Crystal structures poly acetylene

The liquid crystal polymerization method was modified to prepare a vertically aligned poly acetylene film [58]. As a result, a film with a very curious morphology was formed that was composed of two layers. The layer on the solvent side had a vertically oriented fibrillar structure, whereas the layer on the acetylene gas side had a randomly oriented one. The modified method is very promising for visualizing the polymer growth process and clearly demonstrates that PA chains grow in a liquid crystal solvent. 

If polyacetylene is oxidized by either of the methods described in the proceeding section, the reaction product has a crystal structure different from the pristine polymer. This was first observed for the oxidation by treatment with iodine, AsFc-etc. by R. H. Baughman et al. The diffraction patterns of electrochemically oxidized poly(acetylene) containing AsFg, CIO, and SbF as the counterions were investigated by Monkenbusch et al. Further work on the diffraction pattern of iodinated polyacetylene is available from a number of other sources, especially from Shimamura et al. on the diffraction from oriented samples. 

Pristine poly(acetylene) in either cis- or trans-form exhibits optical spectra typical for a semiconductor. The absorption peak of the cis-polymer is structured with maxima at 2.1, 2.3 and 2.4 eV, the absorption coefficient is about 4 10 cm" The structureless and very broad absorption of the trans-polymer peaks at 1.9 eV with an absorption coefficient of 3 10 cm . The large halfwidth of the peak is generally explained as being due to the rather broad chain length distribution in addition, the small crystallite size and crystal defects may contribute to the broadening. A discussion is still ungoing whether the peak is linked to a direct interband transition or whether it is of an excitonic character.2-4, 7,32... 

A Ta vinylalkylidene complex 6, confirmed by a single crystal X-ray analysis, was revealed to polymerize 2-butyne in a manner of living polymerization.The initiation efficiency is quantitative, and the living end can be end-capped with aromatic aldehydes. As polymers from symmetric acetylenes are generally insoluble, soluble poly(2-butyne) is accessible if the degree of polymerization is suppressed below 200. The NMR analysis of living oligomers of 2-butyne clearly indicates that both cis- and 7ra r-structures exist in the main chain. 

Fully conjugated and fully chain-aligned polymer single crystals with planar polymer backbone are obtained, which may have the alternative acetylene (ynene) or butatriene structures of Eq. (1). From our experiment we know that the acetylene structure is dominant in the polymer molecules. Up to now the best investigated diacetylene crystals are the TS-6 monomer crystals and the corresponding polymer crystals (poly TS-6). The substituents R and the notation of further diacetylene crystals discussed below are listed in Table 1. 

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