Chemical synthesis, polymers electrochemical

P. Soudan, H. A. Ho, L. Breau and D. Belanger, Chemical synthesis and electrochemical properties of poly(cyano-substituted-diheteroarenethylene) as conducting polymers for electrochemical supercapacitors, J. Elec-trochem. Soc., 148, A775-A782 (2001). 

The synthesis of conducting polymers can be divided into two broad areas, these being electrochemical and chemical (i.e., non-electrochemical). Whilst the latter may be considered to be outside the scope of this review, it is worth noting that many materials which are now routinely synthesised electrochemically were originally produced via non-electrochemical routes, and that whilst some may be synthesised by a variety of methods many, most notably polyacetylene, are still only accessible via chemical synthesis. In view of this it is useful to have an appreciation of the synthesis of these materials via routes which do not involve electrochemistry. 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

Wnek 180> proposed that the structure of the oxidized insulating form of conventionally formed polyaniline is approximately a 50 % copolymer of diamine and diimine units, corresponding to the emeraldine structure and Hjertberg et al.180 obtained CPMAS NMR evidence for this conclusion. Some confirmation of the structure has also been obtained by chemical synthesis of the polymer182). However, Kitani et al.183) have suggested that the normal electrochemical synthesis leads to partially cross-linked polymers. 

Sherman, B. C., W. B. Euler, and R. R. Force. 1994. Polyaniline—A conducting polymer electrochemical synthesis and electrochromic properties. Journal of Chemical Education 71 (4) A94-A95. 

Electrochemical polymerisation produces films on an electrode surface.. Under controlled conditions uniform films up to a few mm thick, which carl be removed from the electrode for subsequent study, can be prepared. Physical properties can be modified by choice of the counterions (dopants) included in the film during growth. It is, however, more difficult to control chain structure and crosslinking than in chemical methods. Electrochemically produced polymers are, therefore, less well characterised than the best directly-synthesised polymers. While this is less satisfactory for fundamental investigations, it is of less concern for applications such as battery electrodes, artificial muscles and drug release agents. The two main approaches, direct-synthesis and electrochemical, are described in the following two sections. 

As one looks back over the last few decades it is possible to see trends emerging in the ionic liquids that are used and the main foci of interest. Early chloroaluminate systems with potential electrochemical applications gave way to ionic liquids with more air stable anions, with interest moving on to chemicals synthesis and catalysis. Then came new systems with specific properties to use as Task Specific Ionic Liquids (see Chapter 3), or for dissolving biomass polymers (Chapter 10), or as engineering fluids of various types. A small number of papers have now appeared on mixtures of ionic liquids. The exciting thing about ionic liquids is that as each development has occurred it has been in addition to the previous activities and not a replacement for these. 

Polypyrrole and many of its derivatives can be synthesized via simple chemical or electrochemical methods [120]. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but less developed. Different synthesis routes produce polypyrrole with different forms chemical oxidations generally produce powders, while electrochemical synthesis leads to films deposited on the working electrode and enzymatic polymerization gives aqueous dispersions [Liu. Y. C, 2002, Tadros. T. H, 2005 and Wallace. G. G, 2003]. As mentioned above the electrochemical polymerization method is utilized extensively for production of electro active/conductive films. The film properties can be easily controlled by simply varying the electrolysis conditions such as electrode potential, current density, solvent, and electrolyte. It also enables control of thickness of the polymers. Electrochemical synthesis of polymers is a complex process and various factors such as the nature and concentration of monomer/electrolyte, cell conditions, the solvent, electrode, applied potential and temperature, pH affects the yield and the quality of the film... 

Section 2 mainly focuses on generic synthesis of conducting polymers chemical oxidation and electrochemical polymerization. Although a large amount of work has been devoted to characterize physical and chemical properties of newly developed conducting polymers, this part only describes the information of synthetic methodology of conducting polymers. 

The ECPs are synthesized from their monomer units by a variety of techniques. Monomer units are joined together to form the polymer chain network, which constitutes the formation of ECPs. Various procedures are available for the synthesis, which include (i) chemical polymerization, (ii) electrochemical polymerization, and (iii) photopolymerization. 

The synthesis of conductive polymers is divided into two categories— chemical polymerization and electrochemical polymerization [8,9]. Many conductive polymers can be synthesized by both chemical and electrochemical methods. In chemical synthesis, monomers are polymerized using appropriate catalysts or reagents. The morphological, physical and electro-... 

The homopolymer films of sulfonated poly(3,4-ethylenedioxythio-phene) were electrochemically polymerized using a mixture of acetonitrile and water (5 1 ratio), as reported by Kumar et al. [31]. The UV-Vis spectra and the molecular weight of 15 800 g/mol confirmed the polymeric nature of the deposited films. The polymer was found to be soluble in water. The electrochemical and chemical synthesis of water-soluble, highly conductive oligomers of sulfonated poly(3,4-ethylenedioxythiophene) in aqueous acid and nonaqueous media has been reported by Zotti et al. [32]. In aqueous HCIO4 solution, the constant potential electrolysis of the sodium salt of sulfonated... 

The poly(4-carboxy-2,2 -bithiophene) can be prepared by direct chemical or electrochemical polymerization of 4-carboxy-2,2 -bithiophene (Figure 4.34) [51]. Hutchison et al. have suggested that this approach reduces undesirable side reactions and allows facile incorporation of strong electron-withdrawing side chains. Chemical synthesis was carried out using anhydrous ferric chloride in chloroform. The electrochemical polymerization was carried out in propylene-carbonate-containing tetra-butyl ammonium hexafluorophosphate. The conductivity of a pressed pellet of chemically synthesized polymer was approximately 10 " S/cm and the polymer was water soluble in its neutral form. 

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