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

Abstract

TiCl 4 /MgCl 2 catalysts are still the main industrial catalyst for isotactic polypropylene at present. However, the mechanism of isotactic polymerization of propylene has not been fully understood. DFT calculations revealed that the bare Ti active site was regioselective and nonstereoselective in the absence of an electron donor. The role of electron donor ethyl benzoate (EB), diethyl-2,3-diisobutylsuccinate (DiBS), cyclohexylmethyldimethoxysilane (CMDMS), and dicyclopentyldimethoxysilane (DCPDMS) on the active site was investigated. The presence of EB, DiBS, CMDMS, or DCPDMS around the Ti active site can promote the activity and retain the regioselectivity. It is worth noting that in the presence of EB and DCPDMS, the stereoselective behavior can be promoted with the advantage of 1 kcal/mol. The copresence of AlEt 2 Cl species and external donors can increase both the stereoselectivity and regioselectivity.

Understanding the Role of Sulfonyl Amine Donors in Propylene Polymerization Using MgCl2-Supported Ziegler–Natta Catalyst

“…A similar situation is also shown in the case of the chelatecoordinated internal donor diethyl-2,3-diisobutylsuccinate (sixth-generation). 34 Interestingly, in the case of chelatecoordinated BTFMSPA-o-DiPr and BTFMSnBA (Figure S4 in the Supporting Information), the stereoselectivity can be promoted, especially for BTFMSnBA with ΔG Stereo ‡ of 1.3 kcal/mol. The stereoselectivity can be effectively promoted by the bridge-coordinated donors, like BBSMA and BTFMSPAm-Cl (Figure 6).…”

“…31,32 In addition, the alkylation product AlR n Cl 3−n generated from AlR 3 could also be stably coordinated in the vicinity of the Ti active site, promoting the stereo-and regioselectivity of propylene insertion. 33,34 Despite the development from the third generation to the sixth generation, the role of electron donors and their relationship with other catalyst components remain elusive due to the high complexity of Ziegler−Natta catalysts. Fortunately, great efforts have been devoted to rationalizing the effect of electron donors on the catalytic system through experimental and theoretical methods.…”

“…Busico et al proposed a three-site model for Ziegler−Natta catalysts, where two bulky ligands L 1,2 (Cl or donor), one bulky ligand L 1 , and no bulky ligand coordinating to the adjacent unsaturated Mg 2+ around the Ti active site correspond to the highly isotactic, isotactic, and syndiotactic propagation, respectively. 62 To date, the effect of the traditional electron donors coadsorbed around the Ti active site on the propylene insertion has been investigated by Cavallo et al, 33,40,61 Terano et al, 59 Vanka et al, 63 Ziegler et al, 23 and Liu et al 34 In this work, the well-accepted stable Corradini site with a bulky ligand coadsorbed on the (110) surface was employed to investigate the effect of the new internal electron donor sulfonyl amine on propylene insertion. First, the adsorption of sulfonyl amine donors on the MgCl 2 (110) surface was studied in the case of the BTFMSPA-m-Cl donor.…”

“…More importantly, the suitable internal donor and external donor pair can enhance the stereoregularity of the polymer product. The internal donor is typically added during the catalyst preparation, e.g., ethyl benzoate (EB) (third generation), dialkyl phthalate (fourth generation), 1,3-diether (fifth generation), and dialkyl succinate (sixth generation). − The external donor is added during the olefin polymerization process in combination with the cocatalyst AlR 3 , e.g., silane, and alkoxysilane. − The appropriate internal donor and external donor pair can control the regularity of the polypropylene and greatly increase the yield of the isotactic polypropylene. , In addition, the alkylation product AlR n Cl 3– n generated from AlR 3 could also be stably coordinated in the vicinity of the Ti active site, promoting the stereo- and regioselectivity of propylene insertion. , …”

“…Busico et al proposed a three-site model for Ziegler–Natta catalysts, where two bulky ligands L 1,2 (Cl or donor), one bulky ligand L 1 , and no bulky ligand coordinating to the adjacent unsaturated Mg 2+ around the Ti active site correspond to the highly isotactic, isotactic, and syndiotactic propagation, respectively . To date, the effect of the traditional electron donors coadsorbed around the Ti active site on the propylene insertion has been investigated by Cavallo et al, ,, Terano et al, Vanka et al, Ziegler et al, and Liu et al…”