Full quantum chemical calculations with density functional theory (DFT) show that a principal role of donors in ZieglerNatta (ZN) olefin polymerization catalysts is to coordinate to the metal center at the active sites on the MgCl 2 surface. Thereby, the behavior of the catalyst is modulated to favor insertion over termination and, thus, polymerization occurs. This is shown to be true for a range of different donors. The calculations indicate that active sites that feature anionic

MgCl2 supported Ziegler–Natta (Z–N) catalyst have emerged as a most exciting chemical process for polyolefin technology, which is responsible for production of ~150 million ton polyolefin (polyethylene and polypropylene) per...

The development of new donors (Lewis bases, usually containing oxygen atoms) is one of the chief areas of research in Ziegler–Natta (ZN) olefin polymerization systems. The addition of such donors has led to improvement in the activity and selectivity of ZN systems. However, in order for the donor to be effective, it has to be chemically stable and resistant to decomposition by Lewis acidic species such as AlEt3. Discussed in the current work is the chemical stability of different ester donors, including aromatic benzoate donors and 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 different pathways upon interaction with species such as the AlEt3 dimer: Al2Et6. Moreover, the studies show that the active, supported titanium catalyst species can cause donor decomposition and, in fact, is likely to be the greater threat to donor decomposition than Al2Et6. This explains why the addition of excess donors can lead to the poisoning of the active site in ZN systems. We have also computationally investigated means of improving the silyl ester donors in order to make them more robust and resilient to donor decomposition by Al2Et6 and the supported active titanium species.

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.

A new multidentate carbonate (3,3,3′,3′-tetramethyl-2,2′,3,3′-tetrahydro-1,1′-spirobiindane-5,5′,6,6′-tetracarbonate) is studied as a potential internal electron donor for Ziegler−Natta (Z−N) catalysts. The non-phthalate nature of the multidenate carbonate donor has an advantage in comparison to hazardous phthalate donors. The multidentate carbonate donor coordination to the MgCl 2 surface is investigated through mono-, bi-, tri-, and tetradentate modes using density functional theory. These calculations indicate that the tridentate donor coordination is thermodynamically more favorable with respect to the mono-, bi-, and tetradentate ones. Ethylene polymerization with the multidentate carbonate as the internal electron donor is studied, and medium-to high-molecular-weight polyethylene is observed, which is confirmed by intrinsic viscosity (IV) and melt flow index analysis. The experimental findings are validated by quantum chemical calculations, which suggest that the multi(bi)dentate (multicarbonate donor with bidentate coordination) active site leads to high-molecular-weight polymers, whereas the multi(tri)dentate and multi(tetra)dentate donor active sites only form oligomers owing to less space on the titanium center for the incoming monomer. For a comparative study, phthalate, diether, and succinate donors are also employed for ethylene polymerization. Furthermore, the regio-and stereoselective behavior of a propylene monomer on Ti−alkyl bonds (alkyl = −Et and -isobutyl) is investigated for all donor cases, and it is found that the multidentate carbonate is equally effective as other donors. Therefore, the current multidentate carbonate donor catalyst study sheds light on the nature of different adsorption modes of donors on the MgCl 2 support and how this new multidentate carbonate donor influences the Z−N olefin polymerization process.

