Investigation of the stereo-defect distribution and conformational behavior of isotactic polypropylene polymerized with different Ziegler-Natta catalysts
writer：Jian Kang, Feng Yang, Tong Wu, Huilin Li, Dongming Liu, Ya Cao, Ming Xiang.
keywords：Ziegler-Natta catalysts
source：期刊
specific source：Journal of Applied Polymer Science, 2012, 4, 3076-3083.
Issue time：2012年
Two isotactic polypropylene (iPP) samples (PP-A and PP-B) were obtained by utilizing two different heterogeneous Ziegler–Natta catalysts in a given polymer- ization system. The molecular structure and conformational behavior of the samples were studied. The results of determi- nation of xylene soluble material (XS) and 13C NMR showed that the average isotacticity of the samples were nearly same. However, the results of high-resolution high-temperature 13C NMR (HRHT 13C NMR) and successive self-nucleation and annealing (SSA) fractionation revealed that the amount of high isotacticity of PP-B was lower than that of PP-A, and the amount of relative medium and low isotacticity of PP-B was higher than PP-A, indicating that the stereodefect distri- bution of PP-B was more uniform than PP-A. The calculation of average meso sequence length from SSA was found to be in good agreement with that calculated from the results of HRHT 13C NMR. Moreover, Fourier transformation infrared was utilized to study the influence of stereodefect distribu- tion on the conformational behavior of iPP. The result sug- gested that the molecular conformation of the PP-B was more disordered than PP-A, the regularity of molecular structure for PP-B was lower than that of PP-A. The related action mechanism and the influences of which on crystalliza- tion behavior were discussed