EFFECT OF MESOPHASE SEPARATION ON THE CRYSTALLIZATION DYNAMICS OF OLEFIN BLOCK COPOLYMERS

Abstract

The present study examined the effect of mesophase separation on the crystallizaiton behavior of olefin block copolymer(OBC).Two OBCs with different ΔC8(octene content difference between the soft and hard segments) were chosen,which were shown to have different phase and crystallization morphology in the solid state.The melt morphology was further examined by rheology.The isothermal crystallization dynamics of OBCs was investigated by differential scanning calorimetry(DSC).The morphology of OBCs after isothermal crystallization was observed utilizing an atomic force microscope(AFM).The results showed that the both the two OBCs exhibited mesophase separation well above the melting temperature.Upon isothermal crystallization,the OBC with higher ΔC8 kept the mesophase separated morphology,while the OBC with lower ΔC8 displayed random distributed lamellar structure.Both the two OBCs had Avrami parameter n ≈ 3,indicating that crystallization of OBC with mesophase separation exhibited a three dimensional spread manner.This striking phenomenon was attributed to the "phase mixing" in OBCs.Some shorter crystalline hard segments can dissolve in the amorphous soft phase,which can transfer the growth of crystals into adjacent hard segment domains upon crystallization.