The purpose of this study is to investigate copolymerization of glycolide and e-caprolactone and to understand correlationship between the thermal properties and microstructure of the copolymers (av. block lengths, sequence analysis, extent of transesterification) by using DSC, NMR spectroscopy and wide-angle X-ray diffraction (WAXD).
The relationship betweeen microstructure and thermal properties in P(GL/CL) with various GL/CL compositions was investigated. Bulk polymerization was carried out in an ampoule in the presence of Sn-oct as catalyst. The glass transition temperature of the copolymers proportionally ranged between -58.2℃ and 39.7℃ with varying GL composition. However, melting temperature of the copolymers varied unproportionally with their composition. In 60 ~100 mole % GL compositions of the copolymers, there are no changes in melting temperature and solvent characteristics. In this range, the average block length of glycolyl units is more than 3.5 units and that of caprolactone units is less than 1.5 units. The copolymers, which have 3.5 units of glycolyl structure, maintain crystal structure and show melting and solvent characteristics similar to homo polyglycolide. In 30~50 mole % GL compositions, there is no crystal melting transition. The average block lengths of glycolyl and caprolactone units are 1.5~2.6 and 1.3~1.8 units respectively. Especially, GL5.0/CL5.0 copolymer shows thermo-plastic elastomer characteristics. In 0~20 mole % GL compositions of copolymers, the range of melting points is 23℃~58℃ In this range, the average block length of caprolactone units is increased.
We can control the average block length of glycolyl units by changing polymerization parameters such as reaction temperature and catalyst/initiator concentration. As the reaction temperature increases, the average block length of glycolyl units becomes shorter due to the transesterification. As lower the mole concentration of catalyst/initiator, that of glycolyl units becomes longer.