Crosslinking poly[1-(trimethylsilyi)-1-propynel (PTMSP) films with 3,3'-diazidodiphenylsulfone, a bis(azide) crosslinker, rendered the films insoluble in common solvents for PTMSP such as toluene. At all temperatures, mixed gas CH4 and n-C4H10 permeabilities of crosslinked PTMSP were less than those of uncrosslinked PTMSP, which correlates with lower free volume in the crosslinked material. The presence of fumed silica (FS) nanoparticles in both uncrosslinked PTMSP and crosslinked PTMSP increased mixed gas CH4 and n-C4H10 permeabilities, consistent with the disruption of polymer chain packing by such nanoparticles. Mixed gas CH4 permeabilities of all films were significantly less than their corresponding pure gas CH4 permeabilities. For example, at 35 degrees C, the mixed gas CH4 permeabilities were approximately 60-80% less than their pure gas values. The greatest decrease was observed for uncrosslinked PTMSP, while nanocomposite PTMSP films showed the least decrease. The mixed gas n-C4H10/CH4 selectivities of crosslinked PTMSP and nanocomposite PTMSP films were less than those of uncrosslinked PTMSP at all temperatures. For example, at 35 degrees C, the mixed gas n-C4H10/CH4 selectivities of uncrosslinked PTMSP, crosslinked PTMSP containing 10 wt% crosslinker, and uncrosslinked PTMSP containing 30 wt% FS were 33, 27, and 17, respectively, when the feed gas contained 2 mol% n-C4H10 and the total upstream mixture fugacity was 11 atm. For all films, as temperature decreased, mixed gas n-C4H10 permeabilities increased, and mixed gas CH4 permeabilities decreased. Consequently, the mixed gas n-C4H10/CH4 selectivities increased substantially as temperature decreased and the mixed gas selectivity of uncrosslinked PTMSP increased from 33 to 170 as temperature decreased from 35 degrees C to -20 degrees C when the feed gas contained 2 mol% n-C4H10 and the total upstream mixture fugacity was 11 atm. Published by Elsevier Ltd.