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Full quantum chemical calculations, using density functional theory (DFT), have been conducted to explain the effect of donors on the 'activation mechanism' in the Ziegler-Natta (Z-N) catalyst system. In the activation mechanism, the inactive TiIVCl4 catalyst converts into the active TiIIICl2Et catalyst with the help of the AlEt3 present in the system. The donors that have been considered in this study are: ethyl benzoate ( eb), two representative diether cases, a phthalate donor, and a silyl ester donor. The results indicate that eb and the diether donor cases donor have a negative effect on the barriers for the activation mechanism. However, the eb donor can be displaced from the MgCl2 surface by AlEt3, which matches experimental observations. For the phthalate, silyl ester and TiCl3-OC4H8Cl cases, the results indicate that a significant induction period would be present in Z-N systems employing such donors or having such a catalytic center, before catalysis could commence. [ABSTRACT FROM AUTHOR]

The development of new donors (Lewisbases, usually containingoxygen atoms) is one of the chief areas of research in Ziegler–Natta(ZN) olefin polymerization systems. The addition of such donors hasled to improvement in the activity and selectivity of ZN systems.However, in order for the donor to be effective, it has to be chemicallystable and resistant to decomposition by Lewis acidic species suchas AlEt3. Discussed in the current work is the chemicalstability of different ester donors, including aromatic benzoate donorsand the silyl estera promising new donor class in ZN systems.Full quantum chemical calculations with density functional theory(DFT) indicate that esters can undergo decomposition through differentpathways upon interaction with species such as the AlEt3dimer: Al2Et6. Moreover, the studies showthat the active, supported titanium catalyst species can cause donordecomposition and, in fact, is likely to be the greater threat todonor decomposition than Al2Et6. This explainswhy the addition of excess donors can lead to the poisoning of theactive site in ZN systems. We have also computationally investigatedmeans of improving the silyl ester donors in order to make them morerobust and resilient to donor decomposition by Al2Et6and the supported active titanium species. [ABSTRACT FROM AUTHOR]