Chemical oxidative polymerization

In the chemical oxidative pol5unerization a monomeric precursor of the conducting polymer is polymerized by an oxidizer. Ions of the oxidizer or additional ions act as dopants. The monomer and oxidizer can be brought into the porous anode structure either sequentially or as a premixed reactive solution. 

Chemical polymerization reaction of EDOT to PEDOT (left) using Fe(III) toluenesulfonate (right) as oxidizer. 

In the sequential process the anode pellet is, for example, first dipped into an oxidizer solution, then the solvent is evaporated and the pellet is dipped into EDOT. If further impregnation cycles are necessary, residual precursor material and reduced oxidizer salts can be washed out after polymerization to open the pore structure of the anode pellet for new material. 

Nevertheless the sequential process is widely applied in industry. The main reason is that premixed reactive solutions of EDOT and oxidizer are not sufficiently stable. Moreover typically a better electrical performance of the capacitor is achieved by the excess of EDOT, which favors the formation of nonconjugated EDOT oligomers as intermediates (see Chapter 8). 

Eor the premixed solution process, monomer and oxidizer are mixed in a solvent prior to the application to the anode pellet. - In such mixtures EDOT and oxidizer can be used in a stoichiometric ratio to ensure 100% EDOT usage. Then the anode pellet is dipped into the solution and dried. If further impregnation cycles are necessary, residual salt of the oxidizer is washed out after the polymerization. 

The possible mechanisms of the oxidative pol mierization using ferric chloride has been proposed, as shown in Fig. 3.20. 

The mechanisms are based on two assumptions. First, since pol5mierization was observed only in solvents where the catalyst was either partially or completely insoluble (chloroform, toluene, carbon tetrachloride, pentane, and hexane, not diethyl ether, xylene. 

Since the most negative carbon of the neutral 3-methylthiophene is also carbon 2, and the carbon with the highest odd electron population of the RC is carbon 2, it was concluded that an RC mechanism would lead to mostly 2-2, HH links. The calculated total energies of the species with the radicals at the 2 and 5 carbons indicated that the latter was more stable by 1.5 kj/mol. Therefore, the more stable radical could react with the neutral species, forming head-to-tail couplings, as shown in Fig. 3.21.  

Due to the difficulties of studying a system with a heterogeneous, strongly oxidizing catalyst that produces difficult-to-characterize rigid-rod polymers, the mechanism of oxidative polymerization is not easy to decide. However, the RC mechanism seems to be the likely route for PTh synthesis. 

3-mTh was electrodeposited in the form of both a homopolymer and a copolymer to examine electrochemical, spectroelectrochemical, and electrochromic properties in common electrochemical solvents. 

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The synthesis involves the nickel-catalyzed coupling of the mono-Grignard reagent derived from 3-alkyl-2,5-diiodothiophene (82,83). Also in that year, transition-metal hahdes, ie, FeCl, MoCl, and RuCl, were used for the chemical oxidative polymerization of 3-substituted thiophenes (84). Substantial decreases in conductivity were noted when branched side chains were present in the polymer stmcture (85). 

SCHEME 2.60 Synthesis of polythiophene via chemical oxidation polymerization. 

In general, polypyrrole can be prepared via electrochemical or chemical oxidative polymerization of pyrrole involving different highly reactive intermediates. Also, the pyrrole/cyclodextrin complex can be polymerized in aqueous solution under oxidative conditions by adding potassium peroxodisulfate as an ox-... 

Polymerization of thiophenes by oxidative coupling has been discussed earlier <1996CHEC-II(2)491>. The generally accepted mechanism for the electropolymerization of thiophene may also be valid in the case of chemical oxidative polymerization. The steps involved are formation of a radical cation, spin-pairing of two such radical cations to form a dihydrodimer dication, loss of protons with concomitant rearomatization, and repetition of this cycle with the dimer. Couplings take place at the position of highest unpaired-electron spin density. 

Summaries on the synthesis, properties, and uses of polythiophenes are included in two general reviews on poly thiophenes [259,260]. A synopsis of important aspects of polythiophenes are also included in several reviews on various aspects of conducting polymers [221-226], Cation radicals are the propagating species in both electrochemical and chemical oxidative polymerizations of thiophene and its derivatives. The polymer obtained by this method is linked primarily by a,a-linkages. However, other types of linkages (a,f3 and /3,/3) are present in varying amounts (Fig. 59). Substituted thiophene derivatives can couple in a head-to-tail or head-to-head manner. 

Instead of chemical oxidative polymerization, electropolymerization can also be considered. A recent study shows that slow but efficient electropolymerization is possible if anilinium-exchanged zeolite Y is subjected to oxidative treatment at the electrode-electrolyte interface. Cyclic voltammetric signatures of the polymerization suggest that it occurs mostly through one dimer (p-aminodiphenylamine) which imdergoes oxidative polymerization. Electrochemical polymerization of aniline in zeolite molecular sieves was studied. A zeolite-modified electrode showed shape-selectivity for 12-molybdophosphoric acid. 

