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 (Basell), 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 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 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 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.

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► We produce five iPP samples with slightly varied Al/Si ratios.
► We investigate the stereo-defect distribution of the samples in detail.
► We improved the use of SSA on the stereo-defect distribution of iPP.
► Slight increase of Al/Si ratio makes the distribution of stereo-defects more uniform.