Electropolymerization 3-methylthiophene

Fig. 3 Regioregular poly [3-(2-methyl-1 -butoxy)-4-methylthiophene] (PMBMT) synthesized via oxidative electropolymerization...

Leventis. N., Dass, A., and Chandrasekaran. N. 2007. Mass transfer effects on the electropolymerization current efficiency of 3-methylthiophene in the magnetic field. Journal of Solid State Electrochemistry 11, 727-735. 

As with polypyrroles, the counterion used during electropolymerization influences the conductivity of polythiophenes.120121 Electrochemically produced copolymers122 of 3-dodecylthiophene (DTh) and 3-methylthiophene (MTh) have been shown to exhibit conductivities intermediate to the two homopolymers. The actual value depends on the ratio of MTh to DTh in the polymer. 

In a third procedure, an adhesion promoter of a 3-(ethyl-phosphonic-acid)thiop-hene was applied to the metal surface followed by an electrochemical film preparation [65]. The following procedure was used in this case Mild steel was mechanically polished, then the specimen were treated for 60 minutes in a solution of 3-(ethyl-phosphonic-acid)thiophene. Afterwards, a layer of poly(3-methylthiophene) was formed by electropolymerization in an electrolyte consisting of 0.1 mol 1 3-methylthiophene, 0.1 moll tetrabutyla-mmonium-hexafluorophosphate (N(Bu)4 PFg) in dichloromethane (CH2CI2). 

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. 

Lu, B., Chen, S., Xu, J., Zhao, G., 2013. Thermoelectric performances of different types of polyselenophene and its copolymers with 3-methylthiophene via electropolymerization. Synth. Met. 183,8-15. 

Fig. 1 Ultrathin conducting polymer heterolayers by the potential sweep programmed electropolymerization of pyrrole (25mM) and 3-methylthiophene (50mM) in CH3CN containing lOOmM LiC104. Potential sweep programs and TEM pictures of their cross sections.

A flow chart demonstrating the protocol is shown in Fig. 6. The procedure has been demonstrated for poly(3-methylthiophene) films, by analysis of frequency response as a function of time during film electropolymerization short (long) time responses represent the acoustically thin (thick) film scenario [24]. Film mass (whether or not directly accessible from A/ data) defines the product hypy, so (as shown in Fig. 6 [24]) a plot of hy versus py is a hyperbola. As film mass (polymer coverage) increases, a series of hyperbolae are generated. The acoustically thin film data (A/ and Q) define the unique solution (of the infinity of solutions on the hyperbola) for p as indicated in Fig. 6 [24] this value is projected across all the hyperbolae. 

Finally, electrocatalysis has been used in electropolymerization processes. As an example of this, the cation radical of terthiophene has been used to mediate the electropolymerization of 3-methylthiophene [59], and a gold complex has also been used to mediate PPy formation [60]. Like analogous works in this direction [50] this did not seem to lead to major improvements in the film s characteristics nor properties (this latter aspect will be further detailed in Section 18.3.3). 

The electrocatalytic behavior of ECPs toward the electropolymerization of other monomers has also been mentioned and recently investigated by Zotti et al. [59] it has been demonstrated that electropolymerization of 3-methylthiophene could be catalyzed by previously electrodeposited polyterthio-phene because of the formation of a charge transfer complex during the electropolymerization process (see also Section 18.2). 

Usually substituted thiophenes (e.g., 3-methylthiophene) or bithiophene are used in electropolymerization since the oxidation process leading to the formation of cation radicals and polymerization occms at less positive potentials [521,522,525, 528,531,533,535,538,541,546,563,583,586,596]. 

The cyclic voltammograms and the changes that occur to them during repetitive cycling are similar to those of 3-methylthiophene oxidation in acetonitrile. When a platinum electrode is used, the color change (red-blue) due to the redox transformation of poly (3-methylthiophene) is easily visible. A visual inspection also reveals that the electropolymerization reaction starts at the three-phase junction, as theoret-... 

Uehara, K., Ichikawa, T., Serikawa, T Yoshikawa, S., Ehara, S., andTsunooka, M. (1998) Redox reaction at the two-layer interface between aluminum and electropolymerized poly(3-methylthiophene) thin solid films. Thin Solid Films, 322,198-205. 

Shi et al. have developed another method for the electrochemical polymerization of high oxidation potential monomers in boron fluoride ethyl ether (BFEE) which could yield highly conducting PT films (Scheme 9.4) [32]. As observed in the case of the electropolymerization of 3-methylthiophene, bithiophene 2T and terthiophene 3T, such improvement stems from the lower oxidation potentials at which the electropolymerization occurs in BFEE compared with those required in common electrolytes. Recent development of this strategy by the Reynolds group has shown that thiophene, 3-methylthiophene, 3-bromothiophene and 3,4-dibromothiophene can be polymerized in BFEE to yield homogeneous, electroactive polymer films, where their electrochemical polymerization in common electrochemical solvents has proved much more difficult [33],... 

A number of approaches have been proven effective, in some cases, a judicious choice of electrolyte or current density is sufficient For example, within a limited current density window, it is possible to electropolymmze aniline in neutral aqueous solution. (3). Poly-3-methylthiophene can be deposited from highly acidic aqueous solution if a stable suspension is achieved before electropolymerization (4), or as d cribed in chapto 3 of this volume, from sodium dodecyl sulfrte micelles in a less harsh medium. Micelles have also proven useful where addition of non-ionic sur ctants to the monomer solution have been employed in the preparation of poly(3,4-ethylene dioxythiophene) (PEDOT) from aqueous perchlorate solutions (5). 

The morphology of the polymer has, at times, a profound effect on its conductivity or electron-transfer characteristics. When a uniform layer with a small grain size is desired, pretreatment of the electrode surface with acid before electropolymerization has been proven to be effective in the deposition of polypyrrole( toluene sulfonate) on mild steel (S), while the aqueous method for production of poly-3-methylthiophene from acidic aqueous solution mentioned above also has the benefit of producing very uniform (3-4 pm) particles (4J. Uniformity in grain size is also a function of die deposition method. For both 3-methyl thiophene and for ppolypyrrole, use of a brief potential step in the presence of sinall anionic species for production of the polymer has r ulted in a production of a dense, uniform film (9, lOJ, A very thin uniform layer of polymer with an poly (N-phenylpyrrole) sur ce has been obtained by electropolymerization of 4-... 

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