To obtain the PEO-PBLA copolymer, poly(ethylene oxide) with a methoxy group at one terminal and a primary amino group at the other terminal was used as an initiator of the polymerization of BLA-NCA. After the synthesis of the PEOPBLA block copolymer, the crude block copolymer was analyzed by GPC. The GPC chromatogram of PEO-PBLA block copolymer in THF, however, showed the presence of a trace amount of BLA oligomer in the range of 27.5 and 29.9 min retention time