Electropolymerization of thiophene

One also obtains analogous findings with trace-crossing effects for the electropolymerization of thiophene and pyrrole. This cannot be explained by a simple linear reaction sequence, as presented in Scheme I, because it indicates competing homogeneous and heterogeneous electron transfer processes. Measurements carried out in a diluted solution of JV-phenylcarbazole provide a more accurate insight into the reaction mechanism (Fig. 2). 

Polymerization of thiophenes by oxidative coupling has been discussed earlier <1996CHEC-II(2)491>. The generally accepted mechanism for the electropolymerization of thiophene may also be valid in the case of chemical oxidative polymerization. The steps involved are formation of a radical cation, spin-pairing of two such radical cations to form a dihydrodimer dication, loss of protons with concomitant rearomatization, and repetition of this cycle with the dimer. Couplings take place at the position of highest unpaired-electron spin density. 

N. Sakmeche, E.A. Bazzaoui, M. Fall, S. Aeiyach, M. Jouini, J.C. Lacroix, J.J. Aaron, and P.C. Lacaze, Application of sodium dodecylsulfate (SDS) micellar solution as an organized medium for electropolymerization of thiophene derivatives in water, Synth. Met., 84, 191-192 (1997). 

The electropolymerization of thiophene-derivatives was conducted in a glove box using a two-electrode setup equipped with a Cu-mesh as counter electrode. The electrolyte used was the ionic liquid [BMIM][TFSI], which was deoxygenated by bubbling with nitrogen for 40 min and dried overnight with molecular sieves prior to use, containing 0.2M of either 2,2 -bithiophene or 3-methylthiophene [40]. Electrosynthesis was conducted under potentiostatic conditions at 3.2-3.4 V and 3.6-3.7 V for bi- and methylthiophene, respectively. Thereafter, the films were successively rinsed in [EMIM][BF4] and DI water, dried, and freed from their templated by dissolution in pure diethyl ether or a 2 1 mixture of diethyl ether and hexane. 

Fabrication of Superhydrophobic Surfaces by Electropolymerization of Thiophene and Pyrrole Derivatives... 

Historically, the electropolymerization of thiophene and bithiophene was first mentioned in 1982 [19] and 1983 [20], respectively. Following this initial work, many studies have been devoted to the analysis and optimization of the electropolymerization reaction. These studies have shown that the electropolymerization reaction is strongly dependent on experimental variables such as the solvent, concentration of reagents, temperature, nature and geometry of the working electrodes and applied electrical conditions [10]. 

The electropolymerization of thiophene monomers and the quality of the resulting polymer can be strongly influenced by the nature of the substituent grafted in the [ -position. The substitution of thiophene in the P-position may be of interest for several reasons (i) the electropolymerization can be more regioselective, (ii) introduction of electron-rich substituents decreases the oxidation potential of the monomer and (iii) the presence of substituents such as alkyl chains might improve the mechanical properties of the resulting polythiophenes. 

SCHEME 4 Electropolymerization of thiophene substituted with a chiral substituent. 

As mentioned above, conductive free-standing films can be obtained by electropolymerization of thiophenes substituted in the ] -position by a SiMe3 group. The polymers resulting from 2,5 coupling contain a large quantity of silicon. This property was recently used to... 

Role of Water. With increasing water content in acetonitrile the current efficiency for the galvanostatic electropolymerization of thiophene decreases rapidly, but much more slowly for the polymerization of 3-methylthiophene and bithiophene. The competition for radical cations generated from the monomer in the initial electrochemical step between the main reaction (the electropolymerization) and the side reaction (nucleophilic attack of the radical cation by water) explains this decrease in current efficiency [673]. A decrease in the monomer concentration increases the water/monomer ratio and impairs the electrical properties of PT. The presence of water in the electropolymerization process leads to more nonconducting and passivated films [264]. 

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. 

Anodic Electrochemical Oxidation. The anodic electropolymerization of thiophene presents several distinct advantages such as the absence of catalyst, direct grafting of the doped conducting polymer onto the electrode surface (which is of particular interest for electrochemical applications), easy control of the film thickness by deposition charge, and possibility to perform a first in situ characterization of the growing process or of the polymer by electrochemical and/or spectroscopic techniques. 

The electropolymerization of bithiophene was initially mentioned in 1980 [469], whereas the first report of the electropolymerization of thiophene appeared 2 years later [61]. Following these initial works, a large number of studies have been devoted to the analysis of the electropolymerization reaction and to the optimization of the electrosynthesis conditions [136]. 

A change from a polymerization process that occurs in the solution phase toward a process that occurs on the surface in the case of weakfy adsorbing electrodes like ITO-glass has been concluded from a variety of experimental details obtained by et al. [888] with spectroelectrochemical and surface analytical tools during electropolymerization of thiophene. 

Polymer-coated microelectrodes containing one or several monolayers fabricated by electropolymerization of thiophene, bithiophene and 3-methylthiophene at low potential with a low counterion content or with low afiinity ions, can be readily exchanged by ion-exchange technique by proteins, antibodies, antigens and drugs in order to immobilize these molecules [217]. 

Nicolas M (2008) Fabrication of superhydrophobic surfaces by electropolymerization of thiophene and pyrrole derivatives. J Adhes Sci Technol 22(3-4) 365-377... 

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