Role of a Multidentate Carbonate Donor in MgCl₂-Supported Ziegler–Natta Olefin Polymerization Catalysis: An Experimental and Computational Approach

Abstract

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.

Mechanistic Study on Effect of Electron Donors in Propylene Polymerization Using the Ziegler–Natta Catalyst

“…In short, the proper electron donor coadsorbed on the TiCl 2 i Bu/MgCl 2 (110) surface can yield a moderately stereoselective site. This finding is in agreement with DFT calculations of Kumawat et al and Vanka et al , With regard to the copresence of AlEt 2 Cl species and the external donor, the stereoselectivity can be promoted by the increased steric hindrance around the Ti active site.…”

Monitoring the Kinetics of Internal Donor Clean-up from Ziegler–Natta Catalytic Surfaces: An Integrated Experimental and Computational Study

“…For the present study, a monolayered model cluster with 27 MgCl 2 units was built so as to feature predominant MgCl 2 (110)-like lateral terminations (short notation, CLU-27–110 ); a molecule of DBP was chemisorbed in chelating mode (Figures S4 and S5 (Supporting Information)). , In the first place, the thermodynamic parameters of DBP adsorption/desorption were estimated. The calculated values of adsorption enthalpy and free energy (Δ H ads ≈ −50 kcal mol –1 , Δ G ads ≈ −35 kcal mol –1 at 298 K; Table , entry 1) agree nicely with previous studies. , The process of DBP desorption with formation of a DBP·(AlEt 3 ) 2 adduct was found to be strongly endergonic; as a matter of fact, the decreases of enthalpy and free energy associated with the formation of the adduct (Table , entry 2, and Table S6 (Supporting Information)) are not sufficient to compensate the increases of the same parameters due to DBP desorption (Table , entry 3). These results endorse the experimental conclusion that DBP reduction occurs on MgCl 2 surface.…”

“…The calculated values of adsorption enthalpy and free energy (ΔH ads ≈ −50 kcal mol −1 , ΔG ads ≈ −35 kcal mol −1 at 298 K; Table 2, entry 1) agree nicely with previous studies. 25,32 The process of DBP desorption with formation of a DBP•(AlEt 3 ) 2 adduct was found to be strongly endergonic; as a matter of fact, the decreases of 1) Next, we modeled the first Et transfer from AlEt 3 to chemisorbed DBP (Scheme 1b). A six-membered TS (Scheme 2a) and a four-membered TS (Scheme 2c) were evaluated; 41,45 the two optimized TS structures are shown comparatively in Figure 3.…”

Cat-CrNP as new material with catalytic properties for 2-chloro-2-propen-1-ol and ethylene oligomerizations

“…Since the 1990s, when post-metallocene catalysts were invented, research into polymerization catalysts and material and polymer products became more popular and carried out with greater intensity 1 , 2 . Nowadays, new materials are sought to act as catalysts for olefin polymerization and oligomerization 3 – 5 .…”