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ABSTRACT:The morphological and kinetic characteristics of novel Ziegler-Natta catalysts were studied. Catalysts were prepared by Borealis Polymers Oy using a new synthesis technique (emulsion technology). Video microscopy was used to study the growth of single catalyst particles during polymerization in the gas and liquid phases. The distribution of single particle activity was very narrow in the catalyst without external support and was rather broad in the the silica-supported catalyst. Video microscopy of molten polymer particles allowed observation of the process and degree of fragmentation of the catalyst particles. A correlation between the activation period during the initial stage of polymerization and catalyst fragmentation was found. Fragmentation was faster and more uniform with the catalyst without external support than with the silica-supported catalyst. Scanning electron microscopy provided information on morphology evolution and shape replication of the catalyst particles. With the catalyst without external support, good shape replication was observed, and compact and spherical particles were formed. With the silica-supported catalyst, shape replication was poor, and nonspherical porous polymer particle were formed. Modeling of the kinetics of propylene polymerization was done using a simple threestep reaction scheme neglecting mass and heat transport effects.

We describe a concept for modeling structural defects in crystalline magnesium dichloride used as a support in the Ziegler–Natta polymerization catalysis. The defects are systematically generated into the catalytically relevant (104) and (110) MgCl2 surfaces and stabilized by methanol, selected as a model electron donor. Periodic quantum chemical calculations indicate a strong effect of surface site coordination on the relative stabilities of both ideal and defect surfaces, favoring sites with five-coordinate magnesiums. Saturation of the surfaces by the donor completely reverses the stability order in comparison to the plain surfaces, ending up favoring four-coordinate magnesium atoms. The approach can be readily expanded to include more complex donors as well as titanium chlorides.

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