Chemical polymerization polypyrrole

In all cases of electrochemicaHy or chemically polymerized unsubstituted polypyrrole, the final polymer is intractable in both the conducting and insulating forms. In contrast, a broad number of substituted polythiophenes have been found to be processible both from solution and in the melt. The most studied of these systems ate the poly(3-alkylthiophenes) (P3AT). 

The discovery that doped forms of polypyrroles conduct electrical current has spurred a great deal of synthetic activity related to polypyrroles [216-218], Reviews are available on various aspects of the synthesis and properties of polypyrroles [219,220]. In addition, summaries of important aspects of polypyrroles are included in several reviews on electrically conducting polymers [221-226]. Polypyrrole has been synthesized by chemical polymerization in solution [227-231], chemical vapor deposition (CVD) [232,233], and electrochemical polymerization [234-240]. The polymer structure consists primarily of units derived from the coupling of the pyrrole monomer at the 2,5-positions [Eq. (84)]. However, up to a third of the pyrrole rings in electrochemically prepared polypyrrole are not coupled in this manner [241]. 

Composites of polypyrrole and poly(vinyl chloride) have been prepared by several groups (64-67). Polythiophene-poly(vinyl chloride) composites have also been prepared (68). The electropolymerization of pyrrole on poly(vinyl chloride)-coated electrodes yielded composites with mechanical properties (tensile strength, percent elongation at break, percent elongation at yield) similar to poly(vinyl chloride) (65) but with a conductivity of 5-50 S/cm, which is only slightly inferior to polypyrrole (30-60 S/cm) prepared under similar conditions. In addition, the environmental stability was enhanced. Morphological studies (69) showed that the polypyrrole was not uniformly distributed in the film and had polypyrrole-rich layers next to the electrode. Similarly, poly(vinyl alcohol) (70) poly[(vinylidine chloride)-co-(trifluoroethylene)] (69) and brominated poly(vinyl carbazole) (71) have been used as the matrix polymers. The chemical polymerization of pyrrole in a poly(vinyl alcohol) matrix by ferric chloride and potassium ferricyanide also yielded conducting composites with conductivities of 10 S/cm (72-74). 

Polypyrroles (PPy s) are formed by the oxidation of pyrrole or substituted pyrrole monomers. In the vast majority of cases, these oxidations have been carried out by either (1) electropolymerization at a conductive substrate (electrode) through the application of an external potential or (2) chemical polymerization in solution by the use of a chemical oxidant. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but are less developed. These various approaches produce polypyrrole (PPy) materials with different forms—chemical oxidations generally produce powders, whereas electrochemical synthesis leads to films deposited on the working electrode, and enzymatic polymerization gives aqueous dispersions. The conducting polymer products also possess different chemical/electrical properties. These alternative routes to PPy s are therefore discussed separately in this chapter. 

Hanks has investigated the chemical polymerization of complexes 253-256.143144 With appropriate oxidizing agents (e.g., phosphomolybdic acid or /-butyl ammonium persulfate), film-forming conductive (10 2 to 10 3Scm 1) polypyrroles were generated. The polymer from Pd11 complex 255 was luminescent, while the other polymers were nonemissive. Dodecylbenzenesulfonate counterions improved the film quality of cast polymers. 

Pyrrole has been chemically polymerized with oxidants including sulfuric acid [87], bromine and iodine [88], copper(II) perchlorate [89], and iron(III) chloride [90]. Soluble polypyrrole can be prepared by the introduction of flexible side chains [91-93]. In contrast with the progress made in the synthesis of regioregular PTs, all 3-substituted polypyrroles reported so far have a regio-random structure. 

Anionic metal complexes, such as tetrasulfophthalocyanine or disulfoferrocene, can be incorporated from solution during the oxidative eleetro-chemical polymerization of pyrrole [24-27]. After re-reduction of the polypyrrole film the phthalocyanine derivative remains in the film, and the observed electrochemical conductivity is explained by ion transport of small electrolyte cations [26]. 

Polypyrrole/CNT nanocomposite Cond. Ss 0.9 3000 ppm 3000 ppm 50 s 90s Chemical polymerization, drop-casting [66]... 

Thus, optimization of all of the parameters in one experiment is difficult. In contrast, chemical polymerization does not require any special instruments it is a rather simple and fast process. Chemical polymerization method involves oxidative polymerization of pyrrole monomer by chemical oxidants either in aqueous or non-aqueous solvents or oxidation by chemical vapor deposition in order to produce bulk polypyrrole as fine powders. Fe(III) chloride and water are found to be the best oxidant and solvent for chemical polymerization of pyrrole respectively regarding desirable conductivity characteristics. 

Polypyrrole (PPy)/carbon nanotubes (PPy-CNT) In-situ chemical polymerization Spin casting NO [16]... 

Polypyrrole/iron oxide (PPy-FeO) In-situ chemical polymerization Pellet Humidity, CO, N, and CH, [20]... 

Polypyrrole-iron oxide In-situ chemical polymerization Pellet N3, O3, and CO3 [38]... 

TiOj/polypyrrole In-situ chemical polymerization LBL deposition CO and NH [74]... 

Park J. H., Ko J. M., Parka 0. 0., and Kim D. W., Capacitance properties of graphite/polypyrrole composite electrode prepared by chemical polymerization of pyrrole on graphite fiber, J. Power Sources, 2002, 105,20-25. 

Kudoh, Y. 1996. Properties of polypyrrole prepared by chemical polymerization using aqueous solution containing Fe2(S04)3 and anionic surfactant. Synth Met 79 17. 

Chu, X., V. Chan, L.D. Schmidt, and W.H. Smyrl. 1995. Crystalline fibers in chemically polymerized ultrathin polypyrrole films. J Appl Phys 12 6658. 

Films prepared in a similar manner with Hydrin C are those utilizing poly(N,N -dimethyl-2,2 -bipyrrole) [220], and polypyrrole [221]. Electrochromic films of Hydrin C and poly(o-methoxyaniline) have also been produced in which the aniline polymer is chemically polymerized in the presence of p-toluene sulfonic acid and blended with Hydrin C with the blend cast from solution [219]. Another example in which an electrochromic polymer was electrochemically polymerized in the presence of an insulating polymer is that of polypyrrole-polyjether urethane) or polypyrrole-poly(ethylene-co-vinyl alcohol) composite films [222]. Both films switched between a yellow reduced state to a bluish brown oxidized state, similar to polypyrrole. 

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