Polythiophene, chemical synthesis

R1r2nS02At and R N(S02Ar)2 Deposited polythiophenes Chemical synthesis at solid interfaces with convenient and selective regeneration of amines [36]... 

If polymer materials are given good solubility, these materials can be purified by dissolution and subsequent reprecipitation. Therefore, differences in the synfiietic methods become less important. Although the electrochemical synthetic methods developed by many researchers are applicable to the synthesis of the soluble polythiophenes, chemical synthesis may be more advantageous. This is partly because a higher yield of the polymer materials is expected from chemical synthesis. These approaches were first pursued by Elsenbaumer and co-workers [15]. 

The use of the heteroaryl Heck reactions extends beyond fine chemicals synthesis. Polythiophenes were prepared starting from 3-octyl-2-iodotiophene by heating in the presence of palladium acetate and tetrabutylammonium chloride (6.91.),122 The arylation of benzothiophene has also been achieved under the same conditions.123... 

Pilard, J. E Marchand, G. Simonet, J., Chemical synthesis at solid interfaces. On the use of conducting polythiophenes equipped of adequate linkers allowing a facile and highly selective cathodic s-n bond scission with a fully regenerating resin process, Tetrahedron 1998, 54, 9401-9414... 

Although most metal-containing polythiophenes have been synthesized by electropolymerization on an electrode surface, there are many reasons to chemically synthesize these polymers. Chemical synthesis may allow isolation of soluble polymers, enabling complete solution characterization (GPC, light scattering, NMR, etc.) and facilitating conductivity studies. Moreover, it can enable improved thin-film preparation and film deposition onto nonconducting substrates. Finally, monomers that are unsuitable for electropolymerization may be polymerized by chemical methods. 

Chemical synthesis of highly conducting polythiophene containing various doping agents was performed... 

Chemical synthesis involves either condensation polymerization, where the growth of polymer chains proceeds by condensation reaction, or addition polymerization where the growth is dependent on radical, anion, cation formation at the end of polymer chain. Figure 13.4 is a schematic representation of the oxidative chemical polymerization of polythiophene [24]. In general, oxidative chemical polymerization is carried out in the... 

The chemical synthesis of self-doped polythiophene was first reported by Ikenoue et al. [21]. They synthesized self-doped poly(3-(3 -thienyl)pro-panesulfonate) in aqueous media using ferric chloride as an oxidizing agent. The electrochemical polymerization of the monomer, 3-(3 -... 

F ure 8.13. Various processing routes of the soluble polythiophenes in combination with the doping. The materials are assumed to be prepared oxidatively either by electrochemical polymerization or via chemical synthesis. Reprinted with permission from Reference 51. Copyright 1989 Materials Research Society. 

Because of their potential or real applications in various fields of technology, oligothiophenes (Th ) and polythiophene (PTh) have become the center of great interest in many laboratories ranging from chemical synthesis to device manufacturing [175,176]. The vibrational spectra of Th and PTh and of their innumerable functionalized derivatives have been recorded either for routine chemical characterization or for more detailed structural studies. Reference 42 provides a rather complete review of a few years of vibrational spectroscopy of these materials. 

In the quest for a soluble and processable conducting polythiophene, alkylthiophenes were polymerized. Poly(3-methylthiophene) (PMT) was chemically synthesized and was found to be insoluble [9, 20-22]. The first chemical synthesis of environmentally stable and soluble poly(3-alkylthiophenes) (PATs) [23-25] was reported by Elsenbaumer in 1985 (Scheme 4). Very shortly after this report, other groups [26, 27, 28] also reported both the chemical and electrochemical preparation of PATs. Poly(3-alkylthiophene), with alkyl groups longer than butyl, ean readily be melt- or solution-processed into films which after oxidation ean exhibit reasonably high electrical conductivities of 1-5 S cm [23-28]. 

Finally, the oxidative coupling with CuCla has also been used for the chemical synthesis of various polythiophenes. Thus the reaction of the bifunctional Li—Tj—Li 26, obtained in 92% yield by deprotonation of H-Tj-H 2, with two equivalents of n-BuLi, with cuprous chloride in anisole lead to poly(bithiophene) P2, an insoluble brown precipitate [Eq. (10)]. After extraction, the polymer was obtained in yields ranging from 25 to 50%. Its doping with AsFs afforded a polymer with a conductivity of 5 Scm which is somewhat lower than that determined for films grown electrooxidatively [53]. 

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). 

SCHEME 2.60 Synthesis of polythiophene via chemical oxidation polymerization. 

Thiophene, pyrrole and their derivatives, in contrast to benzene, are easily oxidized electrochemically in common solvents and this has been a favourite route for their polymerization, because it allows in situ formation of thin films on electrode surfaces. Structure control in electrochemical polymerization is limited and the method is not well suited for preparing substantial amounts of polymer, so that there has been interest in chemical routes as an alternative. Most of the methods described above for synthesis of poly(p-phenylene) have been applied to synthesise polypyrrole and polythiophene, with varying success. 

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