Electrically active polymers polyacetylenes

Fig. 2.11. Three organic semiconducting polymers, (a) Polypyrrole, (b) plythipo-hene, and (c) poly(3,4-ethylenedioxythiophene) (PEDOT). All three have an sp conjugated backbone identical to polyacetylene. It is along the pi-bonds in this backbone that these materials exhibit carrier delocalization and electrical activity.

Most of the reported conjugated polymers with nonlinear optical or electrical activities are carbon-carbon conjugated systems, such as the extensively studied polyenes (e.g., polyacetylenes [15], polydiacetylenes [16,17], poly-/ -phenylenes) and heteroaromatic polymers (e.g., polypyrroles, polythiophenes, polycarbazoles, polyanilines) [18]. The synthetic methods, applications, and the structure-property relationships of these polymers have also been substantially investigated [19-21]. 

Polyacetylene has been the subject of intense research activity for many decades. A critical review of its history and evolution reveals that synthetic methods can be used to improve upon the processability of PA, albeit at a cost in the electrical conductivity. Although polyacetylene and its analogs exhibit a wide range of useful properties, none of these polymers are widely used in commercial applications. This observation suggests that the chemistry and physics of PA and PA analogs will continue to be a heavily researched topic for many more years to come. 

Conducting polymers such as polyacetylene, polypyrrole, polyaniline, polythiophene, etc. have been actively studied for use in various fields due to their interesting properties batteries,46 electrochromic displays,47 materials for supercapacitors,48 corrosion protection,49 protecting layers for static electricity,50 materials for organic electroluminescence displays,51 sensing materials,52 etc. Polypyrrole is reported to be extremely rigid, with a semi-crystalline structure. 

Since the seminal experiments in 1977 on polyacetylene ) showing that this polymer could be made electrically conductive upon doping, an intensive research activity has been unfold world-wide ). In the years following these first disclosures, polyacetylene has been studied in great detail, eventually leading to improved syntheses and a conductivity of 1.5 x 10 S/cm, which equals that of copper at room temperature ). 

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