Durham polyacetylene doping

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 ... 

In our own work on Durham polyacetylene 568) wfe find that the stability of doped polymers depends upon the extent of doping. Thus when AsF6 is the counter-ion, a polymer doped to low levels (< 1 mol %) shows very little change in conductivity over a period of days at room temperature in vacuum or dry air, whereas saturation doping (to about 17 mol%) produces a polymer whose conductivity decays rapidly, with ir evidence for the formation of C—F bonds in the polymer. 

The first experimental data show that the tetragonal lattice is not realized for lithium [89]. This can be explained by means of packing calculations. The Li ion is much smaller than the holes in the most closely packed form of the lattice proposed (see Table 1.3 and Figure 1.9). Na is only slightly smaller, K just fits nicely, while Rb and Cs" ions leads to some expansion. Though Li-doped polyacetylene has been called amorphous at first, Leitner et al [95] demonstrate diffraction from Li-doped Durham polyacetylene. A number of possibilities for the location of the lithium ions is considered, based on a unit cell almost undistorted by doping [96]. 

One of the earliest examples of a conjugated polymer electronic device used transpolyacetylene which had been prepared by the Durham route. Precursor polyma- 2 has very good film-forming properties, and it is simple to control the thickness of the final polyacetylene film. Durham polyacetylene has electrical characteristics that are well suited to device fabrication. The carrier concentration (of the order 10 cm-s) results from unintentional doping, most likely from immobile catalyst residues that are chemically bound to the polymer chain ends. The undoped polymer can take over the role of the semiconductor in a metal-insulator-semiconductor field-effect transistor (MISFET). ... 

The effects of disorder in the unoriented Durham polyacetylene are also manifested in the transport properties, and we review here the picture that has been obtained for the transport mechanisms in the semiconducting (low carrier concentration) regime. Polyacetylene prepared by all routes shows a conductivity as prepared (i.e. not intentionally doped) that is due to extrinsic carriers which are p-type. There are several possible sources for the doping which creates these carriers, and we identify doping with... 

A triumph of the Durham route was the preparation of oriented crystalline polyacetylene (107-109) by stretch orientation of the polymer during the transformation reaction. This material has highly anisotropic optical properties, but the anisotropy of the conductivity of the doped polymer was low. Oriented fibers as well as films were prepared. 

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