Preparation and Characterization of ABA-Type Poly(l-Lactide-co-ε-Caprolactone) Block Copolymers.

In this study, poly(l-lactide-co-ε-caprolactone) (PLCL) block copolymers with an ABA structure were prepared using a two-step polymerization process, and their microstructures, thermal, and mechanical properties were systematically investigated based on the introduction of ε-caprolactone as a comonomer in the first step to form the B block. As a result, it was observed that as the content of the B block, or the ε-caprolactone comonomer increased, the average sequence length of l-lactide decreased, indicating that a potential impact on the crystallization behavior and thermal properties of the final PLCL block copolymers. However, the decrease in thermal properties, such as the melting temperature, was less significant than expected. For instance, the melting temperature of pure PLA in this study was 172.5 °C, whereas the PLCL block copolymer with 9 mol% ε-caprolactone comonomer had a melting temperature of 171.1 °C, showing a relatively minimal difference between the two samples. Additionally, as the ε-caprolactone content increased, tensile strength and initial modulus of the PLCL block copolymer slightly decreased, while the breaking strain significantly increased. This suggests that the two-step polymerization method proposed in this study is effective in imparting flexibility to PLA while minimizing its mechanical property degradation. Consequently, the introduction of comonomer such as the ε-caprolactone through controlled polymerization process offers valuable insights for developing PLA materials with diverse properties. [ABSTRACT FROM AUTHOR]