Polymerization of several diphenylacetylene derivatives was carried out by using TaCl5-n-Bu4Sn as catalyst. C6H5C=-CC6H4-p-OSi(CH3)(2)t-Bu (3a) and C6H5C&3bond; CC6H4-M-OSi(CH3)(2)t-Bu (3b) provided the corresponding polymers (poly(3a), poly(3b)) with high molecular weights in good yields, while p-t-Bu(CH3)(2)SiOC6H4C&3bond; CC6H4-p-OSi(CH3)(2)t-Bu (3c), p-t-Bu(CH3)(2)SiOC6H4C&3bond; CC6H4-m-OSi(CH3)(2)t-Bu (3d), and m-t-Bu(CH3)(2)SiOC6H4C&3bond; CC6H4-m-OSi(CH3)(2)t-Bu (3e) did not satisfactorily. Desilylation of poly(3a) and poly(3b) membranes catalyzed by trifluoroacetic acid yielded poly(diphenylacetylenes) having free hydroxyl groups [poly(4a), poly(4b)], which are the first examples of highly polar group-carrying poly(diphenylacetylenes). Poly(3a) and poly(3b) dissolved in nonpolar solvents such as toluene and chloroform, while poly(4a) and poly(4b) were insoluble in these solvents. According to TGA in air, poly(3a) and poly(3b) were thermally fairly stable among substituted polyacetylenes, and poly(4a) and poly(4b) displayed even higher thermal stability. The P-CO2/P-CH4 and P-CO2/P-N2 permselectivity ratios of poly(4a) and poly(4b) membranes were as large as 13-46, while keeping relatively high P-CO2 values.