Electrochemical polymerization, selective

The electrochemical polymerization process is achieved by polymerization of monomers in an electrolytic cell (Subramanian and Jakubowski, 1978). The electrode is the source of active species that initiates the polymerization. It is necessary to select a solvent electrolyte system which is capable of forming a solution with the monomer and having sufficient current-conducting properties. In the process employed by Bell and coworkers (Bell et al., 1987 Wimolkiatisak and... 

Asymmetric synthesis selective electrolysis electrochemical polymerization... 

In situ polymerization, and electrochemical polymerization in particular [22], is an elegant procedure to form an ultra thin MIP film directly on the transducer surface. Electrochemical polymerization involves redox monomers that can be polymerized under galvanostatic, potentiostatic or potentiodynamic conditions that allow control of the properties of the MIP film being prepared. That is, the polymer thickness and its porosity can easily be adjusted with the amount of charge transferred as well as by selection of solvent and counter ions of suitable sizes, respectively. Except for template removal, this polymerization does not require any further film treatment and, in fact, the film can be applied directly. Formation of an ultrathin film of MIP is one of the attractive ways of chemosensor fabrication that avoids introduction of an excessive diffusion barrier for the analyte, thus improving chemosensor performance. This type of MIP is used to fabricate not only electrochemical [114] but also optical [59] and PZ [28] chemosensors. 

Polypyrrole thin film doped with glucose oxidase (PPy-GOD) has been prepared on a glassy carbon electrode by the electrochemical polymerization of the pyrrole monomer in the solution of glucose oxidase enzyme in the absence of other supporting electrolytes. The cyclic voltammetry of the PPy-GOD film electrode shows electrochemical activity which is mainly due to the redox reaction of the PPy in the film. Both in situ Raman and in situ UV-visible spectroscopic results also show the formation of the PPy film, which can be oxidized and reduced by the application of the redox potential. A good catalytic response to the glucose and an electrochemical selectivity to some hydrophilic pharmaceutical drugs are seen at the PPy-GOD film electrode. 

In this paper we report the electrochemical polymerization of the PPy-GOD film on the glassy carbon (GC) electrode in enzyme solution without other supporting electrolytes and the electrochemical behavior of the synthesized PPy-GOD film electrode. Because the GOD enzyme molecules were doped into the polymer, the film electrode showed a different cyclic voltammetric behavior from that of a polypyrrole film doped with small anions. The film electrode has a good catalytic behavior to glucose, which is dependent on the film thickness and pH. The interesting result observed is that the thin PPy-GOD film electrode shows selectivity to some hydrophilic pharmaceutical drugs which may result in a new analytical application of the enzyme electrode. 

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. 

Another way to functionalize depositions, is to entrap functional molecules in polypyrrole. Incorporation of functional molecules during electrochemical polymerization and the application of so prepared films to sensors have been studied by many workers (27). By means of area-selective deposition much more complicated functional depositions can be prepared on an electrode. The authors have shown that organic dyes (an example of functional molecules) are incorporated in the process of... 

Similar to photolithography, subsequent processing steps are required to define features. For this reason, j,CP is also typically limited to the fabrication of electrodes in bottom-contact OTFTs. The subsequent processing steps can be classified into three categories selective etching [29,33-35], selective electroless plating [36-39], and selective chemical and electrochemical polymerization [40-43]. Depending on... 

Completely different monomers were called for. Before long, three of today s workhorses had been identified pyrrole, aniline and thiophene. In Japan, Yamamoto [38] and in Germany, Kossmehl [39] synthesized polythiophene doped with pentafluoroarsenate. At the same time, the possibilities of electrochemical polymerization were recognized. At the IBM Lab in San Jose, Diaz used oxidative electrochemical polymerization to prepare polypyrrole [40] and polyaniline. [41] Electrochemical synthesis forms the polymer in its doped state, with the counter-ion (usually an anion) incorporated from the electrolyte. This mechanism permits the selection of a wider range of anions, including those which are not amenable to vapor-phase processes, such as perchlorate and tetra-fluoroborate. Electrochemical doping also overcomes an issue associated with dopants... 

The polypyrrole-glycose oxidase combination is the one that has been investigated most extensively [61,62,63]. The selective layer is prepared by electrochemical polymerization of the monomer in the presence of the enzyme. The retention is believed to be affected by the entrapment. 

Conductive polymer films on electrodes have been prepared by electrochemical polymerization of electroactive monomers such as a pyrrole-substituted mediator, or by evaporating solutions containing preformed polymer. Examples of electrocatalyses reported include the oxidation of alcohols by pyrrole-substituted 2,2,5,5-tetramethyl-3-pyrroline-l-oxyl [26] and organohalide de-halogenation by pyrrole-substituted 4,4 -bipyridinium salt [27]. The preparation of mediator-modified electrode by evaporating solutions of preformed polymers was carried out by dip-coating polymers including mediators on electrode surface or by covalent attachment of mediators to dip-coated polymers on electrode surfaces. Examples of the former electrocatalyses are selected from the several reports on the oxidation of NADH by dopamine... 

Once the coexistence of different processes during electropolymerization is detected, the final composition and properties of the electrogenerated polypyrroles can be related to the chosen parameters of synthesis. The reverse reasoning is always true and fundamental from a technological point of view on defining a property, specific conditions of synthesis can be selected in order to optimize it. As the electrochemical polymerization of pyrrole involves many experimental variables, adequate control of the polymer synthesis will require analysis of the effects of the individual parameters (electrode, solvent, electrolyte, pH of the solution, temperature, and potential of synthesis) and their interdependence. 

Because crown ethers have more effective and selective cation binding properties than linear polymers, electrochemical polymerization of 43 was performed [246] and a new electroactive conducting material was obtained however, its structure was not determined. 

Preliminary work by Schiavon et al. [226] and a follow-up study by Zotti and Schiavon [113] undertook the electrochemical polymerization of dihydrobenzodi-pyrroles in acetonitrile. Selected monomers used for the polymerizations are pictured in Fig. 11. The anodic coupling of three different isomers of dihydrobenzo-dipyrroles in 0.1 M tetraethylammonium perchlorate in acetonitrile produced films. These films could be reversibly oxidized at 0.3 V (versus Ag/Ag ) with 0.5 electron per monomer unit. The electrochemically synthesized films were believed to be more ordered than chemically prepared samples, as indicated by their differences in conductivity. Conductivities of 0.2 to 5 S cm were recorded for electrochemically synthesized films compared to conductivities of lO " to 10 S cm for comparably chemically produced films. 

This report describes some of the recent work on the electrochemical and electrode applications of polymers which are electroactive and can be switched to an electrically conductive state, as well as the inherently conductive (SN. The materials fall into two general categories. There are the polymer tllms which can be prepared in situ by the electrochemical polymerization of aromatic compounds, and there are the polyenes such as polyacetylene and polythiazyl. Many of the electrode applications being considered are based on the. electroactive/conductive properties of the films such as display devices, and storage batteries. Some applications make use of the conductive property of the materials such as protective coatings against corrosion, and other applications make use of the possibility for molecular selectivity such as chemically selective electrodes and sensors. 

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