Abstract
A series of copolymers were synthesized by ring opening polymerization of glycolide, L-lactide and ε-caprolactone, using zirconium (IV) acetylacetonate (Zr(Acac)4) or stannous octoate (Sn(Oct)2) as catalyst. The resulting terpolymers were characterized by analytical techniques such as 1H NMR, SEC, and DSC. Data confirmed that Sn(Oct)2 leads to less transesterification of polymer chains as compared to Zr(Acac)4 under similar conditions. The various copolymers were compression molded and allowed to degrade in a pH 7.4 phosphate buffer at 37oC. The results showed that the degradation rate depends not only on the copolymer composition but also on the chain microstructure, Sn(Oct)2 initiated copolymer degrading less rapidly than Zr(Acac)4 initiated ones with more random chain structures. The caproyl component appeared the most resistant to degradation as its content increased in almost all cases. Moreover, caproyl units exhibit a protecting effect on neighboring lactyl or glycolyl units. The glycolyl content exhibited different features: it decreased due to faster degradation of glycolyl units which are more hydrophilic than caproyl and lactyl ones, or remained stable in the case of abundant C-G-C sequences which are very resistant to degradation, or even increased due to formation of PGA crystallites. Terpolymers could crystallize during degradation if the block length of one of the components is sufficiently long, even though they were amorphous initially.