Poly-alcohols pyrrole

Vinyl polymers such as poly(vinyl alcohol) (PVA) and poly(vinyl pyrrol-idone) (PVP) [42,44,57-62] ... 

In recent years further concepts have been developed for the construction of polymer-based diodes, requiring either two conjugated polymers (PA and poly(A-methyl-pyrrole) 2 > or poly(A-methylpyrrole in a p-type silicon wafer solid-state field-effect transistor By modifying the transistor switching, these electronic devices can also be employed as pH-sensitive chemical sensors or as hydrogen or oxygen sensors 221) in aqueous solutions. Recently a PPy alcohol sensor has also been reported 222). 

Several approaches have been undertaken to construct redox active polymermodified electrodes containing such rhodium complexes as mediators. Beley [70] and Cosnier [71] used the electropolymerization of pyrrole-linked rhodium complexes for their fixation at the electrode surface. An effective system for the formation of 1,4-NADH from NAD+ applied a poly-Rh(terpy-py)2 + (terpy = terpyridine py = pyrrole) modified reticulated vitreous carbon electrode [70]. In the presence of liver alcohol dehydrogenase as production enzyme, cyclohexanone was transformed to cyclohexanol with a turnover number of 113 in 31 h. However, the current efficiency was rather small. The films which are obtained by electropolymerization of the pyrrole-linked rhodium complexes do not swell. Therefore, the reaction between the substrate, for example NAD+, and the reduced redox catalyst mostly takes place at the film/solution interface. To obtain a water-swellable film, which allows the easy penetration of the substrate into the film and thus renders the reaction layer larger, we used a different approach. Water-soluble copolymers of substituted vinylbipyridine rhodium complexes with N-vinylpyrrolidone, like 11 and 12, were synthesized chemically and then fixed to the surface of a graphite electrode by /-irradiation. The polymer films obtained swell very well in aqueous... 

The HOPG (highly oriented pyrolytic graphite) carbon electrode chemically modified with (5[-phenylalanine at the basal surface led to 2% ee in the reduction of 4-acetylpyridine [377]. A cathode modified with a chiral poly(pyrrole) reduced 4-methylbenzophenone or acetophenone in DMF/LiBr and phenol as proton donor to 1-phenylethanol with up to 17% ee [382]. Alkyl aryl ketones have been reduced to the corresponding alcohols at a Hg cathode in DMF/water in the presence of (1R,2S)-A,A-dimethylephedrinium tetrafluorobo-rate (DET), producing (5 )-l-phenylethanol with 55% ee from acetophenone. Cyclovoltammetry supports an enantioselective protonation of the intermediate (PhCOH(CH3)) [383]. 

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). 

Polyelectrolytes and soluble polymers containing triarylamine monomers have been applied successfully for the indirect electrochemical oxidation of benzylic alcohols to the benzaldehydes. With the triarylamine polyelectrolyte systems, no additional supporting electrolyte was necessary [91]. Polymer-coated electrodes containing triarylamine redox centers have also been generated either by coating of the electrode with poly(4-vinyltri-arylamine) films [92], or by electrochemical polymerization of 4-vinyl- or 4-(l-hydroxy-ethyl) triarylamines [93], or pyrrol- or aniline-linked triarylamines [94], Triarylamine radical cations are also suitable to induce pericyclic reactions via olefin radical cations in the form of an electron-transfer chain reaction. These include radical cation cycloadditions [95], dioxetane [96] and endoperoxide formation [97], and cycloreversion reactions [98]. 

Poly(pyrrole)-poly(vinyl alcohol) composite films which are conducting and transparent [202]. 

Coral-hke nanowires and nanowire networks of conducting PPy have been synthesized by chemical oxidation polymerization of pyrrole monomers in a dodecyl-benzene sulfonic acid (DBSA) aqueous solution with FeCla as oxidant and poly(vinyl-alcohol) (PVA) as... 

Ramanavicius, A., K. Habermuller, E. Csoregi, V. Laurinavicius, and W. Schuhmann. 1999. Poly-pyrrole-entraped quinohemoprotein alcohol dehydrogenase. Evidence for direct electron transfer via conducting-polymer chains. Anal Chem 71 3581. 

