Poly(1-trimethylsilyl-l-propyne) (PTMSP) has been crosslinked using 3,3'-diazidodiphenylsulfone to improve its solvent resistance. This study reports the influence of crosslinker content on the solubility properties of PTMSP, its density, and its gas sorption and transport properties. Crosslinking PTMSP renders it insoluble even in excellent solvents for the uncrosslinked polymer. Gas permeability and fractional free volume (FFV) decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PTMSP was due to decreases in diffusion coefficients. Permeability reductions due to crosslinking could be offset by adding nanoparticles to the films. The addition of 30 wt.% fumed silica nanoparticles increased the permeability of crosslinked PTMSP by approximately 80%. In mixed gas permeation experiments, when the composition of the feed gas was 98 mol% CH4 and 2 mol% n-C4H10, uncrosslinked PTMSP had an n-C4H10/CH4 selectivity of 31 and an n-C4H10 permeability of 114,000 barrers at 35 degrees C and 14 atm feed fugacity. At the same conditions, crosslinked PTMSP containing 5 wt.% crosslinker had an n-C4H10/CH4 selectivity of 28 and an n-C4H10 permeability of 73,000 barters, and crosslinked PTMSP containing 5 wt.% crosslinker and 30 wt.% fumed silica nanoparticles had an n-C4H10/CH4 selectivity of 21 and an n-C4H10 permeability of 110,000 barters. (c) 2007 Published by Elsevier Ltd.