In Europe, ethyl tert-butyl ether (ETBE) is currently considered as one of the most promising bio-fuels when it is obtained from bio-ethanol. Nevertheless, its industrial synthesis process leads to an azeotropic mixture containing 20wt% of ethanol which has to be removed for fuel applications. In this work, new graft copolymers cellulose acetate-g-poly(methyl diethylene glycol methacrylate) are considered for the purification of ETBE by pervaporation. Two families of graft copolymers; were investigated with almost the same copolymer graft contents but short or long highly permeable grafts. Their properties are discussed in terms of structure-property relationships for the sorption and pervaporation of the targeted azeotropic mixture. It is shown that the sorption properties are mainly governed by the copolymer graft content. On the other hand, the pervaporation features are strongly influenced by the copolymer graft content and architecture. For the same copolymer graft contents, it appears that the copolymers with short grafts are more selective and less permeable than the copolymers with long grafts. This difference in permeation behaviour is ascribed to different copolymer microstructures. The less segregated short grafts are more constrained within the rigid cellulose acetate matrix and lead to pervaporation separation factors that are twice those of the corresponding copolymers with long grafts. A comparison with the related literature results also shows that these graft copolymers are amongst the best materials so far reported for the separation of the azeotropic mixture ETBE/EtOH and this approach appears really promising for the design of a wide range of new copolymers with outstanding features for this application. (C) 2009 Elsevier B.V. All rights reserved.