Polyacetylenes, trans isomeric

The cis/trans isomerization of cw-polyacetylene, previously only disclosed from spectroscopic data, has recently been detected by cyclic voltammetry The analysis of the redox data reveals that the trans-form is thermodynamically more favorable in the charged than in neutral state. 

Figure 1. TYie trans isomeric form of polyacetylene shovn in its planar trans and cis conformations, with pertinent si )stituents numbered.

Fig. 57 a and b. Change of the diffraction pattern of cis-polyacetylene upon heating from room temperature with 11 °C min" The cis/trans isomerization is indicated by the disappearance of the 201 reflection at about 150 °C. Above about 290 °C a broad peak indicates decomposition... 

Fig. 24. Change of the wide-angle diffraction pattern of cw-polyacetylene during heating from room temperature with 11 °C/min. The disappearance of the (201) reflection at 150 °C indicates the cis/ trans isomerization, the broad peak above 290 °C indicates thermal degradation...

The soluble poly(RCOT)s undergo a photochemical cis/trans isomerization in solution - a reaction that is not observed for unsubstituted polyacetylene in the solid state. The photochemical cis/trans isomerization of poly(trimethylsilylCOT) can be followed by visible spectroscopy (Fig. 10-26) [124], Here, the chromophore is a collection of double bonds with an ef-... 

Thermogravimetric curves for the polyacetylene, there are two exothermic peaks at 145 and 325°C [16]. The first of these corresponds to an irreversible cis-trans isomerization. Migration of hydrogen occurs at 325°C, open chain and cross-linking without the formation of polyacetylene volatile products. The color of the polymer becomes brown. A large number of defects appears. In the infrared spectrum there are absorption bands characteristic of the CH, CH3, -C=C- and -C2H5- groups [16]. 

Ito, T., H. Shirakawa, and S. Ikeda. 1975. Thermal cis-trans isomerization and decomposition of polyacetylene. J Polym Sci Polym Chem 13 1943. 

PolyaCGtyiGnes. Polyacetylene, one of the most studied of the EAPs, possesses the simplest EAP structure, consisting of alternating single and double carbon-carbon bonds, in either a cisoid or transoid configuration. (Fig. 1). The transoid configuration is thermodynamically favored, but cis-trans isomerization is a reversible process. 

Tabata, M. Tanaka, Y Sadahiro, Y Sone, T. Yokota, K. Miura, 1. Pressure-induced cis to trans isomerization of aromatic polyacetylenes. 2. Poly((e-ethoxyphenyl)acetylene) stereoregularly polymerized using a Rh complex catalyst. Macromolecules 1997, 30, 5200-5204. 

Figure 6.39 Isomerization of cis (A) and trans (B) sequences in polyacetylene that meet to form a soliton. Reprinted, by permission, from J. M. G. Cowie, Polymers Chemistry Physics of Modem Materials, 2nd ed., p. 417. Copyright 1991 by J. M. G. Cowie.

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