Homopolymerization of p-[tris(trimethylsilyl)silyl]phenylacetylene [p(Me3Si)(3)SiPA] by Rh catalyst provided insoluble polymer. On the other hand, copolymerization of p(Me3Si)(3)SiPA with p-(trimethylsilyl)phenylacetylene (pMe(3)SiPA) at 80:20, 50:50, and 20:80 feed ratios afforded high molecular weight copolymers (M-w > 1 x 10(6)), all of which were soluble in common solvents such as toluene and chloroform. The mole ratios of p(Me3Si)(3)SiPA to pMe(3)SiPA unit in copolymers were close to those in the feeds. The oxygen permeability increased monotonously with increasing p(Me3Si)(3)SiPA content of copolymer in correspondence with fractional free volume; the value of the copolymer for the 80:20 feed ratio reached 770 barrers.