Effects of Temperature and pH on the Degradation of Poly(lactic acid) Brushes

Poly(lactic acid) (PLA) brushes were prepared through surface initiated ring-opening polymerization of l-lactide. Their degradation (depolymerization) was characterized by tracking their ellipsometric thickness as a function of time by repeated emersion from buffered, aqueous solutions. The pH and temperature both had a large effect on the rate of degradation. PLA brushes do not degrade in a manner similar to that of bulk PLA. Several experiments were performed, the results of which suggest that intramolecular transesterification (backbiting) was the pathway for the degradation of the PLA brush in basic, aqueous solution, similar to what has been observed for the depolymerization of PLA oligomers in basic solution. The PLA brushes degrade very slowly in acidic solution. This behavior is similar to the degradation of PLA oligomers in acidic solution.