Preparation of polyacetylene

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... 

Scheme 2. Preparation of polyacetylene 2 (n 32) using the coupling procedure described by Hay. (ODCB o-dichloroben-zene, TMEDA N,N,N, N -tetramethylethylenediamine.)...

An alternative approach to the preparation of polyacetylene is provided by the ring-opening polymerisation of 1,3,5,7-cyclooctatetraene in the presence of a metathesis catalyst, e.g. WCU—AlEt2Cl-epichlorohydrin (Cl4W[OCH(CH2Cl)2 —AlEt2Cl) [157-163] ... 

The recent interest in electroactive polymers started with the preparation of polyacetylene (CH) film [4] and the discovery of the exceptional electrical... 

When acetylenic halogen compounds are treated with base, dehydrohalogenation occurs followed by rearrangement to yield the more stable conjugated acetylenic compounds exclusively [ 123,124]. This reaction is used for the preparation of polyacetylenic compounds. 

The Durham route allows the preparation of polyacetylene in the form of continuous uniform and featureless films, as opposed to the entangled fibrillar morphology obtained by the direct polymerization of acetylene. 

The intractability of the early preparations of polyacetylene has severely hampered the establishment of clear-cut relationships between structure, morphology and (electrical) properties. An early example of an integrated approach to structure-property relations is a paper by Haberkom et al. [24], From a combination of x-ray data with NMR and IR investigations, these authors have found a relationship between the content of sp defects and crystallinity in polyacetylene prepared by the Shirakawa, Luttinger and other methods. Such defects are apparently expelled to the amorphous phase. The authors find a correlation with conductivity in both undoped and iodine-doped samples. 

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 ... 

For the ECPs with degenerated ground state, solitons are responsible for the charge transport. Such a polymeric system is polyacetylene. The major problem on the preparation of polyacetylene/Cgjj nanocomposite is the insolubility of polyacetylene. This has led to the discovery of soluble polyacetylene derivatives such as poly(o-trimethylsilylphenylacetylene) (PTMSiPA) [28]. Small amoimts of doping in PTMSiPA is found to enhance the photoconductivity of pristine PTMSiPA [29]. 

ROMP reactions are unique in that all the unsaturation present in the monomers is conserved in the polymeric product. This feature makes ROMP techniques especially attractive for the preparation of highly unsaturated, fully conjugated materials. One example is the direct preparation of polyacetylene by the ROMP technique through one of the double bonds of cyclooctatetraene. For further discussion of polyacetylene, see "Chemical Connections Organic Polymers That Conduct Electricity" earlier in this chapter. 

Two approaches currently seem open. The first is directed toward conjugated polymers. Here substituted systems may hold potential. Cyclopol3nnerization is a viable method of synthesis of substituted polyacetylenes. Likewise, chemical modification of polyacetylene itself may have potential. The preparation of polyacetylenes by elimination reactions from precursor polymers needs more attention. The second approach is toward non-conju-gated polymers containing aromatic functionalities little work has been done in this area. Much creative chemistry remains to be explored and it will most likely involve new monomers and polymers. ... 

Krouse, S.A. andSchrock, R.R. (1988) Preparation of polyacetylene chains in low-polydispersity diblock and triblock copolymers. Macromolecules, 21,1885-1888. 

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