The current work describes the synthesis and mass transport properties of a series of blend membranes based on a highly permeable polyether based segmented block copolymer and a poly(ethylene glycol) based additive. This series of polymers integrates the knowledge of molecular design and molecular blending and presents CO2 permeabilities currently unknown to any polyether based block copolymer (system) known in literature. The concept presented is not limited to this specific case and hence opens a window of opportunity for further development of highly permeable block copolymer systems for CO2 separation and in particular for use in post-combustion CO2 capture. (C) 2011 Elsevier B.V. All rights reserved.