Polyacetylene segments

Figure 5.7. Synthesis of block copolymers via termination reactions. Control over the molecular weight of the polyacetylene segment is afforded by varying the ratio of monomer to terminating groups (S).

Fig. 1.8 FT-IR spectrum of a PANPAC, containing 32 mol% acetylene the polyacetylene segments contain ca. 95% trans configuration (bottom) PAN (top).

Armes et al. [116] reported the synthesis of soluble polyisoprene-polyacetylene diblock copolymers with a cobalt catalyst system. The polyacetylene segment was suggested to have a molecular weight equal to 1200. A low-temperature polymerization resulted only in cw-polyacetylene blocks in the copolymer, although appreciable isomerization to a transisomer was observed over 23 h at room temperature. The electrical properties of this material have not yet been determined. 

Zhao, Y, Higashihara, T., Sugiyama, K., and Hirao, A. (2005) Synthesis of functionalized asymmetric star polymers containing conductive polyacetylene segments by living anionic polymerization. Journal the American Chemical Society, 127,14158-14159. 

Hirao, A., Karasawa, Y., Higashihara, T. et al. (2004) Synthesis of block co-polymers and star-branched polymers consisting of conducting polyacetylene segments via ionic interaction to form ionic bonds. Designed Monomers and Polymers, 1,647-660. 

Once the pair of sites is disconnected from the growing tubule [Fig. 17(d)], an orthogonal unit is inserted below the five membered ring [4° in Fig. 17(e)]. The latter inserted unit and the remaining two ci.s-polyacetylene C2 segments are finally displaced by the arrival two orthogonal C-, units [.r in Fig. 18(f)]. 

The process results in a cis-transoid structure. The formation of trans-polyacetylene is suggested to take place through isomerization of the new segment formed by cis insertion before it can crystallize.412... 

Fig. 4.2 A short segment of t rans -polyacetylene is shown with an abrupt (idealized) reversal of the bond alternation pattern (see text). Top- a neutral soliton with an unpaired spin and an energy state near the middle of the electron energy gap. Middle the addition of an electron results in the formation of a spinless negatively charged soliton. Bottom the extraction of an electron from the top results in the formation of a spinless positive soliton. The optical transitions associated with the charged solitons are indicated as arrows on the right.

The cis-trans content of polyacetylene formed with coordination catalysts depends on the polymerisation temperature the increasing trans content with increasing polymerisation temperature has been explained in terms of a thermally induced cis-trans isomerisation which occurs before crystallisation of the chain segment [10,76 78],... 

Two ended living polynorbornene 23 was prepared with difunctional initiator 22a, b, and anti-7,8-benzotricyclo[4.2.2.02,5]deca-3,7,9-triene 26 was added as a second monomer to produce a triblock copolymer with a poly(norbornene) middle segment, Eq. (29) [42b]. Naphthalene cleavage occured upon heating to temperatures above 120 °C. The product of thermolysis is polyacetylene/polynorbor-nene/-polyacetylene triblock copolymer 28. 

Copolymers with longer polyene segments were found to be insoluble in the reaction solvent (toluene). In these materials, the polyacetylene fraction was crystalline (97). Copolymers with a low acetylene content were composed of a variety of isolated crystalline structures within an amorphous matrix, whereas those containing 50% or more polyacetylene had a morphology that resembled fibrillar polyacetylene. Dried copolymer solutions and suspensions gave blue films with the mechanical properties characteristic of the carrier polymer. No increase in environmental stability was observed. 

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