Liquid–solid transition in mesophase separated olefin multiblock copolymers during crystallization

Abstract

The effect of block structure on the liquid–solid transition (LST) of ethylene–octene multiblock copolymers (OBCs) during isothermal crystallization has been investigated by rheology, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). Due to the mesophase separation in OBC melts, the formation of a critical network at the LST in the OBCs with low crystallinity (7–14 wt%) was found to be different from that in homogeneous systems. The viscoelastic properties at the LST in the heterogeneous OBCs suggested a slower relaxation behavior of the critical network, and the liquid–solid transition in strongly segregated OBCs was observed to occur in the intermediate or even late stage of crystallization, demonstrated by the much higher crystallinity and large spherulites at the LST. The delayed liquid–solid transition has been discussed and can be attributed to the initial confinement of the hard-block domains in the nucleation and growth of the crystals.