Effect of Copolymer Composition and Molecular Weight on Poly(Lactic-Co-Glycolic Acid) Degradation in Natural Seawater

The degradation behavior of poly(lactic-co-glycolic acid) (PLGA) under natural seawater conditions has been less systematically described than that in buffered laboratory media. In this study, PLGA copolymers with different lactic acid/glycolic acid (LA/GA) ratios were prepared at two molecular-weight levels and immersed in natural seawater. Water uptake, mass retention, molecular weight changes, glass transition temperature ( T g ) changes, and surface morphology were analyzed. PLGA-9010 exhibited limited hydration, modest T g variation, and relatively slow molecular-weight reduction, whereas PLGA-5050 showed pronounced T g depression toward seawater temperature accompanied by accelerated molecular-weight decay and earlier surface disruption. PLGA-7030 displayed intermediate behavior. Within the investigated molecular weight range, lower molecular weight samples showed slightly faster decreases in molecular weight and T g during the early stage of immersion; however, the relative degradation behavior among different PLGA compositions remained unchanged. These results provide comparative information on the degradation behavior of PLGA copolymers with different compositions and molecular weights under natural seawater conditions.