To improve gas separation properties of membranes, the current research trend is to design mixed matrix membranes using various types of nanoparticles. But to be efficient, such particles must be used with already highly selective (alpha > 40), highly permeable polymeric matrixes (P > 100 Barrer). In that context, we report the results obtained with a series of copolyetherimide polymers (PEI). This polyimide series has two main advantages: it exhibits a high CO2 selectivity associated to a rubbery copolymer. Thus it has the basic requirements to be a good polymer matrix for the preparation of mixed matrix membrane. This new series was prepared with different types of polyoxyether blocks (PEO) using several aromatic monomers and diamines containing polyethyloxide and polypropyloxide moieties. Permeability measurements showed that the membranes with an ether content of 80% exhibited permeabilities of 622 and 14 Barrer for CO2 and N-2, respectively, giving rise to a high ideal selectivity of CO2 over N-2 (alpha = 44). The introduction of the propyl side groups in PEI led to linear increases in the permeability when the PEO content was increased. This trend was observed because the presence of propyl groups prevents the crystallization of PEO chains, as often reported in the literature for PEO-based membranes. (C) 2016 Elsevier B.V. All rights reserved.