Polyacetylene block copolymers

Aldissi, M., Soluble conducting polyacetylene block copolymers, J. Chem. Soc. Chem. Commun., 32, 1347-1351 (1984). 

Scherman, O.A., Rutenberg, I.M., and Grabbs, R.H. (2003) Direct synthesis of soluble, end-functionabzed polyenes and polyacetylene block copolymers. Journal of the American Chemical Society, 125,8515—8522. 

Copolymerizations of benzvalene with norhornene have been used to prepare block copolymers that are more stable and more soluble than the polybenzvalene (32). Upon conversion to (CH), some phase separation of nonconverted polynorhornene occurs. Other copolymerizations of acetylene with a variety of monomers and carrier polymers have been employed in the preparation of soluble polyacetylenes. Direct copolymeriza tion of acetylene with other monomers (33—39), and various techniques for grafting polyacetylene side chains onto solubilized carrier polymers (40—43), have been studied. In most cases, the resulting copolymers exhibit poorer electrical properties as solubiUty increases. 

Another approach to blending of polyacetylene with tough polymers is to form graft or block copolymers 280,281). Aldissi282) produced block copolymers by polymerizing acetylene at the ends of chains of anionic polyisoprene after conversion of... 

Aldissi 586) has reviewed the stability of block copolymers of acetylene and other non-conducting blocks. The copolymers are somewhat more stable than polyacetylene but the effect is small. 

In contrast, organophilic PV membranes are used for removal of (volatile) organic compounds from aqueous solutions. They are typically made of rubbery polymers (elastomers). Cross-linked silicone rubber (PDMS) is the state-of-the-art for the selective barrier [1, 43, 44]. Nevertheless, glassy polymers (e.g., substituted polyacetylene or poly(l-(trimethylsilyl)-l-propyne, PTMSP) were also observed to be preferentially permeable for organics from water. Polyether-polyamide block-copolymers, combining permeable hydrophilic and stabilizing hydrophobic domains within one material, are also successfully used as a selective barrier. 

Polyacetylene latexes (48) have been prepared by polymerizing acetylene in the presence of poly[(fert-butylstyrene)-fo-(ethylene oxide)]. The use of a tetrahydrofuran/cyclohexane (THF/cyclohexane) solvent combination led to the formation of a stable dispersion of nearly uniform spherical polyacetylene particles 40-200 nm in diameter. The block copolymer was separated from the polyacetylene by several wash cycles with a good solvent for the block copolymer (cyclohexane), and after removing the solvent, a polyacetylene powder was obtained. On the basis of nitrogen adsorption... 

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).

The third route involves metathesis polymerization of cyclooctatetraene with tungsten catalysts, yielding polyacetylene as an insoluble film along with oligomers (iOi). By first polymerizing cyclooctene and then adding cyclooctatetraene, a soluble, red block copolymer was obtained. On the basis of the visible absorption spectrum, at least two or three cyclooctatetraene units were concluded to have been added to the polymer chain forming a short polyacetylene block. No conductivity data were reported for this copolymer. 

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. 

Graupner, W., Leising, G., Fischer, W., and Stelzer, F., Photoinduced absorption in polyacetylene polynorbomene block copolymers, Synth. Met., 58, 77-94 (1993). 

In these two decades remarkable progress has been made in the development of excellent catalysts for living and stereospecific acetylene polymerizations (10,26-28). The r-conjugated polymers prepared by the sequential polsrmerization are strictly limited to polyacetylenes, except for only a few examples. Thus, synthesis of tailor-made conjugated macromolecules such as end-functionalized polymers, block copolymers, star-shaped polymers is possible only in the case of substituted acetylenes. 

Choi et al. [46], EVE ethyl vinyl ether, and (c) cross-linking of the polyacetylene blocks of block copolymer 73 by dimerization of the generated ketene moieties. 

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