Conjugated polyacetylenes

Extending the metathesis polymerization methodology to other cyclooctate-traene derivatives, provides a convenient route to a variety of substituted polyacetylene derivatives. For example, soluble conjugated polyacetylene derivatives can be prepared through the ROMP of trimethylsilylcyclooctatetraene (40) Eq. (41) [60 a d]. 

Table 7. Triple-bond stretching frequencies for conjugated polyacetylenes, R(C=C) R ...

Chodkiewicz, W., Cadiot, P. New synthesis of symmetrical and asymmetrical conjugated polyacetylenes. Compt. rend. 1955, 241, 1055-1057. 

In a related vein, it is of interest to apply the LSA to a case where the local interaction occurs within the delocalized system rather than at a surface. One example is an impurity embedded in a 3-dimensional metal. Another example, that we have examined [40], is the cleavage of a (formal) C-C single bond in a 7r-conjugated polyacetylene chain. Using an INDO Hamiltonian it was found that a local space containing only one or, at most, two carbon n AOs on either side of the broken bond is sufficient to completely restore the 7r-conjugation. 

Musikabhumma, K. Masuda. T. Synthesis and properties of widely conjugated polyacetylenes having anthryl and phenanthryl pendant groups. J. Polym. Sci., Part A Polym. Chem. 1998, 36, 3131-3137. 

Ginsburg EJ, Gorman ChB, Marder SR, Gmbbs RH (1989) Poly (trimethylsilylcyclo-octatetraene) a soluble conjugated polyacetylene via olefin metathesis. J Am Chem Soc 11 7621-7622... 

One particularly successful method utilizes a soluble precursor system with polymerization being completed via the elimination of a small molecule to leave the fully conjugated polyacetylene chain. The route employs a fluorinated cyclic precursor molecule that is soluble in acetone and castable into continuous clear films (Fig. 1.5). 

Polyacetylenes. The first report of the synthesis of a strong, flexible, free-standing film of the simplest conjugated polymer, polyacetylene [26571-64-2] (CH), was made in 1974 (16). The process, known as the Shirakawa technique, involves polymerization of acetylene on a thin-film coating of a heterogeneous Ziegler-Natta initiator system in a glass reactor, as shown in equation 1. 

Polyacetylene is considered to be the prototypical low band-gap polymer, but its potential uses in device applications have been hampered by its sensitivity to both oxygen and moisture in its pristine and doped states. Poly(thienylene vinylene) 2 has been extensively studied because it shares many of the useful attributes of polyacetylene but shows considerably improved environmental stability. The low band gap of PTV and its derivatives lends itself to potential applications in both its pristine and highly conductive doped state. Furthermore, the vinylene spacers between thiophene units allow substitution on the thiophene ring without disrupting the conjugation along the polymer backbone. 

The excellent agreement between the TSC and P1A results has two implications. First, since the TSC method probes the product of mobility and carrier density, while the P1A probes only the carrier density, there seems to be no dominant influence of temperature on the carrier mobility. This was also found in other conjugated polymers like /ra/ry-polyacetylene [19, 36]. Second, photoconductivity (observed via the thermal release of photoexcited and trapped earners) and photo-induced absorption probe the same charged entity [36, 37J. 

Oxidative polymerization of trans-bis-deprotected 79 under Hay coupling conditions [54] yielded, after end-capping with phenylacetylene, the high-melting and readily soluble oligomers 80a-e with the poly (triacetylene) backbone [87,106] (Scheme 8). Poly(triacetylene)s [PTAs,-(C=C-CR=CR-C=C) -] are the third class of linearly conjugated polymers with a non-aromatic allcarbon backbone in the progression which starts with polyacetylene [PA,... 

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