Electropolymerization of thiophene derivatives

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... 

The properties of surfactant molecules properties are (i) their ability to form different aggregate structures (micelles) above die critical micellar concentration (CMC), (ii) their ability to solubilize water-insoluble organic molecules (M) by hydrophobic-hydrophobic interactions, and (iii) their adsorption on electrodes changes the solution-metal interface, which alters redox reactions and produces template effects on the electrode surface (79) (Schem 2). SDS can be used to electropolymerize various thiophene derivatives such as EDOT, BT and MOT in aqueous solution. 

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... 

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. 

With the development of 3-(w-bromoalkyl)thiophenes [100], several new types of crown ether functionalized PTs have been synthesized. While electropolymerization of monomeric derivatives (32) failed, probably for steric reasons, bithiophene (33) and terthiophene (34) were easily electropolymerized to the corresponding crown ether derivatized PTs [101],... 

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

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... 

Polythiophenes with ferrocenes in the main chain 41 have been prepared by electropolymerization of bis-substituted ferrocene monomers, but only for the n = 2 and n = 3 monomers [78,79]. The resulting film of the n = 2 monomer showed a thiophene > Fe(III) LMCT band at 1395 nm. A soluble derivative of the n = 3 polymer has been prepared. The oxidized form is blue with a thiophene > Fe(III) LMCT band at 590 nm [80], In general, it has been found that these systems show greater delocalization, the longer the thiophene chain and the better is the matching of the ferrocene and thiophene redox potentials [81,82],... 

For the electrosynthesis of PEDOT and PPy, water was the preferred electrolyte solvent. Although some reports suggest that under special experimental conditions the aqueous electropolymerization of poly(thiophene) derivatives is possible, all attempts conducted in this study failed, including deposition at low pH values and using bithiophene which exhibits a lower oxidation potential than thiophene as the monomeric species [43, 44], Typically, boron trifluoride diethyl etherate and (fairly) anhydrous acetonitrile were used instead [34]. Although both solvents were successfully used to prepare poly(thiophene) inverse opals via the templated synthesis using poly(styrene) microsphere arrays, they tended to destroy the styrenic DG-structured scaffold [2 ]. 

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. 

The conditions for polymerization were also foimd to be crucial in relation to polythiophene and polybithiophene films [58,80,84,114-121], The relatively high potential required for the oxidation prevents the use of many metallic substrates. The electrochemical oxidation of substituted thiophenes and thiophene oligomers yields conducting polymers, and these compounds can be electropolymerized at less positive potentials, so it is a good strategy to use these derivatives instead of thiophene (see Sect. 2.2.6). Another approach is the deposition of a thin polypyrrole layer that ensures the deposition of polythiophene on these substrates (eg., Ti, Au) [115]. Interestingly, other polymers as well as copolymers and composites (see Chap. 2) can also be synthesized. 

The first study of PTh and PPy wettability was reported in 1984 [27]. Derivatives of thiophene and pyrrole were polymerized in a classical electrolytic medium, i.e. acetonitrile and tetrabutylammonium tetrafluoroborate as the electrolytic salt. The thickness of the film was approximatively 0.5 pm and the water contact angles reported (86° for PTh and 62° for PPy) indicate their hydrophilicity. These electropolymerized films have the advantage to show exceptional stability for several months. In the oxidized form, the films are ionic composites. Electrochemically... 

Terthiophene (2.179, n = 2) and EDOT (2.181) derivatives, in which 18-crown-6 moieties were attached directly to the 3,4-position of the central thiophene ring, were prepared by Zotti s group (Chart 1.37) [275]. These oligomers showed maximum absorption at 365 and 366 nm, respectively, which were significantly blue shifted (AA, = 20-30 nm) after the addition of 0.1 MNa" " or K+ ions. The polymer films prepared by electropolymerization of the oligomers were little influenced by the addition of alkali metal ions. Furthermore, electrochemical quartz crystal microbalance analysis of the alkali metal coordination ability of the polymer films in acetonitrile solution revealed a lower degree of coordination, which was attributed to the loss of degrees of freedom in the crown-ether moiety. 

Electropolymerization of Host-Guest Complexes (Thiophene derivatives -Cyclodextrins) in Aqueous Solutions... 

This approach is based on the use of the unique physical properties of surfactant molecules in aqueous solutions, which n es it possible to electropolymerize thiophene derivatives and to study the influence of micelles on the electropolymerization process and on the structures and properties of die resulting polymer films. 

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