Miscible blends of Matrimid and carboxylated polymers of intrinsic microporosity (cPIM-1) at the molecular level have been discovered. Their miscibility has been confirmed by polarized light microscopy (PLM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The existence of hydrogen bonding promotes compatibility between these two polymers. A good agreement between experimental and predicted data on gas permeability and selectivity is observed. The addition of cPIM-1 in Matrimid significantly enhances the plasticization pressure for all blended membranes. A small loading of 5-10 wt% of cPIM-1 in Matrimid improves the plasticization pressure from less than 10 atm-15 atm while a higher loading of cPIM-1 shifts the plasticization pressure to 20 atm. (C) 2015 Elsevier Ltd. All rights reserved.