Redox Reactions polyacetylene

Polymers. Electronically conductive polymers may also be used as cathode materials in rechargeable lithium batteries. The most popular polymers are polyacetylene, polypyrrole, polyaniline, and polythiophene, which are made conductive by doping with suitable anions. The discharge-charge process is a redox reaction in the polymer. The low specific energy, high cost, and their instability, however, make these polymers less attractive. They have been used in small coin-type batteries with a lithium-aluminum alloy as the anode. 

The mechanism for the polymerisation of acetylene is inherently different from that of aromatic monomers such as pyrrole or thiophene. Whereas the polymerisation of pyrrole or thiophene involves a redox reaction,(77,74) the corresponding reaction of acetylene is probably initiated by acidic properties of the catalyst.(22) In the case of polyacetylene evidence has been obtained to suggest that the nature of the cations in the zeolite lattice is also important.(75) Fig. 1 shows a series of Raman spectra which illustrate the influence of various cations upon the extent of polymerisation, demonstrate the effect of elevating the acetylene pressure and indicate a role for Lewis acid sites in the reaction mechanism. Exposure of acetylene (0.1 MPa) to sodium-mordenite (NaM) at 295 K gave the spectrum displayed in Fig. 1(a). Bands at 398 and 468 cm are ascribed to lattice modes of the mordenite structure(2J), whereas the peak at ca. 1958 cm can be attributed to the Vj vibration of adsorbed monomeric acetylene bound in a side-on" manner to cation sites (16,23). Relatively small maxima at 1112 and 1502 cm are characteristic of trans-polyacetylene (5,18,24,25). Exchange of cesium for the sodium ions in mordenite was found to be beneficial for the formation of polyacetylene, as can be seen in Fig. 1 (b). In addition to the noted intensification of bands typical of rra/iy-polyacetylene at 1112 and... 

The concept of electrochemical intercalation/insertion of guest ions into the host material is further used in connection with redox processes in electronically conductive polymers (polyacetylene, polypyrrole, etc., see below). The product of the electrochemical insertion reaction should also be an electrical conductor. The latter condition is sometimes by-passed, in systems where the non-conducting host material (e.g. fluorographite) is finely mixed with a conductive binder. All the mentioned host materials (graphite, oxides, sulphides, polymers, fluorographite) are studied as prospective cathodic materials for Li batteries. 

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