Tuning the crystalline and mesophase structure of olefin block copolymer through self-nucleation and annealing treatments

Abstract

As a type of novel semi-crystalline block copolymers, the final properties of olefin block copolymers (OBCs) greatly depend on the crystalline and phase-separated structures. In the present work, we systematically investigated the influence of self-nucleation and annealing on the lamellar and mesophase-separated structure of OBCs. According to the crystalline and melting behavior after self-nucleation and annealing treatments, four different regimes can be recognized with the self-seeding temperature T_s varying from 125 to 109 °C. In regime A, only self-nucleation occurs, while it coexists with lamellar thickening in regime B. In regime C, there is only lamellar thickening behavior. The lamellar thickening induced inconsecutive lamellar crystals observed revealed that the rearrangement of the hard blocks, which are next to the soft blocks and trapped in the intermediate regime between crystalline and amorphous phases, into neighboring lamellar crystals should be the mechanism for the lamellar thickening of the OBCs. Surprisingly, no lamellar thickening occurs and a new small melting peak appears at lower temperatures in regime D. Considering the block dispersity of OBCs, the emergence of a small melting peak at lower temperatures can be attributed to the crystallization of the ethylene sequence with relatively weaker crystallization abilities, which are not able to crystallize in a standard crystalline state. Based on these findings, we gained some new understandings on lamellar thickening behavior of OBCs and established the self-nucleation and annealing process as a powerful tool for tuning the crystalline and phase-separated structures of OBCs.