The use of polymeric blend composites for corrosion protection of AA 2024-T3 has been reported, including composites formed by incorporating water-soluble conducting polymers (either polymethox-yaniline sulfonic acid or poly(4-(3-pyrrole) )butane sulfonate) into various binders (a cross-linked polyvinyl alcohol, a waterborne epoxy, a modified water-dispersible polyester, and a UV-curable urethane acrylate binder) [149]. The preparation of epoxy and polyaniline composite coatings has been described, using either nanodispersed EB particles [91] or EB that was first dissolved in selected amine hardeners before adding the epoxy resin [98]. Even with very low EB loadings, these workers reported enhanced corrosion protection for steel. 

The second approach for improving the processabihty of ICPs is to prepare their colloidal dispersions in water or an appropriate solvent The colloid dispersions of ICPs can be obtained by chemical or electrochemical oxidation of the monomer in the presence of a steric stabihzer [29-31].The key parameter for such synthesis is the choice of an appropriate steric stabihzer which adsorbs or grafts onto the polymer coUoidal particles to prevent their aggregation or precipitation. Several polymers such as polyfethylene oxide) [32], poly(vinyl pyrroHdone) [33,34], poly(vinyl alcohol) [35], ethyl hydroxy cellulose [36], poly(vinyl alcohol-co-acetate) [37], poly(vinyl methyl ether) [38,39] and block copolymer stabihzer [40] have been used as steric stabihzers to produce PPy coUoidal dispersions. Surfactants are also employed for the synthesis of ICP coUoidal dispersions [41,42]. Very recently, stable PPy dispersions were prepared by Lu et al. by polymerizing pyrrole in an aqueous medium containing different anionic salts such as sodium benzoate, potassium hydrogen phthalate, and sodium succinate [43]. These authors also reported that the conductivity of PPy dispersions was enhanced when sodium benzoate was used as dopant. Chemical oxidahve polymerization in the presence of PSS in aqueous medium produces coUoidal dispersions and improves processability [44]. CoUoidal dispersions... 

Electrical properties have been reported on numerous carbon fiber-reinforced polymers, including carbon nanoflber-modified thermotropic liquid crystalline polymers [53], low-density polyethylene [54], ethylene vinyl acetate [55], wire coating varnishes [56], polydimethyl siloxane polypyrrole composites [50], polyacrylonitrile [59], polycarbonate [58], polyacrylonitrile-polycarbonate composites [58], modified chrome polymers [59], lithium trifluoromethane sulfonamide-doped polystyrene-block copolymer [60], boron-containing polyvinyl alcohols [71], lanthanum tetrafluoride complexed ethylene oxide [151, 72, 73], polycarbonate-acrylonitrile diene [44], polyethylene deoxythiophe-nel, blends of polystyrene sulfonate, polyvinyl chloride and polyethylene oxide [43], poly-pyrrole [61], polypyrrole-polypropylene-montmorillonite composites [62], polydimethyl siloxane-polypyrrole composites [63], polyaniline [46], epoxy resin-polyaniline dodecyl benzene sulfonic acid blends [64], and polyaniline-polyamide 6 composites [49]. 

Another widely used approach is the in situ polymerization of an intractable polymer such as polypyrrole onto a polymer matrix with some degree of processibil-ity. Bjorklund [30] reported the formation of polypyrrole on methylcellulose and studied the kinetics of the in situ polymerization. Likewise, Gregory et al. [31] reported that conductive fabrics can be prepared by the in situ polymerization of either pyrrole or aniline onto textile substrates. The fabrics obtained by this process maintain the mechanical properties of the substrate and have reasonable surface conductivities. In situ polymerization of acetylene within swollen matrices such as polyethylene, polybutadiene, block copolymers of styrene and diene, and ethylene-propylene-diene terpolymers have also been investigated [32,33]. For example, when a stretched polyacetylene-polybutadiene composite prepared by this approach was iodine-doped, it had a conductivity of around 575 S/cm and excellent environmental stability due to the encapsulation of the ICP [34]. Likewise, composites of polypyrrole and polythiophene prepared by in situ polymerization in matrices such as poly(vinyl chloride), poly(vinyl alcohol), poly(vinylidine chloride-( o-trifluoroethylene), and brominated poly(vi-nyl carbazole) have also been reported. The conductivity of these composites can reach up to 60 S/cm when they are doped with appropriate species [10]. 

