Polyacetylene from cyclooctatetraenes

Gorman, C.B., Ginsburg, E.J., Grubbs, R.H., 1993. Soluble, highly conjugated derivatives of polyacetylene from the ring-opening metathesis polymerization of monosubstituted cyclooctatetraenes synthesis and the relationship between polymer structure and physical properties. I. Am. Chem. Soc. 115, 1397-1409. 

Figure 8 The Durham route (top) and a direct route from cyclooctatetraene accessing polyacetylene. Reproduced with permission from Edwards, J. H. Feast, W. J. J. Polym. 1980, 21, 595 Korshak, Y. V. Kanischka, G. Mocker, H. Makromol. Chem. Rapid Commun. 1985, 6, 685. ...

Optically active polyacetylene derivatives 97 were synthesized through ring-opening polymerization of the corresponding cyclooctatetraene derivatives.25 A twisted conformation of the main chain was proposed on the basis of CD and UV absorptions. Various optically active polyacetylenes have also been prepared from chiral monomers.24,25,263,177-183 The examples include a phenylacetylene derivative (98),26a alkylacetylenes 99,24 propionic esters such as 100,177,178 a Si-containing monomer (101),179 and disubstituted monomers such as 102.180 Poly-(A)-98 synthesized using a [RhCl(norbornadiene)]2 catalyst shows intense CD bands in the UV—vis region, probably based on a predominant helical sense of the main chain.263 This polymer effectively resolves several racemic... 

Additional improvements in preparations of polyacetylene came from several developments. One is the use of metathesis polymerization of cyclooctatetraene, catalyzed by a titanium alkylidene complex. The product has improved conductivity, though it is still intractable and unstable. By attaching substituents it is possible to form soluble and more stable materials that can be deposited from solution on various substrates. Substitution, however, lowers the conductivity. This is attributed to steric factors introduced by the substituents that force the double bonds in the polymeric chains to twist out of coplanarity." Recently, a new family of substituted polyacetylenes was described. These polymers form from ethynylpyridines as well as from ethynyldipyridines. The polymerization reaction takes place spontaneously by a quatemization process ... 

Possibly the most convenient direct route to polyacetylene, namely the polymerisation of cyclooctatetraene (COT), was introduced by Grubbs and co-workers [4], They initially showed that polyacetylene can be obtained via ROMP of COT using the very active Schrock type tungsten hexafluoro-t-butoxide initiator W(=CHR)(OC(Cp3)2 CH3 )2(=NAr). A freestanding film was obtained when the monomer was polymerised as the neat liquid. A random copolymer was obtained from the polymerisation of a mixture of COT and 1,5-cyclooctadiene (COD) and, as expected, a gradation in colour and Raman shift showed that the conjugation length of the polyene sequences increased with COT... 

Jozefiak, T. H., Ginsburg, E. J., Gorman, C. B., Grubbs, R. H., and Lewis, N. S., Voltammetric characterization of soluble polyacetylene derivatives obtained from the ring opening metathesis polymerization (romp) of substituted cyclooctatetraenes, J. Am. Chem. Soc., 115, 4705-4713 (1993). 

Ambiphilic block copolymers incorporating polyacetylene have also been synthesized via ROMP (Figure 10). The Durham route was followed to form the polyacetylene while a silyl ester protected dicarboxylic acid norbornene monomer was used to form the hydrophilic block. Employment of the Langmuir-Blodgett technique, which forms ordered molecular layers based on the hydrophilic-hydophobic interactions between the polymer and the surface, enabled the fabrication of films that exhibited superior conductivity over spin-coated or bulk cast films of the same composition. Even electroche-mically activated catalysts have been successfully used in the ROMP of cyclooctatetraene, but in general the research into polyacetylene has diminished in recent decades relying more on other polyenes (e.g., polythiophene and polyphenylene) that exhibit the conductivity desired from polyacetylene as well as better solubilities and stabilities. 

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