Shear-induced crystallization of olefin multiblock copolymers: Role of mesophase separation and hard-block content

Abstract

Shear-induced crystallization of olefin block copolymers (OBCs) with different molecular weights and contents of hard-block was investigated by a recently suggested suspension-based rheological method. The volume fraction of crystals from this method does not exhibit frequency dependency, which was a typical shortcoming of traditional rheological studies on polymer crystallization. Besides, the nucleation rate and agglomeration of crystals can be quantified through the decomposed dynamic moduli. Weak preshear flow has different influences on the crystallization of OBCs, depending on the extent of mesophase separation and the content of hard-block. The acceleration of crystallization, represented by the half crystallization time, can be well described by the effective specific work, which integrates the contributions from molecular weight and the mesophase separation. For strong phase-separated OBCs, preshear accelerates crystallization through faster nucleation without changing the maximum nucleation rate and the agglomeration of crystals. For homogeneous and weak phase-separated OBCs, the maximum nucleation rate increases, and the agglomeration decreases with the effective specific work. Such influence of preshear becomes stronger in copolymers with a higher content of hard-block.