Different crystallization behavior of olefin block copolymer in α- and β-polypropylene matrix

The crystallization behavior of olefin block copolymer (OBC) in α- and β-polypropylene (PP) matrix was comparatively investigated. According to the DSC results, the crystallization temperature of OBC (TcOBC) is 107.9 °C, while for various PP blends containing 10 wt% of OBC, these values in α- and β-PP/OBC blends are 113.1 °C and 99.2 °C, respectively. Unlike the elevated TcOBC value in α-PP/OBC blend, the TcOBC value in the β-PP based counterpart is decreased compared to that in neat OBC, indicating inhibited crystallization. Structural investigations revealed that the inhibited crystallization of OBC in β-PP may be related to the unique crystalline structure of β-PP matrix. The more loosely arranged interfibrillar region in β-PP matrix is capable of accommodating OBC hard blocks and inducing finer dispersion of OBC, which may lead to fewer OBC crystallization nuclei in each OBC micro-domain, and consequently the slower crystallization of OBC in β-PP matrix.