AbstractPoly(1-trimethylsilyl-1-propyne) modified with quaternary ammonium salts was synthesized. The introduction of salts into the polymer structure was accomplished by two-stage process: bromination of initial polymer with consequent functionalization with ternary alkylamines, namely trimethylamine and triethylamine. The presence of ammonium salts in the polymer was confirmed by element analysis and IR spectroscopy. X-ray diffraction method was used for investigation of polymer packing. TGA investigation confirmed high thermal and oxidative stability of studied materials. Gas permeability, diffusion and solubility coefficients were obtained for CO2, N2 and CH4. Due to increased solubility of CO2 in the polymer matrix containing quaternary ammonium salts the ideal selectivity of CO2/N2 and CO2/CH4 was increased in comparison to pure PTMSP.