Diarylacetylenes having fluorenyl groups and other substituents (trimethylsilyl, t-butyl, bromine, fluorine) (1a-1) were polymerized with TaCl5-n-Bu4Sn. Monomers 1a-1 produced high molecular weight polymers 2a-1 (M-w 5.1 x 10(5)-1.3 x 10(6)) in 12-59% yields. All of the polymers were soluble in common organic solvents, and gave tough free-standing membranes by the solution casting method. The onset temperatures of weight loss of polymers 2a-1 in air were over 400 degrees C, indicating considerably high thermal stability. All the polymer membranes showed high gas permeability; e.g., the oxygen permeability coefficient (PO2) of 2a was as large as 4800 barters. Membrane 2d possessing two fluorine atoms at meta and para positions of the phenyl ring showed the highest oxygen permeability (PO2 = 6600 barters) among the present polymers. (C) 2009 Elsevier Ltd. All rights reserved.