Polypyrroles, properties chemical

A dramatic impact on chemical properties is achieved by the appropriate choice of counterion. The counterion employed during synthesis can have a marked effect on the anion-exchange selectivity series of conducting polymers.54 Table 3.4 shows the anion-exchange selectivity series obtained for both polypyrrole chloride and polypyrrole perchlorate. As illustrated, polypyrrole salts do not behave similar to conventional ion-exchange resins. 

Studies of the chemical properties of polythiophenes have been limited. As with polypyrroles, a hydrophobic backbone is formed, and the polymer has ion-exchange properties. Modification of chemical properties by incorporation of appropriate counterions is not so readily addressable because polymerization must be carried out from nonaqueous solution and occurs at more anodic potentials compared to pyrrole. 

In some cases, larger conducting polymer particles have been mixed with other polymers. For example, Bose and coworkers23 incorporated chemically synthesized polypyrrole (PPy) into PVC or nation. After casting, the materials were shown to be electroactive and demonstrated electrocatalytic properties. 

Maria Omastova and Ivan Chodak prepared conductive polypropylene/ polypyrrole composites using the method of chemically initiated oxidative modification of polypropylene particles in suspension by pyrrole. In order to prepare the composite, polypropylene particles were dispersed in water-methanol mixture and FeCb was added to be used for chemical oxidation. Addition of pyrrole started formation of polypyrrole particles in polypropylene suspension. The electrical and rheological properties of the composite were compared with polypropylene/polypyrrole composite prepared by melt mixing of pure polypropylene with chemically synthesized polypyrrole and with polypropylene/carbon black composites also prepared by melt mixing. Elemental analysis verified presence of polypyrrole in polypropylene matrix. The conductivity studies show that even a very small PPy amount present in composites results in a significant increase in... 

Kudoh, Y, K. Akami, and Y. Matsuya. 1998. Properties of chemically prepared polypyrrole with an aqueous solution containing Fe2(S04)3, a sulfonic surfactant and a phenol derivative. Synth Met 95 191. 

Pyrrole was first polymerized in 1916 [1,2] by the oxidation of pyrrole with H2O2 to give an amorphous powdery product known as pyrrole black. However, little further interest was shown in this material until it was electrochemically prepared in the form of continuous films. The electrochemical synthesis of polypyrrole dates to the early work of DalTOllio [3], who also obtained pyrrole blacks by electrochemical oxidation of pyrrole in aqueous sulfuric acid on a platinum electrode. In 1979 [4] electrochemical techniques to synthesize polypyrroles become a useful way to obtain highly conductive free-standing materials. Chemical and electrochemical methods of synthesis have since then been improved in order to optimize the physical and chemical properties of those materials. 

Other conducting polymers that have paying attention in composite preparation due to their remarkable physical and chemical properties are polypyrrole (PPy), polyvinylcarbazole (PNVCz), polythiophene (PTh), and their derivatives. 

Polymers being die most versatile and dynamic of all materials have a crucial role to play in tliis new area of science and technology. Obviously, even witliin this class of materials certain groups will emerge as being most appropriate. We believe conducting electroactive polymers (CEPs) is one of these groups of materials. Polymers such as polypyrroles (I), polythiophenes (II) and polyanilines (III) have unique properties that enable tlieir dynamic chemical properties to be studied, manipulated and controlled. 

The Monomer The chemical properties such as the ion exchange behaviour or die ability to undergo hydrophobic interactions arc influenced by die choice of the monomer. For example polyaniline has been shown to be less hydrophobic then polypyrrole (7,8). The electrochemical properties are also affected. Bodi... 

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

In considering the potential applications of electroactive polymers, the question always arises as to their stability. The deterioration of a physical property such as conductivity can be easily measured, but the chemical processes underlying it are not as easy to be revealed. In order to understand them, XPS has been used to follow the structural changes which occur in the polymer chain and the counter-ions of the doped polymer. The following sections present some XPS findings on the degradation of electroactive polymers, such as polyacetylene, polypyrrole, polythiophene and polyaniline, in the undoped and doped states. 

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]. 

It has been mentioned already that polypyrrole (25) and polythiophene (26) play an important role as electrical conductors and polymeric anodes in battery cells [2,47,226]. Since the charging and discharging of the conjugated polymer is accompanied by the incorporation and removal of counterions it is clear that the material can also act as a carrier of chemically different anions which influence the physical, chemical and physiological properties of the material [292]. With regard to the full structural elucidation of the polymers it must be added, however, that the electropolymerization process of pyrrole and thiophene does not provide a clean coupling of the heterocycles in the 2,5-positions. Instead, the 3- and 4-position can also be involved giving rise to further fusion processes under formation of complex polycyclic structures [47]. 

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