Copolymers of 1-trimethylsilyl-1-propyne (TMSP) with 1-(3,3,3-trifluoropropyldimethylsilyl)1-propyne (TFPS) as part of a systematic series with the TFPS content of the final polymer in the range of 0 to 46 mol % have been synthesized. The resulting samples have been characterized by different instrumental methods including NMR, IR, and DSC techniques. It has been shown that the accessible free volume of the polymer decreases from 30.4 to 19.1% with an increase in the proportion of TFPS units. Moreover, the gas transport properties of the membrane materials are reduced by factors of 30 (oxygen), 50 (nitrogen), and 15 (carbon dioxide), although the selectivity for the O-2/N-2 and CO2/N-2 gas pairs increases from 1.6 to 2.5 and 2.5 to 11.5, respectively. A study of nanofiltration of organic media has shown that the ethanol permeability through the TFPS-co-TMSP copolymer material is reduced by no more than 30%, a value that is comparable with the relative decrease in the fractional free volume of the polymer. An increase in the TFPS content has improved the stability of the membrane material in ethanol (swelling ratio decreased from 61 to 39%), thereby resulting in an increase in the retention of the Orange II anionic dye (350 g/mol) from 89 to 94%.