The polymerization of 1,2-disubstituted acetylenes [1-(trimethylgermyl)-1propyne and 1-(trimethylsilyl)-1-propyne] initiated by Nb-and Ta-based catalytic systems was studied within a wide temperature range (Ϫ10 to ϩ80°C) with solvents (cyclohexane, CCl 4 , toluene, anisol, and n-chlorobutane) with variable dielectric constants (2.023-7.390). Conditions ensuring the synthesis of poly[1-(trimethylsilyl)-1propyne] (PTMSP) containing 20 -80% cis units and poly[1-(trimethylgermyl)-1-propyne] (PTMGP) containing 3-65% cis units were determined. The PTMSP and PTMGP samples were amorphous, exhibited a two-phase structure characterized by the presence of less ordered regions and regions with an enhanced level of ordering, and differed in solubility. A correlation was found between the cis/trans ratio and the morphology, the geometrical density of PTMSP and PTMGP films, and the gas permeability of the polymers. The gas permeability and solubility behavior of PTMSP and PTMGP were examined in terms of the molecular characteristics of the polymer samples (the thermodynamic Kuhn segment and the Kerr electrooptic effect). It was demonstrated that the gas permeability, as well as the solubility of the polymers, was defined by their supramolecular ordering, which depended on the lengths of continuous sequences composed of units of analogous microstructures and on the flexibility of macrochains.