Higuchi A, Iwata N, and Nakagava T. Electroconducting polyaniline composite films prepared by chemical oxidative polymerization at gas/liquid interface. J. Appl. Polym. Sci. 1990 41 1073-1086. 

Not surprizingly, in view of the preceding preference for hydrophobic surfaces, PAn can also be deposited by the in situ method on supports such as low-density polyethylene (LDPE).35 Modification of the LDPE surface by grafting with acrylic acid promotes the growth and adhesion of the PAn films. Conducting PAn coating may be similarly deposited on PVC and PMMA surfaces through chemical oxidative polymerization.36... 

A. Yasuda and T. Shimidzu, Chemical oxidative polymerization of aniline with ferric chloride, Polym. J., 1993, 25, 329. 

Polyaniline In situ chemical oxidative polymerization method Phenol >400 [591]... 

Poly(3- hexylthiophene) Chemical oxidative polymerization with anhydrous FeCl3 as oxidant, 3-hexylthiophene as monomer and chloroform as solvent Methyl orange >400 [595]... 

Chemical Oxidative Polymerization of Aniline Hard (Physical) Template Methods... 

Nanoporous Hard-Template Methods PANI-NTs have been prepared by the chemical oxidative polymerization of aniline within the pores of PC nanoporous membranes... 

PANI nanoribbons, also known as nanobelts, have been synthesized by a self-assembly process using the chemical oxidative polymerization of aniline in a surfactant gel, formed by mixing an acetic acid solution of anihne and CTAB with an aqueous solution of APS... 

The synthesis of spiral PANl nanostructures (2-D ordered spirals comprised of singlestrand PANI-NFs) by chemical oxidative polymerization using a hydrated surfactant sodium dodecylsulfonate crystallite template was recently described [406]. It was found that a spiral dislocation structure on the surface of a hydrated sodium dodecylsulfonate crystallite was responsible for the growth of the spiral PANl nanoarchitecture. It was revealed that APS has a strong tendency to induce the formation of a spiral dislocation stmcture in hydrated sodium dodecylsulfonate crystallites. A mechanism of adsorption of oligoanilines on the steps of dislocation has been proposed for the growth of PANl spirals. 

Composites of PANI-NFs, synthesized using a rapid mixing method, with amines have recently been presented as novel materials for phosgene detection [472]. Chemiresistor sensors with nanofibrous PANI films as a sensitive layer, prepared by chemical oxidative polymerization of aniline on Si substrates, which were surface-modified by amino-silane self-assembled monolayers, showed sensitivity to very low concentration (0.5 ppm) of ammonia gas [297]. Ultrafast sensor responses to ammonia gas of the dispersed PANI-CSA nanorods [303] and patterned PANI nanobowl monolayers containing Au nanoparticles [473] have recently been demonstrated. The gas response of the PANI-NTs to a series of chemical vapors such as ammonia, hydrazine, and triethylamine was studied [319,323]. The results indicated that the PANI-NTs show superior performance as chemical sensors. Electrospun isolated PANI-CSA nanofiber sensors of various aliphatic alcohol vapors have been proven to be comparable to or faster than those prepared from PANI-NF mats [474]. An electrochemical method for the detection of ultratrace amount of 2,4,6-trinitrotoluene with synthetic copolypeptide-doped PANI-NFs has recently been reported [475]. PANI-NFs, prepared through the in situ oxidative polymerization method, were used for the detection of aromatic organic compounds [476]. 

G. Ciric-Marjanovic, A. Janosevic, B. Maijanovic, M. Trehova, J. Stejskal, and P. Holler, Chemical oxidative polymerization of dianilinium 5-sutfosahcylate, Russ. J. Phys. Cherre A, 81, 1418-1424 (2007). 

G. Ciric-Maijanovic, M. Trchova, and J. Stejskal, The chemical oxidative polymerization of aniline in water Raman spectroscopy, J. Raman Spectrosc., 39, 1375-1387 (2008). 

L.B. Kong, J. Zhang, JJ. An, Y.C. Luo, and L. Kang, MWNTs/PANI composite materials prepared by in-situ chemical oxidative polymerization for supercapacitor electrode, J. Mater. ScL, 43, 3664-3669 (2008). 

K.R. Reddy, K.P. Lee, Y. Lee, and A.I. Gopalan, Facile synthesis of conducting polymer-metal hybrid nanocomposite by in situ chemical oxidative polymerization with negatively charged metal nanoparticles. Mat. Letters, 62, 1815-1818 (2008). 

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