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DFT molecular modeling studies were undertaken to shed light on possible activation and deactivation mechanisms of Ziegler-Natta catalytic systems, as well as on the possible mechanisms for their reactivation by organohalides. We focused our efforts on Ti species attached to the (110) lateral cut of MgCl 2 . First, the possible activation of adsorbed TiCl 4 leading to an adsorbed Ti III species bearing a Ti-alkyl bond and a coordination vacancy, which is a species able to undergo chain-growth, was considered. According to our calculations formation of the first active species can be easily rationalized by cleavage of a Ti-Cl bond of coordinated TiCl 4 by AlEt 3 , followed by transalkylation promoted by another AlEt 3 molecule. Second, we investigated the possible reduction of polymerization active Ti III species leading to polymerization inactive Ti II species, and we found that a Ti-H bond, possibly formed after chain termination, is weaker than the Ti-Et (polymeryl) bond. Third, we investigated the mechanism of reactivation of Ti II species by organohalides, and it was concluded that reoxidation by Cl rich organohalides is thermodynamically more favored.

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In this article, polymerization of 1-hexene with FeCl 3-doped Mg(OET) 2 /TiCl 4 /electron donor (ED) catalytic system is presented. For this purpose, first a number of TiCl 4 catalysts supported on Mg(OEt) 2 and Fe-doped Mg(OEt) 2 supports were prepared with ethylbenzoate or dibutylphthalate as the internal EDs. After successive catalysts synthesis, they were employed in 1-hexene polymerization using cyclohexyl methyl dimethoxysilane as external ED as well as without it. The catalysts activity and molecular weight distribution (MWD) of poly 1-hexenes (PHs) were influenced strongly by both FeCl 3 doping and donor presence so that a remarkable increase in the catalyst activity was seen in doped catalysts. Deconvolution of MWD curves revealed that increase in the type of active centers by introducing FeCl 3 into the support should be responsible for the broadening of MWD of PHs. 13 CNMR analysis indicated that while isotacticity does not change considerably by Fe doping, EDs increase its amount as high as 8-21%. Second, the stereoselective behavior of active Ti species in doped and undoped catalysts was fully explored by molecular modeling using density functional theory (DFT) method. Finally, with the aid of rheological measurements, the processability of polymers were evaluated and then the gel permeation chromatography (GPC) results were approved through the values obtained from model fitting as well as changes in moduli crossover modulus.