The polymerization of various silyl- and F-containing diphenylacetylenes (1a-k) with TaCl5- n-BU4Sn provided high-molecular-weight polymers. Most polymers (2a-d, 2g, and 2h) were totally soluble in common organic solvents and afforded tough free-standing membranes by casting from toluene solution, while some polymers (2e, 2f, and 2i-k) were insoluble in any organic solvents. The onset temperatures of weight loss of polymers 2a-d in air were over 400 *C, indicating very high thermal stability. The membranes of 2a-d were desilylated with trifluoroacetic acid to give desilylated polymer membranes 3a-d, which were insoluble in any solvents. The fractional free volumes (FFV) of the present membrane-forming trimethylsilyl and/or F-bearing polymers (2a-d and 3a-d) were ca. 0.28-0.31 and appreciably large, and they showed very high permeability (ca. 1400-14 000 barrers) to the six gases examined. The oxygen permeability coefficient (P-O2) of 2a was as high as 2900 barrers, which is about twice that of poly[1-(p-trimethylsilyl)phenyl-2-phenylacetylene]. The incorporation of F atoms into both poly[1-(p-trimethylsilyl)phenyl-2-phenylacetylene] and poly(diphenylacetylene) generally enhanced gas permeability.