Polymerization control and fast characterization of the stereo-defect distribution of heterogeneous Ziegler-Natta isotactic polypropylene
writer：Jian Kang, Feng Yang, Tong Wu, Huilin Li, Ya Cao*, Ming Xiang*
keywords：polymerization, stereo-defect distribution
source：期刊
specific source：European Polymer Journal 2012, 48, 425-434.
Issue time：2012年
Adjustment of the stereo-defects distribution of isotactic polypropylene (iPP) is important for obtaining better properties of the resins in Ziegler–Natta polymerization. In this study, in order to adjust the stereo-defect distribution of iPP prepared by the Spheripol process (Basell), the cocatalyst/external donor (triethylaluminium/dicyclopentyldimethoxysilane, Al/Si) mole ratio was gradually changed from 30 to 36, accompanied with hydrogen adjust- ment. And we obtained a series of iPP samples (A–E). The characterization of 13C NMR, xylene soluble fraction (XS) showed the average isotacticity of the obtained samples are nearly same, but the results of high resolution 13C NMR, temperature rising elution frac- tionation (TREF) and xylene solvent fractionation indicated that, as the Al/Si ratio increases, the amount of high isotacticity in iPP gradually decreases, the amount of medium and low isotacticity gradually increased, the distribution of stereo-defects becomes more uniform.
A relative time-saving method, successive self-nucleation and annealing (SSA) fraction- ation was applied to evaluate the stereo-defect distribution of iPP. A calibration which can be used to convert SSA final melting curves to the average meso sequence length curves was constructed. A good agreement between 13C NMR, XS, TREF results and SSA fractionation results indicated that it is feasible by using SSA to provide quick characterize of the stereo-defect distribution of iPP.