AbstractReduction of CO2 emission caused by fossil fuel power plants is widely appreciated task. The most suitable materials for off-gas membrane separation process are poly(ethylene glycol) containing polymers. Pebax® 1657 blended with low molecular weight poly(ethylene glycol)s is a promising material for the selective layer of thin film composite gas separation membranes. Stability of blend Pebax® 1657 thick membranes was evaluated at temperatures up to 90 °C, exceeding those at a stack of power plant. The membranes were tested for gas transport properties by thermoanalytical methods. It was found that a threshold of molecular weight exists between 350 and 500 g/mol, at which leaching out of the low molecular weight poly(ethylene glycol) compound from the polymer matrix becomes minimal. Poly(ethylene glycol) with methyl end groups having a molecular weight of 500 g/mol provides a blend material with a CO2 permeability coefficient higher than in case of Polyactive™. PEBAX®/DM500 blend can be a cheaper alternative to tailor made Polyactive™ in large scale production of CO2 selective thin film composite membrane.