Poly(1-trimethylsilyl-1-propyne) (PTMSP) has been crosslinked using 4,4'-diazidobenzophenone bisazide to improve its chemical and physical stability over time. Crosslinking PTMSP renders it insoluble in good solvents for the uncrosslinked polymer. Gas permeability and fractional free volume decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PTMSP was due to decrease in diffusion coefficient. Compared with the pure PTMSP membrane, the permeability of the crosslinked membrane is initially reduced for all gases tested due to the crosslinking. By adding nanoparticles (fumed silica, titanium dioxide), the permeability is again increased; permeability reductions due to crosslinking could be offset by adding nanoparticles to the membranes. Increased selectivity is documented for the gas pairs O-2/N-2, H-2/N-2, CO2/N-2, CO2/CH4. and H-2/CH4 using crosslinking and addition of nanoparticles. Crosslinking is successful in maintaining the permeability and selectivity of PTMSP membranes and PTMSP/filler nanocomposites over time. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3078-3088, 2009