effect of the combined external donors on the stereo defect distribution and microstructural properties of polypropylenes synthesized with an industrial ziegler natta catalyst

Homopolypropylene samples with an industrial Ziegler-Natta catalyst and in the presence of combined external donors, namely cyclohexyldimethoxymethylsilane (donor C) and Dicyclopenthyldimethoxysilane (donor D) with different molar ratio of donor C to D (0.3 for sample 1, 1.2 for sample 2, 4.6 for sample 3) were synthesized. A synergistic effect on molecular weight and approximately on poly dispersity index and melting temperature, decrease in crystallinity (%) and crystallization temperature from sample 1 to 3 were observed. The SSAresults showed that in spite of close average stereo-regularity, the stereo-defect distribution differences between the all of samples were so vast and from sample 1 to 3, thick lamellar amount was changed drastically and stereo-defect distribution became narrower. With using mixed external donors, different properties like high molecular weight, broad PDI and narrow stereo- defect distribution in sample 3 and low molecular weight, narrow PDI and broad stereo-defect distribution in sample 1 were obtained.

کلیدواژه ها:

isotactic polypropylene ، external electron donor ، ziegler-natta catalyst ، stereo defect distribution ،