Ring-opening polymerization of PLGA-PEG diblock copolymers was studied using supercritical CO2 (SCCO2). The results of the SCCO2 method were compared with a melting procedure using a three-necked flask. A pressure of 317 bar, temperature of 132 degrees C, and time of 14 h resulted in the maximum molecular weight (10,138 g/mol) and yield (88.15 w/w %); these results were significantly higher than those for the melting method (M-w = 6664.5 g/mol, yield = 57.95 w/w %). Furthermore, the reaction time for achieving maximum M-w and yield via SCCO2 (14 h) was lower than with the melting method (24 h). The lactide-to-glycolide molar ratio and percent by weight of methoxy PEG matched well with the initial value when SCCO2 was used. The critical micelle concentration (CMC), and particle size in SCCO2 were higher than with the melting method, as the molecular weight of SCCO2 obtained using was higher.