Polymerization and polymer properties of 1-phenyl-2-[4-(triphenylsilyl)phenyl] acetylene (pPh(3)SiDPA) and 1-phenyl-2-[4-(triisopropylsilyl)phenyl] acetylene (piPr(3)SiDPA), which have very bulky silyl groups, were examined. These monomers polymerized in good yields in the presence of TaCl5-based catalysts. The highest weight-average molecular weights of poly(pPh(3)SiDPA) and poly(piPr(3)SiDPA) reached about 1 x 10(6) and 4.8 x 106, respectively. The polymers were yellow to orange-colored solids which were soluble in toluene, chloroform, etc., and provided free-standing films by solution casting. The onset temperatures of weight loss of poly(pPh(3)SiDPA) and poly(piPr(3)SiDPA) in TGA in air were 430 and 270 degrees C, respectively. The oxygen permeability coefficients of poly(pPh(3)SiDPA) and poly(piPr(3)SiDPA) at 25 degrees C were 3.8 and 20 barrers, respectively, and relatively small.