BIODEGRADABLE LACTONE COPOLYMERS .2. HYDROLYTIC STUDY OF EPSILON-CAPROLACTONE AND LACTIDE COPOLYMERS

Copolymers of epsilon-CL/L-LA and epsilon-CL/DL-LA were allowed to age in a buffer solution of pH 7 at 23 and 37 degrees C. The effects of t ime and temperature on the rate of hydrolysis were examined by various techniques including weighing (water absorption and weight loss), SEC (molecular weight and polydispersity), and DSC (thermal properties). For comparison, the hydrolytic behavior of PLLA, PDLLA, and commercial PCL homopolymers was investigated by the same methods. SEC measuremen ts showed that molecular weights of the copolymers and PLA homopolymer s started to decrease during the first week of hydrolysis, but signifi cant mass losses occurred only much later. As expected, there was no c hange in either molecular weight or mass of PCL during the hydrolysis study. The kinetic results for copolymers and homopolymers were calcul ated to study the degradation mechanism. During hydrolysis, the crysta llinity of the initially semicrystalline copolymers increased and some crystallinity appeared in the initially amorphous L-LA-containing cop olymers. (C) 1996 John Wiley & Sons, Inc.