Polyacetylene molecular weight

Durham route, the metathesis polymerization of 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0]deca-3,7,9-triene gives a high-molecular weight soluble precursor polymer that is thermally converted to polyacetylene (equation 19.6). The precursor polymer is soluble in common organic liquids and easily purified by reprecipitation. The end product can be aligned giving a more compact material with bulk densities on the order of 1.05 —1.1 g/cm. ... 

Polyacetylene derivatives and corresponding number-average molecular weights are provided in Table 1. 

Polyacetylene may also be produced from a soluble precursor polymer by the Durham route, described earlier. In- this case the soluble precursor can be studied by conventional solution methods, provided that it is kept cold enough to prevent transformation. The molecular weight of the precursor has been determined by light scattering and low-temperature GPC 326) and corresponds to a polyacetylene chain with a molecular weight of about 200,000, with Mw/Mn of about 2. 

Castiello, D., Cimino, G., De Rosa, S., De Stefano, S., and Sondo, G., High molecular weight polyacetylenes from the nudibranch Peltodoris atromaculata and the sponge Petrosia ficiformis, Tetrahedron Lett., 21, 5047, 1980. 

It should be noted that the metal-poly-yne polymers except Pt-D -D1 are soluble in a variety of organic solvents such as benzene, toluene, tetrahydrofuran, and methylene chloride in spite of the fact that they contain a heavy metal in the backbone, whereas polymers containing conjugated unsaturation such as polyacetylene and poly(p-dieth-ynylbenzene) are practically insoluble in orgnaic solvents. Even a high molecular weight sample (Mw = 105) of Pt-D1 polymer dissolves in trichloroethylene at least up to a concentration of 50wt-%. 

A high-molecular-weight, insoluble polymer is obtained when perfluoro-2-butyne is subjected to various initiators for free-radical polymerisation (Figure 7.87). The off-white colour of this material is remarkable for a polyacetylene [307, 308]. Indeed, it is largely ignored in discussions on polyacetylenes because, of course, the fact that it is not coloured also means that the system is not conjugated the trifluoromethyl groups keep the TT-systems out of plane relative to each other. 

Various vinyl polymers 1 are manufactured on a large scale, whereas practically no polyacetylenes 2 are produced by the industries. One of the reasons is that it was difficult to synthesize high polymers from acetylenes in good yields. However, the synthesis of high-molecular-weight polyacetylenes is currently becoming feasible. 

This review describes the synthesis and properties of polyacetylenes with substituents (substituted polyacetylenes) mainly on the basis of our recent studies At first, Sections 2 and 3 survey the synthesis of substituted polyacetylenes with group 6 (Mo, W) and group 5 (Nb, Ta) transition metal catalysts respectively, putting emphasis on new, high-molecular-weight polyacetylenes. Then, Section 4 refers to the behavior and mechanism of the polymerization by these catalysts. Further, Section 5 explains the alternating double-bond structure, unique properties, and new functions of substituted polyacetylenes. Finally, Section 6 provides detailed synthetic procedures for substituted polyacetylenes. 

In Table 19 are collected typical monomers that polymerize with group 5 and 6 transition metal catalysts to produce high-molecular-weight (Mw > 1 x 10s) polyacetylenes. Among them, tert-butylacetylene and 3-(trimethylsilyl)-l-octyne are monosubstituted acetylenes, while the others are disubstituted ones. It is noteworthy that all of these monomers are considerably sterically crowded. By judicious choice of polymerization conditions, the polymer yield becomes fair to quantitative in every case. The Rtw s of the polymers reach ca. 3 x 10s 2 x 106. 

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