Ethyl tert-butyl ether (ETBE) is considered as one of the most promising bio-fuels in Europe. During its industrial synthesis, ethanol forms an azeotropic mixture with ETBE, which cannot be separated by simple distillation. We have formerly reported several selective linear multi-block copolymer membranes for this separation by pervaporation. These multi-block copolymers offered good film forming ability and processability but their transport properties were limited by the permeability/selectivity trade-off. In this work, a new grafting strategy of multi-block copolymers is investigated, aiming at increasing membrane permeability strongly while maintaining a very high selectivity for ETBE purification. The grafted multi-block copolymers were obtained by a synthesis scheme involving step-growth polymerization, polymer functionalization and grafting by "click" chemistry. The membrane properties are discussed in terms of structure-morphology-property relationships for the sorption and pervaporation of the targeted mixture. By hindering the diffusion of the bulky ETBE molecules and ensuring high permeability for ethanol molecules, the particular morphology of the grafted multi-block copolymer membranes led to outstanding membrane separation performance for ETBE purification.