The polymerization of three diarylacetylenes, namely 1-(p-benzylphenyl)-2-phenylacetylene (p-BzDPA), 1-(p-phenylphenyl)-2-phenylacetylene and 1-(beta-naphthyl)-2-phenylacetylene, was examined. These monomers polymerized in good yields with TaCl5-cocatalyst systems. Poly(p-BzDPA) was soluble in various organic solvents and had high molecular weights of 6 x 10(5)-9 x 10(5) according to gel permeation chromatography. In contrast, the other two polymers were insoluble in all solvents. All these polymers had fairly good thermal stability in air (their onset temperatures of weight loss in air were 330-450-degrees-C). The oxygen permeability coefficient of poly(p-BzDPA) at 25-degrees-C was 18 barrers, which was close to that of natural rubber (23 barrers).