Reversible Lamellar Periodic Structures Induced by Sequential Crystallization/Melting in PBS-co-PCL Multiblock Copolymer

Reversible periodic structures in a symmetric poly(butylene succinate)-co-poly(e-caprolactone) (PBS-co-PCL) multiblock copolymer have been detected for the first time. A phase-segregated structure can be observed under the phase contrast optical microscope at 150 °C, but it has no significant effect on the subsequent crystallization behavior of the PBS component, which can break out at lower temperatures (i.e., 82 °C) forming spherulites that contain the molten PCL component within them. During PBS chains crystallization at 82 °C, two peaks are detected by SAXS experiments. The high-q peak corresponds to a periodic structure formed within PBS-rich domains consisting of PBS lamellae and amorphous regions containing PBS and molten PCL chains. The low-q peak arises from a periodic structure formed within PCL-rich domains consisting of PBS lamellae and thick amorphous layers needed to accommodate the large fraction of molten PCL chains at 82 °C. When the temperature is decreased to 36 °C, the PCL component cr...