High-molecular-weight poly[1-phenyl-2-(4-t-butylphenyl)acetylenel], poly-[1-phenyl-2-(4-trimethylsilylphenyl) acetylene], and their copolymers were synthesized by the polymerization with TaCl5-n-Bu4Sn. The obtained polymers were sulfonated by using acetyl sulfate to give sulfonated poly(diphenylacetylene)s with different degrees of substitution. The degrees of sulfonation of poly[1-phenyl-2-(4-t-butylphenyl)acetylene] and copolymers were in the range of 0.57-0.85. When poly[1-phenyl-2-(4-ti methylsilylphenyl)acetylene] was sulfonated, the sulfonated poly(diphenylacetylene) with the highest degree of sulfonation was obtained among all the polymers in this study. Its degree of sulfonation was 1.55. All the sulfonated polymers exhibited high CO2 permselectivity, and their CO2/N-2 separation factor were over 31. The sulfonated poly(diphenyl acetylene) with the highest degree of sulfonation showed the highest CO2/N-2 separation factor of 75. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6463-6471, 2009