Polymers from Thiophen Derivatives

Polymers from Thiophen Derivatives.—The bifunctionality of thiophen and its potential availability in large quantities at a low price has for many years attracted the interest of polymer chemists. However, progress has been slow. 2,5-Dichlorothiophen has been polymerized to a solid in 93% yield on treatment with aluminium chloride and cupric chloride in carbon disulphide. The product is believed to be poly-5-chloro-2,3-thienylene. Thiophen-2,5-dicarboxylic hydrazide was prepared by the reaction of thiophen-2,5-dicarbonyl chloride with the corresponding dihydrazide and then cyclodehydrated to poly-(thienylene-[2,5]-alt-l,3,4-oxadiazolylene-[2,5]-amer) (258) by polyphosphoric acid. This polymer could also be obtained directly from thiophen-2,5-dicarboxylic acid and hydrazine in oleum. The polymers produced were investigated in view of their thermal stability and as polymeric organic semiconductors. The same research 

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Polymers electropolymerized from thiophene derivatives, e.g. thiophene, 3-methyl-thiophene, 3,4-dimethylthiophene, and 2,2 -bithiophene, showed electrochromism with various colours and stabilities depending on the derivatives (Table 5) The oxidized state of poly(3-methylthiophene) was blue-green, and the reduced state was red. This polymer retains more than 80 % of its activity after 1.2x10 cycles of electrochromism between —0.2 and 0.8 V vs SCE. High stability as regards doping-undoping cycles was also reported for PT... 

The electrosynthesis of polythiophene (PT) from thiophene must be performed under extremely anhydrous conditions, quite in contrast to polypyrrole [334]. Polymerization of 3-methylthiophene and bithiophene is much less sensitive to water. The advantage of PT is a higher theoretical capacity and a very positive potential (cf. Table 7). It is for these reasons that its application as a positive electrode in rechargeable lithium batteries [335-338] and in a metal-free PPy/PT cell [339] has been considered. Derivatives such as dithienothiophene [340] or rra/is-l,2-di(2-thienyl)ethylene [341] have also been polymerized, but the polymer materials suffer from low theoretical capacities [337]. 

Polymers containing heterocycles in the backbone include a variety of compounds, as the diversity of heterocyclic molecules is quite large. The polymers from this class may contain groups derived from furan, thiophene, pyrrole, isoindole, benzimidazole, benzothiazole, benzoxazole, quinoxaline, etc. Macromolecules with a ladder backbone containing, for example, a phenoxazine unit in their structure also are known. Amino thermosetting resins from melamine can be considered as polymers containing heterocycles in their structure. 

Belletete, M., L. Mazerolle, N. Desrosiers, M. Leclerc, and G. Durocher. 1995. Spectroscopy and photophysics of some oKgomers and polymers derived from thiophenes. Macromolecules 28 8587-8597. 

One can also mention the case of composites-based conducting polymers electrodeposited and characterized on anodes of platinum- or carbon black- filled polypropylene from a stirred electrolyte with dispersed copper phthalocyanine. The electrolytic solution contained, besides the solvent (water or acetonitrile), the monomer (pyrrole or thiophene) and a supporting electrolyte. Patterned thin films were obtained from phthalocyanine derivatives, as reported in the case of (2,3,9,10,16,17,23,24-oktakis((2-benzyloxy)ethoxy)phthalocyaninato) copper . Such films were prepared by means of capillary flow of chloroform solutions into micrometer-dimension hydrophobic/hydrophilic channels initially created by a combination of microcontact printing of octadecylmercaptan (Cig-SH) layers on gold electrodes. These latter gave birth to a hydrophobic channel bottom while oxidative electropolymerization of w-aminophenol (at pH 4) led to hydrophilic channel walls. 

Many thiophene derivatives have been polymerized in order to obtain new materials tailored for different purposes. Roncali [596] reviewed the enormous amount of literature regarding the synthesis, functionalization and applications of polythiophenes in 1992. Beside the polymerizations of thiophene and bithiophene, polymers from several thiophene oligomers, substituted thiophenes, thiophenes with... 

A number of conjugated heterocyclic polymers, viz., poly(pyrrole) [9], poly(p-phenylene) [10], poly(thiophene) [11], and poly(aniline) [12] are also electrically conducting and continue to be developed and studied for electrochromic devices [13-14 see also the companion chapter in this volume] and ion switching devices [15-16], among others. Polymer films with high electrical conductivity have been generated by electrochemical polymerization of benzenoid, nonbenzenoid and heterocyclic aromatics, in particular from the derivatives of pyrrole, thiophene, carbazole, azulene, pyrene, triphenylene and aniline. The electrochemical approach for making these films is very versatile and it provides a facile way to vary the properties of the films. The realization of the applications for each electroactive polymer depends on the control and particularly the enhancement of the... 

Thiophene was found in tar, gas and industrial benzene obtained from coal in the nineteenth century. A large number of thiophene derivatives are described in the literature and their physical properties, nucleophilic substitution and biological activity are still of current interest [ ] As for polymers, thiophene was oxidized by such acidic materials as orthophosphoric acid or a synthetic silica-alumina catalyst to yield liquid oligomer which consisted of its trimer containing a small amount of its pentamer. A report on this was published as early as 1883 [2], However, modem studies on polythiophene, aiming at the preparation of electrically conductive polymers, started at the beginning of the 1980s [3-5]. 

Esterification and the consequent reduction of 3-thienylacetic acid produces 3-(2-hydroxyethyl)thiophene, which must be protected before electropolymerization. The resulting thin polymer film, e.g., of poly[3-(2-methoxyethyl)-thiophene], with protected OH groups, can be reacted to produce reactive hydroxy groups on its surface, such as poly[3-(2-hydroxyethyl)thiophene] [111] (cf. Table 3). Further thiophene derivatives with a protected OH group have been synthesized starting from 3-(2-hydroxyethylthiophene) 3-(2-benzyloxyethyl)-thiophene, 3-[2-triphenylmethyloxy)ethyl]thiophene, 3-[2-(trimethylsilyloxy)-... 

Polymers Derived from Precursor Polymers, 01igo(thiophene)s, or Poly(thiophene) Derivatives... 

Polythiophene has been synthesized chemically by polycondensation reactions of difunctionalized thio-phene derivatives (starting from 2.S-dihalothiophene) as well as by electropolymerization of thiophene itself. One may also start with bithiophene, terthiophene or higher oligomers of thiophene in order to prepare polymers with thiophene systems, but with differing properties, especially with regard to the electrochemical behaviour. 

Polythiophene and its derivatives show remarkable air stability in both oxidized and reduced form [111]. However, there are variable reports on their stability in different types of enviromnents. The ionization potential of poly thiophene is estimated to be above 5 eV, which is high enough to protect the polymer from forming a charge-transfer complex with otygen to cause oxidative instability. Both electrochemically as-prepared polythiophene and polythiophene redoped after ammonia compensation showed much better air stability compared to polyacetylene [112,113]. 

Some conducting polymers, as thiophene and thiophene derivatives, can be reduced from the neutral state of the chains (Arias-Pardilla et al. 2010) electrons are injected to the chains generating negative charges (n-doping) that must be compensated by entrance of cations from the solution forcing the osmotic entrance of solvent for osmotic balance. The reaction can be summarized as... 

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