The anionic polymerization of ethylene oxide (EO) initiated by lithium derivatives is extremely sluggish and only yields very low molar mass EO oligomers because of the low reactivity of lithium alkoxide species We show here that using the monomer-activated anionic polymerization approach one can activate the C-O-Li bonds towards EO polymerization at low temperature and in non polar media Starting from living polystyryllithium and polyisoprenyllithium addition of triisobutylaluminum (i-Bu3Al) in excess to lithium species triggers the propagation reaction of EO allowing the direct synthesis in a few hours of poly(styrene-b-ethylene oxide) and poly(isoprene-b-ethylene oxide) diblock copolymers with a molar mass of the PEO block up to 10 000 g/mol (C) 2010 Elsevier Ltd All rights reserved