Effects of organometallic cocatalysts on the polymerization of disubstituted acetylenes by TaCl5 and NbCl5

The effects of organometallic cocatalysts on the polymerization of disubstituted acetylenes were investigated. Diphenylacetylene did not polymerize with TaCl₅ alone, while it produced a polymer quantitatively in the presence of appropriate cocatalysts (Me₄Sn, Et₃SiH, etc.). The poly(diphenylacetylene) formed was an insoluble yellow solid. 1-Phenyl-1-alkynes (1-Phenyl-1-butyne and -1-octyne) polymerized with TaCl₅ and NbCl₅ alone to yield polymers whose weight-average molecular weights (M _w's) were ca. 5 × 10⁵. Use of cocatalysts (nBu₄Sn etc.) to the polymerization of these monomers accelerated the reaction, and increased the polymer molecular weights up to ca. 1.5 × 10⁶. The poly(1-phenyl-1-alkynes) were soluble white solids. Internal octynes (2-, 3-, and 4-octynes) gave mixtures of a polymer and cyclotrimers with TaCl₅ alone. In contrast, cyclotrimers formed virtually selectively by addition of cocatalysts. Thus, various effects of organometallic cocatalysts were observed depending on the kind of monomer.