Preparation of Conductive Polymers

As well as viscosity, other factors to be aware of include the purity of the ionic liquids. The presence of residual halide ions in neutral ionic liquids can poison transition metal catalysts, while different levels of proton impurities in chloroalumi- 

The controlled synthesis of polymers, as opposed to their undesired formation, is an area that has not received much academic interest. Most interest to date has been commercial, and focused on a narrow area the use of chloroaluminate(III) ionic Hquids for cationic polymerization reactions. The lack of publications in the area, together with the lack of detailed and useful synthetic information in the patent Ht-erature, places hurdles in front of those with Hmited knowledge of ionic Hquid technology who wish to employ it for polymerization studies. The expanding interest in ionic liquids as solvents for synthesis, most notably for the synthesis of discrete organic molecules, should stimulate interest in their use for polymer science. 

Even within the small numbers of studies conducted to date, we are already seeing potentially dramatic effects. Free radical polymerization proceeds at a much faster rate and there is already evidence that both the rate of propagation and the rate of termination are effected. Whole polymerization types - such as ring-opening polymerization to esters and amides, and condensation polymerization of any type (polyamides, polyesters, for example) - have yet to be attempted in ionic liquids. 

This field is in its infancy and we look forward to the coming years with great anticipation. 

Commereuc, Y. Chauvin, G. Leger, J. Gaillard, Revue de L Institut Frangais du Petrole 1982, 37, 639-649. 

Commereuc, Y. Chauvin, E. Hugues, L. Saussine, A. Hirschauer, French Patent 1988, ER 2,611,700. 

As conducting media, often with large electrochemical windows, ionic liquids clearly have potential as solvents for electrosynthesis. One of the few areas in which this has been exploited is in the electrochemical synthesis of conducting polymers. 

The acidic ionic liquid [NBPY]Q-AlCl3 (X(A1C13) = 0.67) has been used as a solvent for the electrochemical polymerization of benzene to PPP as conductive films which were flexible and transparent. The films were prepared with very 

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An important area of research in silicon phthalocyanine chemistry has been the preparation of conducting polymers through Si—O—Si links.In one recent example, silicon phthalocyanine complexes have been appended to a den-drimer framework through Si—O—C(triazine) bonds formed by reaction of the salt Na [Si(Pc)(Ph)0 ] with a dichlorotriazine derivative. 

The Menschutkin reaction has been used to prepare poly(viologens) (115) directly (Scheme 31). These polymers were found to be quite useful as polyelectrolyte redox-polymers and for the preparation of conductive polymers when complexed with the 7,7, 8,8 -tetracyanoquinodimethane (TCNQ) radical anion (71MI11100). 

One of the most innovative and useful techniques for the preparation of conducting polymers has been the synthesis of highly soluble precursor polymers that can be easily handled in solution, purified, and then later converted to the less tractable conducting polymer. The first example of such an approach was the dehydrohalogenation of poly(vinyl chloride) (102). This reaction, like most elimination reactions on polymers, rarely goes to completion and is not well suited for the synthesis of useful conducting... 

Pyrrole is not polarographically reducible but can be reduced at a lead cathode in dilute sulfuric acid to pyrroline and further to pyrrolidine [203]. Under similar conditions 1,2-dimethylpyrroline [204] is also reduced to the pyrrolidine and indoles [205-207] to indo-lines or dimerized products [208]. 1-Methylindole can be reduced to 2,3-dihydro-1-methyl-indole in aqeuous THE at very negative potentials using TBAOH as electrolyte [209]. Pyrrole may also be oxidized anodically oxidation of pyrrole may result in the formation of polypyrrole useful for preparation of conducting polymers (Chapter 32). 

Considerable interest has arisen recently about the possibility of carrying out chiral syntheses on conducting polymer substrates. In these systems, the reacting solute is required to adsorb onto the surface in a well-defined orientation prior to electron transfer from the substrate. The design and preparation of conducting polymers that have the correctly oriented receptor groups promises to be an area of active research in the future, since such systems may represent convenient and economic routes to biologically active compounds. 

PHYSICAL PROPERTIES AND PREPARATION OF CONDUCTING POLYMER-BASED ELECTROCATALYTIC MATERIALS... 

The preparation of conducting polymers in emulsion is generally via an oxidative coupling mechanism in which the active polymerizing species are free-radicals. 

Porphyrins constitute a versatile building block for the preparation of conductive polymers. The large n system of... 

Polymeric films can be prepared at the surface of metal, glassy carbon, as well as carbon paste electrodes. The preparation of conducting polymers at the surface of carbon electrodes employed in biosensors is already reviewed [1]. The methods mostly used are solvent casting, spin coating, and electropol5mierization. 

Table 2. Methods for preparation of conducting polymer composites by chemical polymerization. 

Figure 17.2 Schematic illustration of common methods, such as hard-template, and soft-template methods as well as electrospinning technology, for the preparation of conducting polymer nanostructures.

Besides the electrochemical method, other methods such as the chemically initiated polymerization method, the vapor-phase methods, and the Langmuir-Blodgett method have been devised for the preparation of conducting polymers. In the chemical method, a chemical oxidant such as ferric chloride initiates the polymerization. Polymerization usually results in a powdery product and the resultant powder is then compressed into a pellet or dissolved in a suitable solvent such as methylene chloride or chloroform and spin coated on a substrate. In the vapor-phase technique, which is a variation of the chemical method, a monomer film is vacuum sublimed onto a glass substrate and then exposed to a solution or vapor of ferric chloride for oxidative polymerization. Films thus prepared are usually thick, of the order of micrometers. For some applications in which ultrathin and very uniform films are required, the Langmuir-Blodgelt technique for depositing monolayers has also been tried successfully [5]. 

Of the methods described for the preparation of conducting polymers, the most facile and often used is the electrochemical method. To understand the techniques one requires some familiarity with the terms used in electrochemistry. These terms are explained in Appendix I. Appendix II contains brief descriptions of the various electrochemical techniques used in the preparation and characterization of conducting polymers. A thorough discussion of the electrochemical fundamentals and techniques may be found in Bard and Faulkner [6]. 

In situ conductimetry is a convenient tool for studying the influence of different conditions on the preparation of conductive polymers. Conductivity is perhaps the best single parameter that describes the quality of a CP. In addition, the dopingundoping processes can be studied by monitoring conductance as potential is being scanned. Unfortunately, no commercial instrument directly applicable for in situ conductimetry is yet available, although it is possible to construct one from a commercial bipotentiostat and appropriate microelectrodes. The double-band platinum electrode can be constructed relatively easily without any special tools [7] (Fig. 12).. 

The preparation of conducting polymers as fibers and films is described in Ref. 129, where polyethylene of low density is used as a matrix. A Ti(OBu)4-AlEt3 catalytic system in mineral oil was prepared and polyethylene fibers were impregnated by the catalyst with subsequent polymerization of acetylene. The PE/PA fibers contain up to 82% PA. Doping of these fibers with for 40 min resulted in an increase of conductivity up to 12(X) S/cm, and the conductivity of PE/PA fibers stretched 2.2 times became 60(X) S/cm after doping. The fibers obtained in this way were shown to have good mechanical properties even with small amounts of the polymer carrier to keep high electrical conductivity. 

The products are useful intermediates for the preparation of conducting polymers. 

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