Two series of copolymerizations of ℓ-lactide and ε -caprolactone were performed with different catalysts (antimony trioxide and stannous octoate) and chemical microstructures of the obtained copolymers(P(ℓLA-co-εCL)) were investigated by $^{13}$C NMR spectroscopy. The comonomer sequence distribution within the copolymer chain including the new sequence resulting from the transesterification reaction was analyzed with relative signal intensity of each triad sequence.
Stannous octoate catalyst leads to the copolymer which has more blocky microstructure, whereas antimony trioxide results in the copolymer with more random sequence distribution due to the higher transesterification character than Sn-catalyst.
The differences in the crystallization and the glass transition behaviors between two series of copolymers were due to the differences in copolymer microstructures. Stannous octoate catalyzed samples revealed the higher crystallizability than the samples prepared with antimony trioxide catalyst because of having the more blocky microstructure. The copolymers synthesized with antimony trioxide were highly amorphous and showed homogeneous phase structure due to random sequence distribution of the comonomer units.