Conductivity polypyrrole derivatives

Potential technological applications of conducting polymers often require films that are strong and flexible. TTie mechanical properties of polypyrrole and other conducting polymers show a strong dependence on the nature of the counterion. For example, when toluenesulfonate is used as the counteranion, the mechanical properties are improved over previously synthesized materials. Such conducting polypyrrole derivatives have mechanical properties comparable to those of commercially available filled polymers that have been loaded with conducting carbon particles [85]. 

The critical role of the latter process was clearly shown in the extremely elegant work of Wegner and Riihe (1989) who measured the temperature dependence of the DC conductivity of a range of polythiophene and polypyrrole derivatives as a function of the interchain separation. The derivatives... 

Polypyrroles are a class of conjugated polymers that have been extensively studied due to their low oxidation potential leading to stable conductors, along with the compatibility of their electroactivity in aqueous media. Since the first report on the electrochemical preparation of conductive polypyrrole films [84—87], interest in the electronic properties of this polymer and its derivatives has increasingly grown. 

A number of other conducting polymer derivatives have been used for immobilizing enzymes and redox mediators for biosensor applications. Among these polymers are poly (tyramine) [167] and poly(l-(5-aminonaphthylethanoic acid) [168], which have accessible amine and carboxyl functionalities, respectively, for covalently linking to complementary groups on available amino acid residues of enzymes. Polypyrrole and polythiophene derivatives have also been widely exploited for covalent immobilization of enzymes, which then function as the sensing layers in efficient biosensors [169,170]. 

Juttner, K., and C. Ehrenbeck. 1998. Electrochemical measurements of the ion conductivity, permselectivity and transference numbers of polypyrrole and polypyrrole derivatives. / Solid State Electrochem 2 60. 

In the same report, the authors describe the homopolymerization of 3-(pyrrol-1-yl)propanesulfo-nate via oxidative coupling with ferric chloride (Figure 20.33). A black insoluble precipitate in a dark solution was obtained. The latter was claimed to be the first water-soluble polypyrrole derivative. Pressed pellets of the insoluble traction and cast films of the soluble portion possessed electrical conductivities of 10 to 10 S cm . ... 

Functional polymers appeared in the second half of the twentieth century. Although polyaniline was first described in the mid-nineteenth century by Henry Letheby and polypyrrole derivatives were reported to be electrically conducting in 1963 by B.A. Bolto et al. (1963), substantial progress was not made with intrinsically conducting polymers until the pioneering work of Hideki Shirakawa, Alan J. Heeger, and Alan MacDiarmid who reported similar high conductivity in oxidized iodine-doped polyacetylene in 1977 (Shirakawa 1977). For this research, they were awarded the 2000 Nobel Prize in Chemistry for the discovery and development of conductive polymers. ... 

The specific type of surface active pyrrole derivative used to form the monolayer was found to strongly influence the chemistry that is initiated at the air-water interface. For example, when solutions containing a 5000/1 mole ratio of pyrrole/3-octadecylpyrrole were spread onto the oxidizing subphase, copolymerization of the two monomers occurred as well as homopolymerization of the unsubstituted pyrrole monomer. The net result was a relatively thick surface film (100-200A) that was very difficult to transfer into multilayers via a conventional vertical lifting technique. With 3-octadecanoylpyrrole as the surface active component, on the other hand, copolymeiization of the two monomers was suppressed and only electrically conducting polypyrrole chains were formed. In this latter case, uniform monolayer films about 40 A thick were formed and these could be readily transferred into multilayer structures. The chemical structures of the molecules used in this particular system are presented in Scheme 3. 

ORIENTATION STUDIES OF LB FILMS FABRICATED WITH SURFACE ACTIVE PYRROLES AND POLYPYRROLE. The molecular organizations of multilayer thin films of the surface active pyrrole derivatives used to formed mixed monolayers with electrically conductive polypyrrole chains and ferrocene derivatized pyrroles have also been examined by FTIR reflection/absorption techniques. The materials investigated in... 

Monolayers of the surface active pyrrole derivatives 3-octadecyl pyrrole and 3-octadecanoyl pyrrole have also been successfully transferred into Y-type multilayer thin films. FTTR measurements have shown [23,24] that these materials both form highly ordered molecular organizations, each with its own specific type of molecular orientation. To illustrate these differences, the Fl lR reflection and transmission spectra of multilayer films of 3-octadecyl pyrrole (3-ODP) and 3-octadecanoyl pyrrole (3-ODOP) are displayed in Figure 12. Also included in this figi are the reflection and transmission spectra of a multilayer film of electrically conductive polypyrrole made with a 5000/1 mole ratio of pyrrole/3-octadecanoyl pyrrole using the proc ure described earlier. 

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. 

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

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. 

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

First report on a conducting polymer, viz oxidised iodine doped polypyrrole by D.E. Weiss et al., a polyactetylene derivative Development of Thermoplastic Vulcanizates, a new class of thermoplastic elastomers by Gessler, Fisher, Coran and Patel. 

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. 

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]. 

A major goal of the research on conducting polymers has been the development of a rechargeable plastic battery. Cells based on polypyrrole and lithium electrodes have been developed in which the energy per unit mass and discharge characteristics are comparable to nickel-cadmium cells. Current interest appears to center around stable, processable polymers, such as polythiophene and its derivatives, and polyaniline. 

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... 

Oxide, flouride, and polymeric films, as well as certain others, are used as protective coatings for HTSC materials (for example, see [505]). The electrodeposition of conducting polymers such as polypyrrole [433,491, 493, 506], polythiophene and its derivatives [493, 507], and polyaniline [478] is the most effective process. Anodic electropolymerization in acetonitrile solutions proceeds without any degradation of the HTSC substrate and ensures continuous and uniform coatings. Apparently, this method is promising not only for the fabrication of compositions with special properties based on HTSC [50, 28,295] as mentioned above, but also for the creation of junctions with special characteristics [507]. 

---