Polythiophenes, properties chemical

Studies of the chemical properties of polythiophenes have been limited. As with polypyrroles, a hydrophobic backbone is formed, and the polymer has ion-exchange properties. Modification of chemical properties by incorporation of appropriate counterions is not so readily addressable because polymerization must be carried out from nonaqueous solution and occurs at more anodic potentials compared to pyrrole. 

Mechanical Properties of Polythiophenes Chemical properties Switching properties Optical properties of polythiophenes... 

Other conducting polymers that have paying attention in composite preparation due to their remarkable physical and chemical properties are polypyrrole (PPy), polyvinylcarbazole (PNVCz), polythiophene (PTh), and their derivatives. 

Polymers being die most versatile and dynamic of all materials have a crucial role to play in tliis new area of science and technology. Obviously, even witliin this class of materials certain groups will emerge as being most appropriate. We believe conducting electroactive polymers (CEPs) is one of these groups of materials. Polymers such as polypyrroles (I), polythiophenes (II) and polyanilines (III) have unique properties that enable tlieir dynamic chemical properties to be studied, manipulated and controlled. 

Even with PPys or polythiophenes the presence of other functional groups on the 3 or 4 position can be used to adjust the chemical properties and the electrochemical switching properties. For example the addition of alkyl groups results in polymers that are more hydrophobic (9) and also more soluble in common organic solvents. We have also shown that the addition of carboxy groups introduces self doping to the polymer and therefore cation exchange properties (10,11). 

Polythiophene can be synthesized by electrochemical polymerization or chemical oxidation of the monomer. A large number of substituted polythiophenes have been prepared, with the properties of the polymer depending on the nature of the substituent group. Oligomers of polythiophene such as (a-sexithienyl thiophene) can be prepared by oxidative linking of smaller thiophene units (33). These oligomers can be sublimed in vacuum to create polymer thin films for use in organic-based transistors. 

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

Related Polymer Systems and Synthetic Methods. Figure 12A shows a hypothetical synthesis of poly (p-phenylene methide) (PPM) from polybenzyl by redox-induced elimination. In principle, it should be possible to accomplish this experimentally under similar chemical and electrochemical redox conditions as those used here for the related polythiophenes. The electronic properties of PPM have recently been theoretically calculated by Boudreaux et al (16), including bandgap (1.17 eV) bandwidth (0.44 eV) ionization potential (4.2 eV) electron affinity (3.03 eV) oxidation potential (-0.20 vs SCE) reduction potential (-1.37 eV vs SCE). PPM has recently been synthesized and doped to a semiconductor (24). 

Polythiophenes (including oligothiophenes) are one of the most studied and important classes of linear conjugated polymers [444,445], Versatile synthetic approaches to PTs (chemical [446] and electrochemical [447]), easy functionalization and unique, widely tunable electronic properties have been the source of tremendous interest in this class of polymers. 

Coated materials are evaluated in S-SBR and in 50 50 blends of S-SBR and EPDM rubbers. In blends, the partitioning of fillers and curatives over the phases depends on differences in surface polarity. In S-SBR, polythiophene-modified silica has a strong positive effect on the mechanical properties because of a synergistic reaction of the sulfur-moieties in the polythiophene coating with the sulfur cure system. In S-SBR/EPDM blends, a coating of polyacetylene is most effective because of the chemical similarity of polyacetylene with EPDM. The effect of... 

The structure/property relationships that govern third-order NLO polarization are not well understood. Like second-order effects, third-order effects seem to scale with the linear polarizability. As a result, most research to date has been on highly polarizable molecules and materials such as polyacetylene, polythiophene and various semiconductors. To optimize third- order NLO response, a quartic, anharmonic term must be introduced into the electronic potential of the material. However, an understanding of the relationship between chemical structure and quartic anharmonicity must also be developed. Tutorials by P. Prasad and D. Eaton discuss some of the issues relating to third-order NLO materials. 

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. 

The rationale for preparing this hybrid copolymer was to combine the desirable properties of polyaniline with those of polythiophene. For example, polythiophene has demonstrated thermo- and electrochromism, solvatochromism, luminescence, and photoconductivity while polyaniline has demonstrated reversible protonic dupability, excellent redox re-cyclability, and chemical stability. 

Summaries on the synthesis, properties, and uses of polythiophenes are included in two general reviews on poly thiophenes [259,260]. A synopsis of important aspects of polythiophenes are also included in several reviews on various aspects of conducting polymers [221-226], Cation radicals are the propagating species in both electrochemical and chemical oxidative polymerizations of thiophene and its derivatives. The polymer obtained by this method is linked primarily by a,a-linkages. However, other types of linkages (a,f3 and /3,/3) are present in varying amounts (Fig. 59). Substituted thiophene derivatives can couple in a head-to-tail or head-to-head manner. 

From the late 1970s onwards, efforts to synthesise conjugated polymers rapidly expanded and numerous new materials were prepared. Many of these still proved to be intractable substances that were difficult if not impossible to purify and characterise. The maximum levels of conductivity achieved on doping often fell well short of the metallic range. Such properties meant that the majority of these materials attracted little attention beyond the initial reports, and certainly no commercial interest. An example of the few polymers produced at this time that have been extensively studied subsequently is polythiophene (PTh), Fig. 9.2(h). Although this polymer was also reported in the nineteenth century (Meyer, 1883), the first reliable synthesis appeared in 1980, see McCullough (1998). Another example is polyfluorene, Fig. 9.2(i), which was prepared chemically and electrochemically in 1985, see Rault-Berthelot and Simonet (1986). Much subsequent synthesis has been directed to the inclusion of pendent groups to either enhance solubility,... 

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]. 

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