Influence of internal and external donors on activity and stereospecificity of ziegler‐natta catalysts

Abstract

Three kinds of MgC12-supported TiCI, catalysts (ester-free, ethyl benzoate (EB, monoester) and dibutyl phthalate (DNBP, diester) as internal donors) were prepared. Polymerization of propylene was carried out using these catalysts with and without phenyltriethoxysilane (PTES) as an external donor. Significant differences were observed in the kinetic behavior of polymerization among ester-free, monoester, and diester systems. Addition of PTES, however, did not change the kinetic behavior. The polymers produced were separated into three fractions by extraction with boiling heptane and octane, and the molar mass distribution (MMD) curves were measured for these three fractions. The heptane-insoluble, isotactic polymer obtained in the absence of PTES was found to consist of two fractions, octane-soluble and -insoluble. The octane-soluble polymer having lower molar mass contained appreciable amounts of syndiotactic stereoblocks in the chains, whereas the octaneinsoluble polymer did not contain such stereoblocks. Addition of PTES drastically increased the octaneinsoluble fraction without changing the average molar mass. On the other hand, the MMD curve for the heptanesoluble, atactic polymer gradually shifted to the lower molar mass range with an increase in the concentration of PTES. From these results, the effects of internal and external donors on catalyst activity and stereospecificity were discussed putting emphasis on the differences between monoesters and diesters.

The discovery and progress of MgCl2‐supported TiCl4 catalysts

“…The function of alkoxysilanes in enhancing not only the stereospecificity but also the molecular weight of the resulting PP also was reported. 27,28 Designing suitable structures of dialkyl phthalates and alkoxysilanes gave us about 1000 times higher activity than the TiCl 3 catalysts and extremely high stereoregularity that was more than 98% of I.I. Furthermore, the resulting PP did not have any regio-irregularity except for its chain end.…”

Study on the microstructures of polypropylene synthesized by a novel MgCl2-supported and low Ti-loading Ziegler–Natta catalyst

“…2 [33 -35]. As reported [13,33], Ti-species a, b could produce PPs with low isotacticity, while c, d with high isotacticity. The polymers synthesized by the equilibriums between a and c (or b and d) were of stereoblock structures.…”

Temperature Rising Elution Fractionation of Polypropylenes Produced by Heterogeneous Ziegler-Natta Catalysts Containing Different Internal Donors

“…Site-I is similar to that proposed by Soga. 5 The simultaneous coordination of aromatic diester with Ti and Mg atom forms a bridged structure, which leads to high rigidity of active sites. Such a structure also makes it not easy to be removed by AIEt 3 • The active sites may produce the most highly isotactic fractions eluted near 1 I 5°C.…”

“…4 Soga proposed a model to explain the difference of mono-and diester, in which monoester was presumed to be extracted by AlEt 3 more easily than diester. 5 In this paper, some MgC1 2 -supported Ziegler-Natta catalysts employing different ester compounds (including mono-and diesters) as internal electron donors were prepared. The polypropylene (PP) samples obtained from these catalysts were fractionated with temperature rising elution fractionation (TREF) and the influence of different internal donors on the tacticity of PPs was investigated.…”