Magnesium oxide (MgO) nanoparticles were dispersed via solution processing in trimethylsilyl-substituted polyacetylenes to form polymer nanocomposites. In the presence of these particles, the polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA), were partially desilylated. Some PTMSDPA/MgO nanocomposites were insoluble in common solvents (e.g., toluene or chloroform), and the solubility characteristics depended on particle loading and preparation conditions. When possible, the reaction products were characterized using XPS, FTIR, and NMR. Small molecule model compounds were also used to study the reaction of trimethylsilyl groups with MgO nanoparticles. The CO2 permeability in these nanoparticle-filled films was over 6 times higher than in the analogous unfilled polymers. This phenomenon may provide a route for preparing highly permeable, chemically stable membranes for gas separations.