A completely different approach to patterning conducting polymers involves the use of photosensitive oxidants [86,87]. In this process, a photosensitive oxidant is mixed with a host polymer such as poly (vinyl chloride), poly(vinyl alcohol), or polycarbonate. The composite is applied to a substrate. Upon irradiation of the film, the oxidant in the exposed regions is made inactive, whereas in the unexposed regions the oxidant can still induce polymerization of appropriate monomers. After exposure, the latent image is exposed to a monomer such as pyrrole either in solution or in the vapor state. Polymerization occurs only in the nonexposed areas where the oxidant is still active. In this fashion, patterns are delineated that consist of conducting composite materials. Some photosensitive oxidants include Fe(III) salts such as iron trichloride and ferrioxalate. Upon exposure, the Fe(III) is converted to Fe(II), which does not induce oxidative polymerization [86,87]. 

Ferric chloride Pyrrole vapor Water Polyamide, polyester, poly(vinyl alcohol) 1986 31... 

Open circles show the conductivity of prepared Poly(pyrrole) when the oxidation potential of the solutions was controlled by changing solvents. When the oxidation potential of methanol solutions was controlled by adding FeCl2 at the initial stage, the conductivity of the prepared Poly(pyrrole) is shown by the filled circles. (1) DMA, (2) DMP, (3) Ethylene Glycol, (4) Me-OH, (5) Et-OH, (6) Water, (7) Pentanol, (8) Octyl Alcohol, (9) 0.7M Fe(C104)3, (10) Benzene, (11) Acetone, (12) Acetonitrile, and (13) Chloroform. After Reference [80], reproduced with permission. 

An oxidant-sorption procedure was used by Ojio and Miyata [338] for the fabrication of P(Py)/PVA (Poly(Vinyl Alcohol)) composites. PVA, of M 22,000, was dissolved with FeClj (the oxidant) in water, a film cast from this solution onto a PET film substrate. This oxidant-saturated host-polymer film was then exposed, in a desiccator at low temperature and in a deoxygenated atmosphere, to monomer (pyrrole) and water vapor for 0.5 to 24 h, with the resulting composite films, ca. 2 jam thick, dried in vacuum. Conductivities and transmission values saturated at about 1 h exposure time, to ca. 1 S/cm and 40% ( 550 nm) for a 70 30 w/w ratio PVA/FeClj. Transmission of the film was down to ca. 55% within 0.5 h, (with conductivity ca. 0.1 S/cm) for the same PVA/FeClj ratio. Higher PVA/FeClj ratios (90 10, 95 5) gave not only higher transmissions with minimal conductivity reduction, but also more homogeneous films as evidenced by SEM. 

As moitioned b ie, composites can be prepared electrochemically, typically by polymerizing the monomer on an electrode that had been pretreat with a pol)rmer. This process has beat performed with pyrrole using (with a variety of modifications as well) poly(vinyl alcohol), pol)Kvinyl diloride), polyurethane, and as a graft onto polystyrene functionalized with benzyl chloride side- ains. Pyrrole has been mixed with Kevlar (an ultra high modulus polymer) and chemically polymerized to form a very strong "alloy" fiber of polypyrrole and Kevlar. s... 

Polymer-modified electrodes can be prepared either by direct deposition of polymer onto the surface (via drop-, dip- or spin-coating methods) or by polymerization onto the electrode surface (via chemical, electrochemical or photochemical routes). The simplest method to prepare a polymer-based sensor is by drop-coating a small volume of polymer dissolved in a solvent. With time, the solvent evaporates leaving the polymer adsorbed onto the electrode surface. Dip- and spin-coating methods have also been used to obtain more uniform films. These methods are used when polymers are aheady synthesized and need to be immobilized as they are. In situ polymerization is another effective method to prepare polymer-modified electrodes. For electropolymerization, the electrode is immersed in a monomer solution (e.g., pyrrole, thiophene, phenol, aniline...) and a suitable potential (either cathodic or anodic) is applied to allow the formation of the polymer film on the electrode surface. Photopolymerization is rarer in the case of electrochemical sensors. Nevertheless, poly(vinyl alcohol) functionalized with styrylpyridinium and acrylated polyurethane have been used for the development of electrochemical sensors. 

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