Abstract
A series of copolymers were prepared by ring-opening polymerization of e-caprolactone and DL-lactide, using zinc lactate as catalyst. The resulting PCL/PLA copolymers were characterized by various analytical techniques such as NMR, SEC, DSC and X-ray diffraction. The [CL]/[LA] ratios of the copolymers are very close to those in the feed, indicating a good conversion of monomers. The copolymers with CL contents higher than 50% appear semi-crystalline, the crystalline structure being of the PCL-type. Compression molded polymer films were allowed to degrade in a pH = 7.0 phosphate buffer containing pseudomonas lipase. Data show that copolymers with CL contents lower than 25% are not degradable and the degradation rate increases with CL content for CL-rich copolymers. Various soluble degradation products are detected in the degradation medium, including CL1 to CL3 and LA1 to LA4 homo-oligomers, and CL2LA1 co-oligomer. The presence of LA homo-oligomers and CL2LA1 co-oligomer suggests that pseudomonas lipase can not only degrades PCL, but also LA short blocks along PCL/PLA copolymer chains. On the other hand, little changes of compositions are detected during degradation, in agreement with a surface erosion mechanism as shown by ESEM.