Polypyrroles and poly

The polymers which have stimulated the greatest interest are the polyacetylenes, poly-p-phenylene, poly(p-phenylene sulphide), polypyrrole and poly-1,6-heptadiyne. The mechanisms by which they function are not fully understood, and the materials available to date are still inferior, in terms of conductivity, to most metal conductors. If, however, the differences in density are taken into account, the polymers become comparable with some of the moderately conductive metals. Unfortunately, most of these polymers also have other disadvantages such as improcessability, poor mechanical strength, instability of the doped materials, sensitivity to oxygen, poor storage stability leading to a loss in conductivity, and poor stability in the presence of electrolytes. Whilst many industrial companies have been active in their development (including Allied, BSASF, IBM and Rohm and Haas,) they have to date remained as developmental products. For a further discussion see Chapter 31. 

Komori and Nonaka132,133 electrochemically oxidized methyl, isopropyl, n-butyl, isobutyl, r-butyl and cyclohexyl phenyl sulfides (108) and cyclohexyl p-tolyl sulfide (109) to their sulfoxides using a variety of polyamino acid-coated electrodes to obtain the range of e.e. values shown in parentheses. The highest enantiomeric purities were obtained using an electrode doubly coated with polypyrrole and poly(L-valine), an electrode which also proved the most durable of those prepared. 

Very low asymmetric induction (e.e. 0.3-2.5%) was noted when unsymmetrical sulphides were electrochemically oxidized on an anode modified by treatment with (— )camphoric anhydride or (S)-phenylalanine methyl ester299. Much better results were obtained with the poly(L-valine) coated platinum electrodes300. For example, t-butyl phenyl sulphide was converted to the corresponding sulphoxide with e.e. as high as 93%, when electrode coated with polypyrrole and poly(L-valine) was used. 

Several alkyl aryl sulfides were electrochemically oxidized into the corresponding chiral sulfoxides using poly(amino acid)-coated electrodes448. Although the levels of enan-tioselection were quite variable, the best result involved t-butyl phenyl sulfoxide which was formed in 93% e.e. on a platinum electrode doubly coated with polypyrrole and poly(L-valine). Cyclodextrin-mediated m-chloroperbenzoic acid oxidation of sulfides proceeds with modest enantioselectivity44b. 

Polymers consisting of but not limited to poly thiophene, polypyrrole and poly aniline have been extensively used to make polymer nanofibers. In general, any metal that can be electroplated has most likely appeared in a nanowire. Semiconductors, polymers, and insulators have also been used in the design of nanowires.Furthermore, different metals can be plated in succession to give striped nanowires. 

Hulea IN, Brom HB, Mukherjee AK, Menon R (2005) Doping, density of states, and conductivity in polypyrrole and poly(p-phenylene vinylene). Phys Rev B 72 054208... 

Bruno FF, Nagarajan R, Roy S, Kumar J, Samuelson LA (2003) Biomimetic synthesis of water soluble conductive polypyrrole and poly(3,4-ethylenedioxythiophene). J Macromol Sci A Pure Appl Chem A 40(12) 1327-1333... 

R. Garjonyte and A. Malinauskas, Glucose biosensor based on glucose oxidase immobilized in electropolymerized polypyrrole and poly(o-phe-nylenediammine) films on a Prussian blue-modified electrode, Sens. Actuators B, 63 (2000) 122-128. 

Several conjugated polymers such as polyaniline, polypyrrole and poly thiophene have been prepared by chemical methods using doping. The electrical conductivity of these polymers has been controlled by (i) the type of dopant, (ii) the concentration of doping, (iii) the conditions of doping (the current density, temperature of reaction, etc.)... 

The case U = 0 is of special interest. In such a case, making one bipolaron from two polarons does not cost energy. The maximum spin concentration is i, which means that 50% of the boxes possess unpaired spins. This result can be explained as follows. Since (1) at the maximum spin concentration one has q = 1, and (2) placing one or two balls in the box is equivalent, there are four equiprobable cases (1) neutral site (no ball), (2) polaron up, (3) polaron down, and (4) bipolaron (two balls). Two among four of these states are magnetic, which gives for the spin concentration. The room-temperature data for polypyrrole and poly aniline can almost be fitted with U 0, which means that in these compounds polarons and bipolarons would be degenerate. 

In order to increase the selectivity and efficiency of extraction, novel stationary phases have been developed, particularly in trace analysis. Cyclodextrins, graphi-tized carbon blacks, and conductive polymers such as polypyrrole and poly aniline have been investigated [73]. Sol-gel polymers also seem to be interesting. A particularly important feature is the high thermal stability of these polymers [74]. Recent applications for analysis of biological samples have been described in several articles [75-81]. Review articles present recent developments in methodology, the SPME technique [82-84], and novel coatings [85, 86]. 

The template-assisted synthetic strategies outlined above produce micro- or mesoporous stmetures in which amorphous or crystalline polymers can form around the organic template ligands (174). Another approach is the use of restricted spaces (eg, pores of membranes, cavities in zeolites, etc.) which direct the formation of functional nanomaterials within thek cavities, resulting in the production of ultrasmaU particles (or dots) and one-dimensional stmetures (or wkes) (178). For example, in the case of polypyrrole and poly(3-methylthiophene), a solution of monomer is separated from a ferric salt polymerization agent by a Nucleopore membrane (linear cylindrical pores with diameter as small as 30 nm) (179—181). Nascent polymer chains adsorb on the pore walls, yielding a thin polymer film which thickens with time to eventually yield a completely filled pore. De-encapsulation by dissolving the membrane in yields wkes wherein the polymer chains in the narrowest fibrils are preferentially oriented parallel to the cjlinder axes of the fibrils. 

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). 

Alkyl aryl sulfides electrochemically oxidized on electrodes whose surfaces were modified by coating them with optically active compounds like camphoric acid [89] and poly(amino acids) [90, 91] afford mixtures of sulfoxides with variable enantiomeric excess. An optical yield of 93% is claimed when f-butyl phenyl sulfide is oxidized at a Pt electrode doubly coated with polypyrrole and poly(L-valine) [91]. 

All experiments showed that the corresponding polymers precipitated from solution. After filtration and washing with hot water, polypyrrole and poly(EDT) were obtained as dark powders in their oxidized state. Conductivity measurements showed that these materials have the same electrical properties (10-100 S cur1) as conventionally prepared polypyrrole or poly(EDT) [27,28],... 

S. Wencheng and O.I. Jude. Electrodeposition mechanism, adhesion and corrosion performance of polypyrrole and poly(N-methylpyrrole) coatings on steel substrates. Synth. Metals, 2000, Vol. 114, pp. 225-234. 

Hwang B. J., Yang J. Y., and Lin C. W., A Microscopic Gas-sensing model for Ethanol sensors based on conductive polymer composite from polypyrrole and poly(ethylene oxide), J. Electrochem. Soc. 146, 1231-1236, 1999. 

Conjugated polymers (particularly, polythiophene, polypyrrole, and poly-furan) and aromaticity 05CRV3448. 

H. Yamato, M. Ohwa, and W. Wernet, Stability of polypyrrole and poly(3,4-ethylenediox-ythiophene) for biosensor application, J. Electroanal. Chem., 397(1-2), 163-170 (1995). 

Kou, C.T., and T.R. Lion. 1996. Characterization of metal-oxide-semiconductor field-effect transistor (MOSFET) for polypyrrole and poly(N-alkylpyrrole)s prepared by electrochemical synthesis. Synth Met 82 167. 

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