Electron-exchange polymers examples

An enormous number of polymers have been used to prepare chemically modified electrodes. Some examples are given in Table 13.2 Albery and Hillman provide a more extensive list [8]. As indicated in Table 13.2, these polymers can be divided into three general categories—redox polymers, ion-exchange and coordination polymers, and electronically conductive polymers. Redox polymers are polymers that contain electroactive functionalities either within the main polymer chain or in side groups pendant to this chain. The quintessential example is poly(vinylferrocene) (Table 13.2). The ferrocene groups attached to the polymer chain are the electroactive functionality. If fer-... 

Specificity can also be controlled to some extent by the introduction of electrocatalytic properties in the polymer. For example, the incorporation of Fe(CN)6 as a counterion [43] or the use of a Prussian Blue coating on a conducting polymer inner layer [44] can promote electron exchange with Cytochrome C. 

Electroactive polymers can be divided into three broad classes electronically conducting polymers, such as poly(pyrrole), in which conduction is associated with motion of charge carriers along the chains redox polymers, such as poly(vinylfer-rocene), in which conduction is associated with cross-exchange reactions between discrete redox sites and polymer electrolytes, such as Nafion, in which conduction is associated with ion motions within the film. Examples of polymers from all three classes have been used in bioelectrochemical applications. 

The need for high electronic conductivity has meant that work has focused on the use of the so called conducting polymers, exemplified by polypyrrole, polyaniline and polythiophene (Structures 1 to 3). These materials must be in their p-doped (partially oxidized) states (right hand side of eq. 1, for example) to exhibit sufficient electronic conductivity. Unfortunately, the p-doped polymers are cationic and will therefore tend to exclude the protons needed for the fuel cell reactions. To circumvent this problem, composites of conducting polymers with cation exchange polymers have been used. Thus p-doped polypyrrole / poly(styrene-4-sulphonate) (PSS), for example, exhibits both proton and electron conductivity (8). 

Even in cases where the redox sites are immobilized by chemical bonding to the matrix, they will still have a certain local mobility. One can therefore describe the electron transport by assuming that electron exchange between the redox sites does not take place over the distance A, as assumed above, but that the donor and acceptor sites come into intimate contact for electron transfer [26,207]. This mechanism was proposed to be operative, for example, with iron redox sites embedded in a plasma polymer matrix [26]. 

The size-exclusion and ion-exchange properties of zeoHtes have been exploited to cause electroactive species to align at a zeoHte—water interface (233—235). The zeoHte thus acts as a template for the self-organization of electron transfer (ET) chains that may find function as biomimetic photosynthetic systems, current rectifiers, and photodiodes. An example is the three subunit ET chain comprising Fe(CN)g anion (which is charge-excluded from the anionic zeoHte pore stmcture), Os(bipyridine)3 (which is an interfacial cation due to size exclusion of the bipyridine ligand), and an intrazeoHte cation (trimethylamino)methylferrocene (F J ). A cationic polymer bound to the (CN) anion holds the self-assembled stmcture at an... 

We have already seen that photoactive clusters, e.g. CdS, can be introduced into vesicles and BLMs (Sect. 5.2 and 5.3). Similar support interactions are possible with both inorganic and organic polymeric supports. Photoactive colloidal semiconductor clusters can be introduced, for example, into cellulose [164], porous Vycor [165], zeolites [166], or ion exchange resins [167]. The polymer matrix can thus influence the efficiencies of photoinduced electron transfer by controlling access to the included photocatalyst or by limiting the size of the catalytic particle in parallel to the effects observed in polymerized vesicles. As in bilayer systems,... 

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