Electrochemically-Synthesized Polymers

Glatzhofer et al.1281 describe the reduction of conductivity of polypyrrole films, doped with poly(styrene-p-sulfonate), as increasing concentrations of dioxane are added to the aqueous electrolyte. They claim that the solvent induces a conformational change in the counterion, which modifies the film morphology. 

Tourillon 136,398) has reported that polythiophene films formed electrochemically are smooth up to 200 nm thick, after which they become rough and eventually powdery, at thicknesses above a few pm. The films have a density of about 1.5 g cm-3. Undoped films of polymethylthiophene show fibrils of 25 nm diameter which swell to 80 nm on doping to 25 mol % with perchlorate conter-ions. 

The electrical conductivity of polythiophene is much higher in the plane of the film (about 10 S cm 1) than perpendicular to the film (10 S cm ). X-ray diffraction shows a slight preferential chain orientation in the plane of the film and the structure appears to be layered under some preparation conditions 399). 

Satoh et al.400) have reported yield strengths of 80 MPa for undoped polythiophene, increasing to 1-70 MPa after drawing to 60 %. The redoped drawn film had a conduc- 

Poly(p-phenylene), synthesised electrochemically, is generally reported as a smooth film, although published micrographs indicate a fused globular morphology157 167 . 

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Refs. [i] Inzelt G, Pineri M, Schultze JW, Vorontyntsev MA (2000) Elec-trochim Acta 45 2403 [ii] KanerRB (1990) Preparation and properties of electrochemically synthesized polymers. In Linford RG (ed) Electrochemical science and technology ofpolymers-2. Elsevier, London, pp 97-147 [iii] Inzelt G (2008) Conducting polymers, Springer, Berlin Heidel-berg... 

S. Panero, P. Prosperi and B. Scrosati, Characteristics of electrochemically synthesized polymer electrodes in lithium cell. VI. Effects of synthesis conditions on the performance... 

S. Ivanov, P. Mokreva, V. Tsakova, and L. Terlemezyan, Electrochemical and surface structural characterization of chemically and electrochemically synthesized polymer layers -a comparison. Thin Solid Films, 441, 44-49 (2003). 

Recently, Turbiez et al. [27] reported a poly(3,4-ethylenedioxythiophene) (PEDOT) like polymer, poly(3,6-dimethoxythieno[3,2-h]thiophene), which exhibited a discernible vibronic fine structure with max at 592 nm (Figure 11.7) and a band-edge gap of 1.65 eV. The electrochemically synthesized polymer was reported as pale blue in the oxidized form, while the spectrum of the oxidized polymer remained unchanged even after 1 week, indicative of a potential transparent semiconductor like PEDOT. 

Panero, S., et al. 1992. Properties of electrochemically synthesized polymer electrodes. Part VII Kinetics of poly-3-methylthiophene in lithium cells. J Appl Electrochem 22 189. 

Polypyrrole (PPy) is probably the most often electrochemically synthesized polymer within the huge family of the conducting polymers, while for most other monomers e.g. thiophene, aniline, etc.) the chemical syntheses are dominant. In addition, both electrochemical and chemical syntheses are quite symmetric in their approach, since with one exception, the chemical syntheses of PPy all use an oxidative route, thus mimicking the electrochemical process. 

TABLE 1 Electrochemically Synthesized Polymers and Their Physical Properties... 

When one tries to determine the structure of the materials, the undoping should be done as thoroughly as possible in order not to involve any impurities which may smear the spectral features characteristic of each polymer species. The structural and specfroscopic features of the doped form are then referred to the undoped (pristine) form. For this, the electrochemically synthesized polymer films are reduced either electrochemically [30] (cathode reduction) or chemically. The former method is carried out by reversing the polarity of the electrochemical cell after electrochemical synthesis of the polymer, the latter method being imdertaken by exposing the as-synthesized films to a reductant such as ammonia [31]. Hotta et al. [32,33], however, have pointed out that for the purpose of rigorous undoping,... 

The electrochemical voltammetric data on fabrics are shown in Table 12.21. This suggests the possiblity of the involvement of nitrogen PAn in the surface coordination to the substrate material to explain the negligible electrochromic response. Otherwise data indicate that the basic grafted polymer polyaniline is almost identical to the electrochemically synthesized polymer. 

Panero, S., Prosper , R, and Scrosati, B., Properties of electrochemically synthesized polymer electrodes — IX. The effect of surfactants on polypytrole films, Electrochim. Acta, 37, 419, 1992. 

Conducting polymers can be prepared by chemical or electrochemical techniques. Electrochemical synthesis provides easier routes when compared with chemical synthesis and allows control over film formation, especially relevant if polymers are required as thin films deposited on the surface of metallic substrates. However, electrochemically synthesized polymers are usually more porous, a feature that requires consideration when a barrier effect is necessary. Another important aspect in the corrosion field is that the application of potential/current necessary to promote electropolymerization may accelerate dissolution (corrosion) of the metal. In some cases, an oxide pre-layer is deposited between the metal and the polymer to promote adhesion and hinder metal dissolution during the electropolymerization process (Tallman et al., 2002 Spinks et al., 2002). Alternatively, the application of layered coatings based on different conducting polymers can be a strategy to overcome the problem of metal dissolution. In the work of Lacroix et al. (2000), a layer of PPy was firstly deposited on zinc and mild steel in neutral conditions, followed by deposition of PANi in an acidic medium, because the direct deposition of PANi on those metallic substrates was not possible in an acidic medium, causing dissolution of the metal. 

Sharma PS, Pietrzyk-Le A, D Souza F, Kutner W (2012) Electrochemically synthesized polymers in molecular imprinting for chemical sensing. Anal Bioanal Chem 402... 

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