been studied thoroughly [95]. If the electropolymerization is performed in a solution containing both the monomer and enzyme, then enzymes present in the immediate vicinity of the electrode surface become trapped in the... 

Some conjugated polymers, such as polythiophene and polyaniline were synthesized already in the last century [8a,b], It is not surprising that, for example, polyaniline has played a major role in research directed toward synthetic metals because it possesses a relatively stable conducting state and it can be easily prepared by oxidation of aniline, even in laboratories without pronounced synthetic expertise (see section 2.6). It is often overlooked, however, that a representation of, for example, polypyrrole or polyaniline by the idealized structures 1 and 2 does not adequately describe reality, since various structural defects can occur (chart 1). Further, there is not just one polypyrrole, instead each sample made by electrochemical oxidation must be considered as a unique sample, the character of which depends intimately on the conditions of the experiment, such as the nature of the counterion or the current density applied (see section 2.5). Therefore, one would not at all argue against a practical synthesis, if the emphasis is on the active physical function and the commercial value of a material, even if this synthesis is quick and dirty . Care must be exercised, however, to reliably define the molecular structure before one proceeds to develop structure-property relationships and to define characteristic electronic features, such as effective conjugation length or polaron width. 

As mentioned in the introduction, the electrical conductivity upon doping is one of the most important physical properties of conjugated polymers. The conductivity ranges from lOOOOOS/cm for iodine-doped polyacetylene [41], 1000 S/cm for doped and stretched polypyrrole [42], to 500 S/cm for doped PPP [43], 150 S/cm for hydrochloric acid doped and stretched polyaniline [44], and 100 S/cm for sulfuric acid doped PPV [45] to 50 S/cm for iodine-doped poly thiophene [46]. The above listed conductivities refer to the unsubstituted polymers other substitution patterns can lead to different film morphologies and thus to a different electrical conductivity for the same class of conjugated polymer in the doped state. 

Properties of representative conducting polymers. Doped conjugated polymers have generated substantial interest in view of possible applications such as lightweight batteries, antistatic equipment, and microelectronics to speculative concepts such as molecular electronic devices.37-38 These polymers include doped polyacetylene, polyaniline, polypyrrole, and other polyheterocycles (Figure 5). While the conduction mechanism of metals and inorganic semiconductors is well understood and utilized in microelectronics, this is not true to the same... 

This significant low-field conductivity demonstrates that conjugated polymers can be encapsulated in nanometer channels and still support mobile charge carriers. In contrast to the experiments with polypyrrole in zeolite Y and mordenite (see above), the channels in the MCM host provide more space and apparently allow some important interchain contact to occur. 

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