Investigation on the dynamic crystallization and melting behavior of β-nucleated isotactic polypropylene with different stereo-defect distribution-the role of dual-selective β-nucleation agent

摘要

The selectivities of different β-nucleating agents might be quite different from each other, which is important in determining the crystallization and properties of the obtained β-isotactic polypropylene (β-iPP). However, the relationship between molecular structure and dynamic crystallization behavior of β-iPP nucleated by dualselective β-nucleating agent (DS-β-NA) is still not clear. In this study, the dynamic crystallization and melting behavior of two β-iPP with nearly same average isotacticity but different stereo-defect distribution, nucleated by a DS-β-NA (N, N'-dicyclohexyl-2, 6-naphthalenedicarboxamide; trade name TMB-5), were studied by differential scanning calorimetry, wide-angle X-ray diffraction, and scanning electronic microscopy. The results indicated that in the presence of TMB-5, the dynamic crystallization and melting behavior of the samples are quite different because the joint effects of the dual selectivity of TMB-5 and stereo-defect distribution of the iPP under different cooling rates. Two important roles were observed: (i) slow cooling rate favors the formation of high β-fraction; and (ii) high crystallization temperature favors the crystallization of α-phase accelerated by TMB-5. Generally, the dual selectivity of the DS-β-NA, the stereo-defect distribution of iPP, and the cooling rate were important factors in determining the formation of β-crystal.