Triblock copolymers consisting of poly(oxyethylene) (PEG), poly(D-lactide) (PDLA), and poly(L-lactide) (PLLA) were successfully prepared by the two-step ring-opening polymerization of D- and L-lactides via PEG-PDLA diblock copolymers. These triblock copolymers as well as the diblock copolymer PEG-PDLA and a mixture of enantiomeric diblock copolymers PEG-PDLA/PEG-PLLA were emulsified to make their aqueous micelle solutions. It was found out that the triblock copolymers and the diblock copolymer mixture can form sc crystals in the core to highly stabilize the core shell particles. In particular, the micelle of a triblock copolymer having a short middle PDLA block gave the smallest particles covered with thin layer of PEG coronas, because the sc crystals had formed around the core shell interface. These results suggested that the micelle particle morphology can be tuned by changing the core structure even at constant hydrophilic/hydrophobic balance of the block chains. (C) 2015 Elsevier Ltd. All rights reserved.