Nonreversible Enhanced Crystallization of Olefin Block Copolymer Induced by Preshearing

In this work, the influence of preshearing on crystallization of olefin block copolymer (OBC) was systematically investigated. It was found that upon an interval of melt preshear the crystallization rate of OBC was prominently elevated which was evidenced by both nonisothermal and isothermal crystallization results. The lamellar thickness of OBC increased and the size of spherulites decreased after shear. Interestingly, annealing and multiple heating and cooling experiments demonstrated that the enhancement effect on crystallization was nonreversible. The morphology observations suggested that preshearing caused an alteration in mesophase structure of OBC. On the basis of our results, we speculated that the increase in the amount of hard blocks that dissolved in the soft-block-rich matrix induced by shear promoted the unique "pass-through" crystallization process of OBC, which should be responsible for the largely enhanced crystallization of sheared OBC.