Density functional theory has been used to study single to multiple site behavior of metallocene catalysts for olefin polymerization using (Cp Pr ) 2 Hf(R) 2 and (Cp Pr ) 2 Zr(R) 2 (here, R = Me and n-butyl group) and boron activators B(C 6 F 5 ) 3 and [CPh 3 ] + [B(C 6 F 5 ) 4 ] − . Detailed pathways were investigated for two steps: (i) catalyst activation and (ii) ethylene and 1-hexene polymerization. For the catalyst activation step, the C−H activation of Cp-substituents (here, the n-propyl group) has also been studied, which leads to another active site named "metal cyclic active site" in comparison to the conventional active site. Among these sites, the formation of a metal cyclic active site is slower with respect to the conventional active site. Additionally, two different routes have been explored for the catalyst activation, depending on the nature of activators, and observed that [CPh 3 ] + [B(C 6 F 5 ) 4 ] − is a better activator with respect to B(C 6 F 5 ) 3 . Moreover, complete insertion (primary and secondary) and termination (chain transfer to monomer and β-H elimination) steps have also been studied for both the active sites. These results suggest that the metal cyclic active site can also produce the ethylene and 1-hexene polymer, which defines the multiple site behavior of metallocene catalysts, which explains the broadening of molecular weight distribution of linear low-density polyethylene-produced metallocene catalysts. Along with hafnocene and zirconocene, the toluene-solvated hafnocene catalyst system has also been investigated for catalyst activation and ethylene polymerization for comparison study. These results indicate that the toluene-solvated hafnocene catalyst system is energetically more facile in comparison to other catalysts. Furthermore, the effect of solvents as well as dispersion interaction on catalyst activation steps has been studied for the (Cp Pr ) 2 M(n-butyl) 2 (M = Hf and Zr) catalyst systems and observed that the dispersion interaction played an important role in the catalyst activation process. In addition to this, the regio-and stereoselective behavior of 1-hexene monomer for the (Cp Pr ) 2 Hf(Me) 2 catalyst has been investigated, and it was found that the metal cyclic active site improves the stereoselective nature of the hafnocene catalyst. Therefore, the current chemical calculations provide insights into the nature of active sites in metallocene catalysts for olefin polymerization.

We report a combined multivariate linear regression (MLR) and density functional theory (DFT) approach for predicting the comonomer incorporation rate in the copolymerization of ethene with 1olefins. The MLR model was trained to correlate the incorporation rate of a set of 19 experimental group 4 catalysts to steric and electronic features of the dichloride catalyst precursors. Although the assembled experimental data were produced in different laboratories and both propene and 1hexene copolymerization results were considered, the trained MLR model results in a R 2 value of 0.82 and a leave-one-out Q 2 value of 0.72. The trained model was validated against a validation set comprising 3 catalysts from the literature and not included in the training set plus one catalyst synthesized by us. Except for one literature catalyst, data in the validation set were predicted with reasonable accuracy. Additionally, a catalyst synthesized by us, for which the MLR model predicted a comonomer incorporation of 4.0%, resulted in a 1-hexene experimental incorporation of 4.5−5%. The trained MLR model was used to predict the comonomer incorporation rate of 10 related zirconocenes having structural features similar to the 19 systems in the training set. We further explored the impact of the precatalyst structure on the comonomer incorporation rate by analyzing a set of 15 zirconocenes having steric and electronic features different from those in the training set. These predictions were validated by DFT calculations.

Density functional theory (DFT) has been used for the study of ethylene polymerization in the Ziegler–Natta (ZN) olefin polymerization system for eight different alkoxy group containing titanium catalysts (Cat-A–H), Ti­(III)­Et­(OR)­(OR′) (where R = −CH3, – Et, −tert-butyl, −cyclohexane, R′ = −CH3, −Et, −tert-butyl, −cyclohexane). What is of significance is that the catalysts studied were all considered to be tethered to the (104) MgCl2 surface, which has traditionally been considered a “dormant” surface in ZN catalysis systems, in contrast to the “more active” (110) MgCl2 surface. Our calculations indicate that the binding of all the catalysts to the (104) surface is favorable, even after taking entropic effects into account. For purposes of comparison, ethylene polymerization has been investigated for the Cat-C (TiEt­(OEt)2) and the Cat-H (TiEt­(Cl)­(OC4H8Cl)) (OC4H8Cl = the chlorobutoxy group) cases, for both the (i) (110) and the (ii) (104) MgCl2 surfaces. It has been seen that for both (i) and (ii) the energy gap between insertion and the termination barriers (ΔX) was nearly the same for both the Cat-C and Cat-H cases, which shows that ethylene polymerization on the (104) MgCl2 surface is likely to be a prominent occurrence in Z–N catalysis, when alkoxy groups are bound to the titanium center. Additionally, for the Cat-C and the Cat-H cases, the regio- and stereoselective behavior of the propylene monomer on the titanium species present on the (110) and the (104) MgCl2 surfaces has also been investigated, and the results indicate that the (104) MgCl2 surface is only slightly less effective than the (110). However, the calculations also indicate that for Cat-H the (104) MgCl2 surface significantly improves the molecular weight of polypropylene in comparison to the (110) surface, further showcasing how the (104) surface (ignored until date) might be a major player in ZN catalysis. Given that a major portion of the MgCl2 support is made up of (104) lateral cuts, the current findings are of considerable relevance.