Characterization of the effects of the C/N mixed external donors on the stereo-defects distribution of polypropylene by successive self-nucleating and annealing and 13C-NMR techniques
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As the external donor in Ziegler-Natta catalysts have an important influence on the stereo-defects distribution of polypropylene, the effects of the mixed external donors (the mixture of Donor-C (cyclohexylmethyldimethoxysilane) and Donor-N (n-propyltriethoxysilane) ) on the isotactic sequence length and its distribution of polypropylene prepared by Ziegler-Natta catalyst through propylene bulk polymerization were studied through the Successive self-nucleating and annealing (SSA) and 13C-NMR techniques. The SSA results showed that the relative contents of the highest isotactic component and the lamellar thickness in the polypropylene chain gradually increased with the increase of the relative component of Donor-C in the C/N mixed external donors, indicating the isotactic sequence length of polypropylene got longer, and the lamellar thickness distribution of polypropylene became broader, revealing the isotactic sequence length distribution of polypropylene got broader. In addition, the 13C-NMR results showed that the average meso isotactic sequence length (MSL) of polypropylene gradually increased with the increase of the content of Donor-C in the C/N mixed external donors, which was in good coincident with the results calculated from SSA, showing a good correspondence between the SSA and 13C-NMR techniques.
KeywordsPolypropylene Mixed external donors Lamellar thickness Isotactic sequence length Successive self-nucleation and annealing
The authors express thanks for the supports of the National Science Foundation of China (No. 51073170).
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