Investigation of the Thermal Stability and Hydrolytic Degradation Kinetics of Poly(Lactide-co-Glycolide) Melts.

Poly(lactide-co-glycolide) (PLGA) is widely used in a variety of long-acting injectables. However, its biodegradable nature creates potential chemical stability challenges during melt extrusion, where PLGA is exposed to elevated temperature (100-140 °C) for several minutes. This study evaluated the thermal stability of three PLGA grades (Resomer® 502, 502H, and 505) with varying molecular weights and chain-ends using a differential scanning calorimeter and twin-screw extruder. DSC results revealed that both residual water content and chain-end groups significantly accelerate PLGA degradation. At 0.2% water content, all samples maintained good stability (less than 15% reduction in molecular weight). However, at 0.4% water content, Resomer 502H, which has acid end groups, experienced significant degradation (45% reduction in molecular weight) after 30 min at 140 °C due to catalyzed hydrolysis. The extruded samples remained stable across tested barrel temperatures (100 °C and 140 °C) and screw speeds (125 and 250 rpm). Further investigations of PLGA with 0.2% water content demonstrates that the hydrolysis rates of Resomer® 502 and 505 were comparable, indicating that molecular weight does not influence hydrolysis rate. In contrast, Resomer® 502H exhibited a higher hydrolysis rate and a slightly higher activation energy, suggesting a greater temperature dependency. Additionally, when subjected to 200 °C for one hour with less than 0.03% water content, Resomer® 505 showed a less than 7% reduction in molecular weight, indicating minimal thermal degradation. Conversely, Resomer® 502 and 502H experienced an increase in molecular weight, which was likely attributed to recombination reactions, particularly in Resomer® 502H, which has higher tin content (170 ppm).