Quantitative analysis of ester linkages in poly(DL-lactide) and poly(DL-lactide-co-glycolide)

A quantitative analytical method for determination of intact ester linkages in biodegradable poly(DL-lactide) (PLA) and poly(DL-lactide-co-glycolide) (PLGA) has been developed. The polymer backbone ester bonds were converted to amides by a facile reaction with n-butylamine under ambient conditions. The resulting amides were analyzed by gas chromatography. The amidation of both types of ester bonds was quantitative; reaction of the glycolate and lactate linkages was completed within 3 and 8 h, respectively. The method was free from interferences by lactic or glycolic acids and was tolerant of extraneous water. The values determined by this method were within 5% of those obtained by H-1-NMR. Application to the study of the hydrolysis of poly(DL-lactide-co-glycolide) was demonstrated where the degradation profiles of the glycolide and lactide linkages were simultaneously determined.