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Abstract Summary: Films of poly( L ‐lactic acid) (PLLA) and copolymers of L ‐lactide (LLA) with either glycolide P(LLA‐GA)(81/19) or D ‐lactide P(LLA‐DLA)(77/23) were prepared and an effect of comonomer type on the hydrolytic degradation of the films was studied in phosphate‐buffered solutions at 37 °C. The degraded films were investigated using gravimetry (weight loss and water absorption), gel permeation chromatography, DSC, X‐ray diffractometry, tensile testing and polarization optical microscopy. To exclude the effects of molecular weight and crystallinity on hydrolytic degradation, the films were prepared from polymers with similar molecular weights and were made amorphous by melt quenching. It was found that the hydrolytic degradation rate decreased in the order P(LLA‐GA) > P(LLA‐DLA) > PLLA. The hydrolytic degradation rate constant of PLLA and LLA copolymer films increased with increasing the water absorption (hydrophilicity), or with decreasing the initial glass transition temperature or the L ‐lactyl unit sequence length, indicating that the hydrolytic degradation rate of the copolymers was closely related to these three parameters. The crystallization of P(LLA‐GA) film occurred within hydrolytic degradation for 20 weeks. M n of PLLA and LLA copolymer films as a function of hydrolytic degradation time. magnified image M n of PLLA and LLA copolymer films as a function of hydrolytic degradation time.
Saha et al. (Wed,) studied this question.