Polymerization of Monosubstituted Acetylenes

Typical examples of the polymerization of monosubstituted acetylenes are shown in Table 3. Transition metal catalysts that involve Mo, W, and Rh are particularly effective. Whereas Mo and W catalysts are sensitive to polar groups in the monomer, Rh catalysts are tolerant to such groups. Another point is that Mo and W catalysts are effective to various sterically crowded monomers, while Rh catalysts are useful to rather restricted kinds of monomers including... 

Rh complexes are examples of the most effective catalysts for the polymerization of monosubstituted acetylenes, whose mechanism is proposed as insertion type. Since Rh catalysts and their active species for polymerization have tolerance toward polar functional groups, they can widely be applied to the polymerization of both non-polar and polar monomers such as phenylacetylenes, propiolic acid esters, A-propargyl amides, and other acetylenic compounds involving amino, hydroxy, azo, radical groups (see Table 3). It should be noted that, in the case of phenylacetylene as monomer, Rh catalysts generally achieve quantitative yield of the polymer and almost perfect stereoregularity of the polymer main chain (m-transoidal). Some of Rh catalysts can achieve living polymerization of certain acetylenic monomers. The only one defect of Rh catalysts is that they are usually inapplicable to the polymerization of disubstituted acetylenes. Only one exception has been reported which is described below. 

Typical examples of the polymerization of monosubstituted acetylenes are shown in Table 5. As seen, Fe, Mo, W and Rh catalysts, all of which involve transition metals, are particularly effective. It is noted that not only sterically unhindered monomers but also very crowded ones afford high molecular weight polymers. 

Oh, S. Y., Ezaki, R., Akagi, K., and Shirakawa, H., Polymerization of monosubstituted acetylenes with a liquid crystalline moiety by Ziegler Natta and metathesis catalysts, J. Polym. ScL A Polym. Chem., 31, 2977-2985 (1993). 

Monosubstituted acetylenes generally prefer cyclotrimerization to polymerization in the presence of halides of Group 5 metals as described earlier (135-137). Tbe polymerization of monosubstituted acetylenes by NbCls and TaCls catalysts is possible only in the case of sterically crowded monomers, which is exemplified by the polymerization of 3-trialkylsilyl-l-alkynes with the formula of HC CH(Si(CH3)2R)R (R = CHg, n-CeUis, CgHs R = ra-CgHT, n-C5H11, ra-CyHis) (45). Even tert-butylacetylene affords a low yield of polymer in the presence of TaCls or NbCls. Additionally, the molecular weights of these Ta- and Nb-based poly(tert-butylacetylene)s are lower than those of the W-based ones. However, there has been a demonstration of the imique ability of... 

The Rh-catalyzed polymerization of monosubstituted acetylenes proceeds in various solvents including benzene, tetrahydrofiiran (THF), ethanol, and triethylamine (Et3N). Among these solvents, ethanol and EtsN are most favorable for phenylacetylenes from the viewpoint of both... 

Figure 8 Ruthenium carbene catalysts for the polymerization of monosubstituted acetylenic monomers.

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