Metal-organic framework 5 (MOF-5) nanocrystals with a high surface area (3000 m(2)/g) and high thermal stability (up to 400 degrees C) were synthesized and added to Matrimid (R) to form mixed-matrix membranes for gas separations. Scanning electron microscopy (SEM) images of the membrane cross-sections revealed significant plastic deformation of the polymer matrix owing to the strong affinity between the MOF-5 and Matrimid (R). At 30% MOF-5 loading, the permeabilities of the gases tested increased 120% while the ideal selectivities remained constant compared to Matrimid (R). Residual gas analysis of permeates of gas blends with different mixture ratios revealed an increase in selectivity for CH4. (c) 2008 Elsevier B.V. All rights reserved.