In this study, composite polyetheramine (PEA)-polyhedral oligomeric silsesquioxane (POSS) membranes were successfully fabricated for carbon dioxide/hydrogen (CO2/H-2) and carbon/nitrogen (CO2/N-2) separation. The organic functional groups on the POSS cage and its small particle size enhanced its compatibility with PEA. With the optimized conditions for membrane fabrication, a uniform distribution of POSS particles across the membranes could be observed from the SEM-EDX analysis. With the weight ratio of PEA: POSS 50:50, the crystallinity of the membranes is significantly suppressed as observed in the reduction of the melting point to 2.6 degrees C, compared with the original PEA melting point of 37.4 degrees C. In addition, the mechanical strength of the soft PEA is enhanced. A high CO2 permeability of 380 Barrer with a moderate CO2/N-2 selectivity of 39.1 and a CO2/H-2 selectivity of 7.0 are achieved at 35 degrees C and 1 bar for PEA:POSS 50:50 membrane. The relationship between gas transport properties and membrane composition is elucidated in terms of PEA/gas interaction and nanohybrid structure. Fundamental study on the effect of temperature and pressure on the performance of the membranes were also carried out. The gas permeability through the membrane is found to increase at the expense of selectivity with the increase in temperature. At higher upstream gas pressure during permeation tests, improvements are observed in both CO2 permeability and ideal CO2/H-2 and CO2/N-2 selectivity due to the plasticization effect of CO2. The CO2/N-2 selectivity of the membrane is found to decrease considerably under the binary mixture because of competitive sorption between CO2 and N-2 in the membranes. (C) 2011 Elsevier B.V. All rights reserved.