Investigation of the stereodefect distribution and conformational behavior of isotactic polypropylene polymerized with different Ziegler–Natta catalysts

Two isotactic polypropylene (iPP) samples (PP-A and PP-B) were obtained by utilizing two different heterogeneous Ziegler–Natta catalysts in a given polymerization system. The molecular structure and conformational behavior of the samples were studied. The results of determination 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 distribution 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 distribution on the conformational behavior of iPP. The result suggested 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 crystallization behavior were discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012