Role of the (104) MgCl₂ Lateral Cut in Ziegler–Natta Catalysis: A Computational Investigation

Abstract

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.

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

“…Several experimental ,− and theoretical ,,− studies have been done to understand and develop a new robust Z–N catalyst system, in particular a donor catalyst system. It has been postulated from the third generation of catalysts that the addition of an electron donor in the Z–N system significantly influences the catalyst activity and stereoselectivity toward polypropylene. , After that Z–N researchers started to investigate different organic Lewis bases to design new and effective donor catalyst systems.…”

Insights into the Nature of Self‐Extinguishing External Donors for Ziegler‐Natta Catalysis: A Combined Experimental and DFT Study

“…Ziegler‐Natta (ZN) catalysis is one of the most important catalytic processes, which produces around 150 million tons of polyolefins/year, and has a billion dollar market [1] . Since its discovery in the 1950s by Karl Ziegler and Giulio Natta, for which they received the Nobel prize in 1963, [2,3] continuous efforts to improve the performance of the ZN systems, concerning their activity and the selectivity, have been undertaken, along with understanding at the molecular level, by employing various experimental [4–11] and computational tools [12–34] . The main components of the ZN system are (i) MgCl 2 as a catalyst support, (ii) TiCl 4 as precatalyst, (iii) triethylaluminum ( teal ) as an alkylating agent, and (iv) Lewis base donors (e. g. oxygen‐containing molecules and nitrogen‐containing polymers [35] ).…”

“…Donors are vital components of the ZN polymerization process that can enhance the stereo‐ and regioselectivity of the product by coordinating in the vicinity of the active titanium center [9,42,43,46] . It can influence the kinetics of the activation, insertion and termination steps in the polymerization reaction, and can also help the titanium to coordinate to the (104) MgCl 2 surface, which is otherwise unutilized [30,31,33] . It is interesting to note that tuning the structure of existing donors and developing new donors has always been challenging and a prominent area of research in ZN catalysis, because of their potential to produce polyolefins with desirable properties.…”

MgCl2‐supported Ziegler‐Natta catalysts: A DFT‐D ‘flexible‐cluster’ approach. TiCl4 and probe donor adducts

“…Modern DFT methods are able to describe the long‐range interactions which are an essential component of the bonding in such particles. This, together with tremendous progress in computer hardware, has made it possible to overcome the aforementioned limitations and constraints . In particular, while multilayered clusters are still problematic in the latter respect, monolayer clusters are well within reach.…”

“…This, together with tremendous progress in computer hardware, has made it possible to overcome the aforementioned limitations and constraints. [34] In particular, while multilayered clusters are still problematic in the latter respect, monolayer clusters are well within reach. In the present paper, we introduce the first DFT-D 'flexible-cluster' model of ZNC in which monolayer clusters of MgCl 2 with dimensions close to real coherent domains were simulated allowing for full structure relaxation.…”