(p-tert-Butyl-o,o-dimethylphenyl)acetylene (BDMPA) polymerized in high yields in the presence of W and Mo catalysts. Especially the W(CO)(6)-CCl4-hv catalyst quantitatively produced a polymer totally soluble in toluene and chloroform. The weight-average molecular weight of this polymer exceeded 2 x 10(6). Poly(BDMPA) was a dark brown solid, and had alternating double bonds along the main chain. The weight loss of the polymer in air occurred only above 300 degrees C, indicating a fairly high thermal stability. A free-standing film could be fabricated by solution casting. The electrical conductivity of the polymer at 25 degrees C was 1 x 10(-13) S cm(-1). The oxygen permeability coefficient and the separation factor of O-2 vs. N-2 of the polymer at 25 degrees C were 67 barrers and 3.2, respectively.