Polymerization control and fast characterization of the stereo-defect distribution of heterogeneous Ziegler-Natta isotactic polypropylene

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 (Basel!), the cocatalyst/external donor (triethylaluminium/dicyclopentyldimethoxysilane. Al/Si) mole ratio was gradually changed from 30 to 36, accompanied with hydrogen adjustment. And we obtained a series of iPP samples (A-E). The characterization of C-13 NMR, xylene soluble fraction (XS) showed the average isotacticity of the obtained samples are nearly same, but the results of high resolution C-13 NMR, temperature rising elution fractionation (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) fractionation 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 C-13 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. (C) 2011 Elsevier Ltd. All rights reserved.