The Crystallization and Melting Behaviors of PDLA-b-PBS-b-PDLA Triblock Copolymers

In this study, the poly(D-lactide)-block-poly(butylene succinate)-block-poly(D-lactide) (PDLA-b-PBS-b-PDLA) triblock copolymers with a fixed length of PBS and various lengths of PDLA are synthesized, and the crystallization behaviors of the PDLA and PBS blocks are investigated. Although both the crystallization behaviors of PBS and PDLA blocks depend on composition, they exhibit different variations. For the PDLA block, its crystallization behaviors are mainly influenced by temperature and block length. The crystallization signals of PDLA block appear in the B-D 2-2 specimen, and these signals get enhanced with PDLA block length. The crystallization rates tend to decrease with increasing PDLA block lendth during crystallizing at 90 and 100 °C. Crystallizing at higher temperature, the crystallization rates increase at first and then decrease with block length. The crystallization rates decrease as elevating the crystallization temperature. The melting temperatures of PDLA blocks increase with block lengths and crystallization temperatures. For the PBS block, its crystallization behaviors are mainly controlled by the nucleation and confinement from PDLA block. The crystallization and melting enthalpies as well as the crystallization and melting temperatures of PBS block reduce as a longer PDLA block has been copolymerized, while the crystallization rates of the PBS block exhibit unique component dependence, and the highest rate is observed in the B-D 2-2 specimen. The Avrami exponent of PBS crystallites is reduced as a longer PDLA block is incorporated or the sample is crystallized at higher temperature. This investigation provides a convenient route to tune the crystallization behavior of PBS and PLA.