Abstract : Herein, we demonstrate the possibility to prepare multiblock polyester-based copolymers in a “one-pot, one-step” approach from independent and simultaneous ROPs of 4- and 6-membered lactones. The independent behavior of those polymerizations appears to be possible due to the ability of 4- and 6-membered lactones to polymerize selectively by “O−alkyl” and “O−acyl” cleavages, respectively. Those two types of lactone bond ruptures have been initiated from various heterofunctional moieties bearing hydroxyl and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-based carboxylic salt functions.