02013nas a2200169 4500008004100000022001400041245010400055210006900159260007100228300001400299490000700313520132800320100001901648700002701667700001701694856013201711 2014 eng d a0276-733300aDonor decomposition by lewis acids in Ziegler-Natta catalyst systems: a computational investigation0 aDonor decomposition by lewis acids in ZieglerNatta catalyst syst a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcSEP a4357-43670 v333 a

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.

1 aKumawat, Jugal1 aGupta, Virendra, Kumar1 aVanka, Kumar uhttps://library.ncl.res.in/content/donor-decomposition-lewis-acids-ziegler-natta-catalyst-systems-computational-investigation-001734nas a2200217 4500008004100000022001400041245011900055210006900174260007700243300001400320520087400334653002601208653003601234653002801270653001401298653001301312100001901325700002701344700001701371856012801388 2014 eng d a1434-194800aNature of the active site in ziegler-natta olefin polymerization catalysis systems - a computational investigation0 aNature of the active site in zieglernatta olefin polymerization  aBOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANYbWILEY-V C H VERLAG GMBHcOCT a5063-50763 a

Pull quantum chemical calculations with density functional theory (DET) show that a principal role of donors in Ziegler-Nana (ZN) oh-din polymerization catalysts is to coordinate to the metal center at the active sites on the MgCl2 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 chloride ligands at the titanium center (the conventional model for the active site) would lead to lower-molecular-weight riolymers. If an -OC2H5 group were present instead of a chloride ligand, the active site would much more effectively produce long chain polymers. Therefore, the current work provides important new insights into the nature of the ZN polymerization process.

10aAlkene polymerization10aDensity functional calculations10aheterogeneous catalysis10aInsertion10aPolymers1 aKumawat, Jugal1 aGupta, Virendra, Kumar1 aVanka, Kumar uhttps://library.ncl.res.in/content/nature-active-site-ziegler-natta-olefin-polymerization-catalysis-systems-computational-001843nas a2200229 4500008004100000022001400041245009900055210006900154260007500223300001400298490000600312520101500318653001501333653001301348653003601361653002201397653001301419100001901432700002701451700001701478856011801495 2016 eng d a1867-388000aEffect of donors on the activation mechanism in ziegler-natta catalysis: a computational study0 aEffect of donors on the activation mechanism in zieglernatta cat aPOSTFACH 101161, 69451 WEINHEIM, GERMANYbWILEY-V C H VERLAG GMBHcMAY a1809-18180 v83 a

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 (TiCl4)-Cl-IV catalyst converts into the active (TiCl2Et)-Cl-III 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.

10aAlkylation10aaluminum10aDensity functional calculations10asurface chemistry10atitanium1 aKumawat, Jugal1 aGupta, Virendra, Kumar1 aVanka, Kumar uhttps://library.ncl.res.in/content/effect-donors-activation-mechanism-ziegler-natta-catalysis-computational-study02657nas a2200169 4500008004100000022001400041245009800055210006900153260000800222300001200230490000800242520205600250100001902306700002702325700001702352856011802369 2018 eng d a1932-744700aRole of the (104) MgCl2 lateral cut in ziegler-natta catalysis: a computational investigation0 aRole of the 104 MgCl2 lateral cut in zieglernatta catalysis a co cJAN a285-2960 v1223 a

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 Z-N 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(CI)(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 (Delta X) was nearly the same for both the Cat-C and Cat-H eases, which shows that ethylene polymerization on the (104)MgCl2 surface is likely to be a ptoininent 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.

1 aKumawat, Jugal1 aGupta, Virendra, Kumar1 aVanka, Kumar uhttps://library.ncl.res.in/content/role-104-mgcl2-lateral-cut-ziegler-natta-catalysis-computational-investigation01978nas a2200169 4500008004100000022001400041245011700055210006900172260000800241300001400249490000800263520134800271100001501619700002701634700001701661856013001678 2023 eng d a1932-744700aPotential role of lewis acid-base adducts in enhancing stereoselectivity in ziegler-natta catalysts: a DFT study0 aPotential role of lewis acidbase adducts in enhancing stereosele cAPR a7220-72290 v1273 a

Ziegler-Natta (Z-N) systems have been well established as heterogeneous catalysts that produce isotactic polypropylene and polyethylene with great efficiency. Such systems benefit considerably from donors (Lewis bases), whose addition significantly improves the stereoselectivity of polymerization. There is a consensus that the primary role of the external donors is to coordinate at the vacant site created by the extraction of internal donors and thus maintain the stereoselectivity. However, the bite difference between internal donors such as phthalates or succinate derivatives and external donors such as alkoxysilanes raises the question of how external donors can effectively replace internal donors. In order to investigate this, we have chosen four external alkoxysilane donors: (1) diisopropyl dimethoxysilane, (2) dicyclopentyl dimethoxysilane, (3) disec-butyl dimethoxysilane, and (4) sec-butyl(methyl) dimethoxysilane. DFT studies reveal that the bite difference problem can be overcome by the favorable formation of adducts between the alkoxysilane external donors and AlEt2Cl in the Z-N systems. These adducts tend to coordinate in the vicinity of the active site. Furthermore, our findings demonstrate the potential of these Lewis acid-base adducts to enhance the stereoselectivity of Z-N catalysts significantly.

1 aRaj, Vipin1 aGupta, Virendra, Kumar1 aVanka, Kumar uhttps://library.ncl.res.in/content/potential-role-lewis-acid-base-adducts-enhancing-stereoselectivity-ziegler-natta-catalysts