Structure-property relationships of copolymers obtained by ring-opening polymerization of glycolide and epsilon-caprolactone. Part 1. Synthesis and characterization

A series of copolymers with various compositions were synthesized by bulk ring-opening polymerization of glycolide and c-caprolactone, using stannous (II) octoate or zirconium (IV) acetylacetonate as initiator. Reaction time and temperature were varied so as to induce different chain microstructures. The resulting copolymers were characterized by H-1 NMR, SEC, DSC, and X-ray diffraction. The average lengths of glycolyl (L-G) and caproyl sequences (L-C) and the degree of randomness (R) were calculated and compared to the values of completely random chains. The concentration of CGC sequences was also obtained which resulted from transesterification reactions. Data showed that stannous (II) octoate leads to less transesterification than zirconium (IV) acetylacetonate, and lower temperatures lead to less transesterification than higher ones. The copolymers exhibited a more or less blocky chain structure because of the reactivity difference between glycolide and E-caprolactone. The crystalline structure and thermal properties depend on both the composition and the chain microstructure. PGA- and PCL-type crystallites were obtained for copolymers with intermediate compositions.