Intercalation polyacetylene

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. 

Organic compounds like polyacetylene are another example of this class of intercalation compound, as discussed in Chapter 5. 

Five aspects of the preparation of solids can be distinguished (i) preparation of a series of compounds in order to investigate a specific property, as exemplified by a series of perovskite oxides to examine their electrical properties or by a series of spinel ferrites to screen their magnetic properties (ii) preparation of unknown members of a structurally related class of solids to extend (or extrapolate) structure-property relations, as exemplified by the synthesis of layered chalcogenides and their intercalates or derivatives of TTF-TCNQ to study their superconductivity (iii) synthesis of a new class of compounds (e.g. sialons, (Si, Al)3(0, N)4, or doped polyacetylenes), with novel structural properties (iv) preparation of known solids of prescribed specifications (crystallinity, shape, purity, etc.) as in the case of crystals of Si, III-V compounds and... 

The first experiments were carried out on films of solid CeO) 100 to 1000 A thick, exposed to alkali metal vapors.[Ha91a ] It was observed that the conductivity increased by more than seven orders of magnitude, to 500 (fl cm) . This is still a much lower conductivity than any metallic element, but on the order of such organic systems as doped polyacetylene. Haddon et al. made the plausible suggestion, subsequently proved, that the smaller alkali ions were intercalated into the voids between the much larger fullerenes, and donated their charge to the unoccupied fullerene molecular orbital. The ratio of alkali atoms to fuUerenes in the (super) conducting phase was not then known, nor was it known whether the structure was based on the... 

The dopant ions are very large and the polyacetylene crystallites arc strongly disrupted structures are less ordered than in the case of I2 or even Sbp5 doping. Vapour doping apparently results in better lateral order, in spite of a possible intercalation of the neutral species [147]. In every case, the doped material behaves as an inhomogeneous mixture of undoped and doped poly-... 

Some of the results obtained over the years are collected in Tables 1.5 and 1.6. The first of these lists the value of the intercalation period, the second the meridional repeat distance of the ion sublattice (along the chain axis). More reflections have been observed to result from doping, notably at 3.3-3.4 A and at 4.5-4.7 A. The values of the c-repeat of the ion sublatticc show considerable variation, but those obtained from highly oriented polyacetylene are more reliable [102,138,147]... 

The dopant molecules may furthermore enter the hose lattice in an organized fashion, giving rise to new, enlarged repeating units and corresponding new reflection peaks in the diffraction patterns. Ordered intercalation is a well known phenomenon for graphite compounds (see for instance [113]) and has also been observed for dopants in polyacetylene [114]. In the present section we shall discuss the actual situation for polythiophenes. 

Polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, and poly-methylthiophene may exhibit a mixed electronic and ionic conductivity, similar to inorganic intercalation, or insertion compounds [43]. In the conductive form these polymers are partly oxidized and these positive charges are equilibrated by inorganic anions, which can diffuse through the polymer net. Alternatively, the conductive polymers can be partly reduced, with cations as counter ions. The eleetronic conductivity originates Irom partial oxidation of conjugated jt-bonds. The positive charge... 

Doping may impose further structural effects that depend on the size and nature of the dopant species. Although there may still not be complete accord on the crystal structure of lithium-doped polyacetylene, it appears that at low doping levels entropic factors are important in inserting a small nonaggregating ion, such as Li", into polyacetylene (PAc), with the dopant occupying sites with minimal strain or disruption of the host lattice. Iodine, on the other hand, in the form of IJ and IJ (and possibly higher polyiodides), produces structures in which anions cluster in columns or sheets to form intercalated layers between polymer chains. ... 

Flandrois, S., C. Hauw, and B. Francois. 1983. Analogies between graphite intercalation compounds and doped polyacetylene. J Phys (Paris) 44 C3. 

Fig. 5 shows the dependence of the integrated net intensity of the "intercalation" peak from the polyacetylene iodine complex compound at 2 10.4 on the iodine content. A linear relationship is obtained. Note that there is a threshold-value of iodine content at y=2.3 percent I/CH. Below this level an intercalation peak is not formed but the background intensity increases from the initial product up to this level due to iodine absorbed and/6r reacted at the surface of the sample. The specific surface area of such free standing sheets of poly(acetylene) is of the order of lOOm g". ... 

The intercalation of lithium into a suitable material. These include TiS, V O 3, Mn02 M0S2 and certain neutral polymers such as polyacetylene. In an intercalation reaction, the lithium passes into the lattice and it may be written ... 

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