New insights into the hydrolytic degradation of poly(lactic acid): participation of the alcohol terminus

The hydrolytic degradation of monodisperse lactic acid oligomers was studied in vitro to gain insight into the degradation of oligolactic acid grafted to dextran, which we use for the preparation of hydrogels based on physical interactions, or the degradation of PLA/PLGA. The decrease in the amount of oligomer and the formation of degradation products was monitored by HPLC and MS. The amount of lactic acid oligomer decreased according to pseudo-first-order kinetics and was dependent on the dielectric constant of the medium and the pH. The OH end group was found to play a crucial role in the hydrolytic degradation; when the OH was blocked no significant degradation was observed. At acidic pH, hydrolysis was shown to proceed by chain-end scission whereas in alkaline medium, lactoyl lactate was split off. The possible consequences of these findings for the degradation of PLA matrices are discussed.