Polyacetylenes, crystallinity substituted

The ROMP of 136 may be used as the first stage in the preparation of polyacetylene molecules with mesogenic (liquid-crystalline) functional groups at the chain ends the ROMP of 136 is initiated by a molybdenum carbene complex and the living ends terminated by reaction with a substituted benzaldehyde bearing a mesogenic group, followed... 

Table 26 shows X-ray diffraction data of polyacetylenes and those of polyethylenes for comparison. The ratios of half-height width to diffraction angle (A28/28) for the substituted polyacetylenes are all larger than 0.20. The value for amorphous polyethylene is similar to these values, while those of crystalline polyethylene and cis-polyacetylene89) are much smaller. Therefore, it is concluded that the present polymers are amorphous. This must be due to the presence of bulky substituents and/or the non-selective geometric structure of the main chain. 

Substitution on polyacetylene reduces the crystallinity of the polymer and also decreases its conductivity. Solubility increases with substitution. 

Also shown in Table lO-l is an (alkylcyclohexylaryloxy)-substituted polyacetylene [77]. Polymers of this general structure have been found to display liquid-crystalline behavior. In contrast to vinyl-based liquid-crystalline polymers, the geometric isomerism of the main-chain double bonds plays a role in determining the type of phase that is found. Advincula et al. have examined Langmuir films of polyacetylenes at the air-water interface [78]. Polyacetylene derivatives are unusual in that the polymer backbone itself acts as a chromophore therefore, in studies such as these, UV-visible spectroscopy can be a sensitive probe of polymer conformation. 

V. Non-catalytic high-pressure polymerization. A solid-state polymerization of substituted diacetylene has been known for many years and is described in Section IV. Acetylene also undergoes polymerization in the molecular-crystalline orthorhombic phase at room temperature and pressures above 3.5 GPa The polymerization was carried out in a diamond anvil that has 0.7-mm-diameter faces. Dominant formation of rmn.s-polyacetylene confirmed by Raman spectroscopy suggested that acetylene undergoes trans opening of the triple bond and is polymerized along the diagonal of the be plane of the unit cell. 

B.A. San Jose, S. Matsushita, K. Akagi, Lyotropic chiral nematic liquid crystalline aliphatic conjugated polymers based on di-substituted polyacetylene derivatives that exhibit high dissymmetry factors in circularly polarized luminescence. J. Am. Chem. Soc. 134, 19795-19807 (2012)... 

K. Akagi, H. Goto, K. lino, H. Shirakawa, J. Isoya, Electrically conducting liquid crystalline polymers, mono-substituted polyacetylene derivatives. Mol. Cryst. Liq. Cryst., 267, 277-282 (1995). 

FIGURE Iti Schematic representation of magnetically forced alignment of the side chain liquid crystalline mono-substituted polyacetylene and sample cell for the four-probe method of electrical conductivity measurement. 

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