Polyacetylene morphology

Thus a number of contrasts exist between poly-1,6 and polyacetylene morphology, crystallinity, undoubtedly molecular... 

The fibrillar morphology of Shirakawa polyacetylene is an advantage in applications requiring a high surface area but a problem in many other cases, especially the study of diffusion and transport processes and the possible device applications where re-... 

As prepared by the method of Shirakawa et al. 2 3), polyacetylene is a free-standing film. On closer examination, its density is found to be around 0.4gem-3, only about 30% of the value (1.16 gem-3) predicted from X-ray analysis, and electron microscopy reveals complex morphologies. 

The materials used in most current research are irregular mats of highly crystalline fibrils with diameters of around 10 nm, so that the films are characterised by a very high surface area (around 60 m2 g-1), a problem in some potential applications and an asset in others. The morphology of polyacetylene is sensitive to the conditions of preparation and to ageing and was the subject of much heated discussion in the early development of polyacetylene. 

The same authors 369,3701 also obtained similar results if the liquid crystal solvent was aligned by flow during the polymerization. They showed that the polymerization conditions lead to alignment of the fibrils within the polymer mass and of the chains within the fibrils polymers produced in this way could also be doped to a conductivity of 104 S cm-1 371). The morphology of polyacetylene produced by polymerization in a liquid crystal solvent, aligned both magnetically and by flow, has been studied by Montaner et al. 371). They show that the polymer film is made up of very long fibrils built from microfibrils. In one fibril, the orientation of microcrystalline domains with respect to the fibril axis is very well defined, whilst the orientation of the different fibrils in the sample spreads over 20°. 

The diffusion behaviour of Shirakawa polyacetylene is complicated by its fibrillar morphology and high surface area, so that weight changes depend on pore transport and surface adsorption, as well as on diffusion into the fibrils. Chien 6) has reviewed earlier studies of the diffusion of dopant counter-ions in Shirakawa polymer and has emphasised the wide range of values of diffusion coefficient which are reported and which depend a great deal upon the morphological model chosen to interpret experimental data. 

Durham polyacetylene has the advantage of being a uniform, dense film and so lends itself much more readiliy to diffusion studies. In addition, the uniform morphology is much better suited to device applications, although the low surface area would limit applications in batteries. We have made extensive measurements on the doping of Durham frans-polyacetylene by gaseous AsF5 514 515), which is believed to dope the polymer to form the hexafluoroarsenate ion and arsenic trifluoride 516 ... 

Unsubstituted polyacetylene, like many other conductive polymers, is an intractable material and thus its processing into useful shapes and morphologies is limited. One solution to the processing problems has been the use of soluble precursor polymers that can be transformed into conductive polymers. Application of ROMP in the formation of soluble polyacetylene precursors was elegantly pioneered by Feast and coworkers [61]. Using this approach, a precursor polymer is synthesized by the ROMP of a cyclobutene derivative. Once synthesized, the precursor polymer can undergo a thermally promoted, retro-Diels Alder reaction to split off an aromatic fragment and produce polyacetylene, Eq. (42). 

The problem of the nature of the conducting state in polyacetylene cannot be considered without a close investigation of the real nature of the samples, including characteristics such as morphology, crystallinity, defect concentration, chain length, and so on. In the early 1980s the studies were concerned with (CH) obtained by the Shirakawa method. The doping level y appeared to be a crucial parameter. As a function of y, basically... 

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