*Article* **The Effect of Titanium Tetra-Butoxide Catalyst on the Olefin Polymerization**

**Mohammed S. Alsuhybani and Eid M. Alosime \***

King Abdulaziz City for Science and Technology (KACST), P.O. Box 6086, Riyadh 11442, Saudi Arabia; sohybani@kacst.edu.sa

**\*** Correspondence: alosimi@kacst.edu.sa

**Abstract:** The purpose of this study was to assess the ability of titanium Ti(IV) alkyloxy compounds supported by organic polymer polyvinyl chloride (PVC) to polymerize ethylene by feeding triethylaluminium (TEA) as a cocatalyst. Additionally, the impacts of the molar ratio of [Al]/[Ti] on the catalytic activities in ethylene's polymerization and of the comonomer through utilization of diverse quantities of comonomers on a similar or identical activity were studied. The optimal molar ratio of [Al]/[Ti] was 773:1, and the prepared catalyst had an initial activity of up to 2.3 kg PE/mol Ti. h. when the copolymer was incorporated with 64 mmol of 1-octene. The average molecular weight (*M*w) of the copolymer produced with the catalysts was between 97 kg/mol and 326 kg/mol. A significant decrease in the *M*w was observed, and PDI broadened with increasing concentration of 1-hexene because of the comonomer's stronger chain transfer capacity. The quick deactivation of titanium butoxide Ti(OBu)4 on the polymers was found to be associated with increasing oxidation when supported by the catalyst. The presence of Ti(III) after reduction with the aluminum alkyls cleaves the carbon-chlorine bonds of the polymer, producing an inactive polymeric Ti(IV) complex. The results show that synergistic effects play an important role in enhancing the observed rate of reaction, as illustrated by evidence from scanning electron microscopy (SEM). The diffusion of cocatalysts within catalytic precursor particles may also explain the progression of cobweb structures in the polymer particles.

**Keywords:** polyethylene; olefin polymerization; Ziegler–Natta; polyvinyl chloride

#### **1. Introduction**

Ziegler-Natta (ZN) catalysts are the most commonly used catalysts in the olefin polymerization industry [1]. They are mainly composed of transition metal compounds, such as titanium, chromium, and vanadium precursors [2], and they are considered the best option for olefin polymerization industries because of their high productivity and good morphology control [3]. They undergo activation through the use of either an activator or a cocatalyst that activates inactive sites [4]. The most commonly used cocatalysts are alkylaluminium based, such as triethylaluminium (TEA) and tri-octyl aluminum [5,6].

MgCl2 in combination with either TiCl4 or TiCl3 enhances the effectiveness of ZN catalysts and TEA cocatalysts [7,8]. In the synthesis of a novel chromium SiO2/MgObased ZN catalyst using water-soluble magnesium sources, the Cr-Ti catalysts have been reported to increase the polymerization activity and can generate polyethylene with a favorable hydrogen response [9]. Kinetic investigations of ethylene polymerization have demonstrated that two types of active sites, TiCl4 and Cp2ZrCl2, are formed when TiCl4 and zirconocene (Cp2ZrCl2) catalysts are anchored with a MgCl2(THF)2 support and then activated using TEA and methylaluminoxane [10]. Furthermore, silicon dioxide (SiO2) has also been utilized as a support [11].

A MgCl2/SiO2 bisupport utilizes magnesium acetate as a source of Mg. When MgCl2/SiO2 reacts with TiCl4 and VOCl3 under different reaction sequences, ZN hybrid titanium/vanadium catalysts are formed [12]. The effectiveness of the Ti/V hybrid

**Citation:** Alsuhybani, M.S.; Alosime, E.M. The Effect of Titanium Tetra-Butoxide Catalyst on the Olefin Polymerization. *Polymers* **2021**, *13*, 2109. https://doi.org/10.3390/ polym13132109

Academic Editor: Edina Rusen

Received: 16 June 2021 Accepted: 25 June 2021 Published: 26 June 2021

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catalysts lies between that of the MgTi/Si and MgV/Si catalysts. However, the Ti/V hybrid catalysts, which result from a coreaction with TiCl4 and VOCl3, show increased activity compared with the Ti/V hybrid catalysts prepared using a two-step mechanism [13].

The polymerization rate is influenced by factors such as the concentration of the active center, the propagation rate constant, and the monomer concentration [14]. The concentration of the monomer changes gradually as one moves from the surface toward the core of the polymer/catalyst particles [15,16]. The concentration of the monomer is assumed to remain even across the entire polymer medium, whereas the propagation rate constant highly depends on the stereospecificity of the active centers [17]. The increased concentration of the active center promotes the activity of the ZN catalysts [18]. In addition, an appropriate amount of diethylaluminium chloride is added to the ZN catalyst system. Here, alongside TEA as the cocatalyst, the catalytic activity increases [19].

The functional groups within polymer structures play a crucial role in promoting the formation of either chemical bonds or interactions between the polymers and catalysts [20]. However, polymers such as atactic poly(propylene), natural rubber, and polyvinyl chloride are characterized by low-surface free energies and a lack of functional grouping. Therefore, they cannot interact with ZN catalysts unless functional groups are introduced [21]. Catalytic systems containing chlorine either as part of the support or as a cocatalyst exhibit enhanced activity; therefore, to allow for the study of their activities, PP, NR, and PVC are chlorinated before being subjected to the heterogenization of the ZN catalyst [22].

Recently, it has been discovered that the use of Ti(IV) alkoxide complexes—with 1,2 and 1,4-diolate ligands activated by a binary activator {Bu2Mg + Et2AlCl} and as a catalyst during the polymerization process of ethylene—results in the formation of an ultrahigh molecular weight polyethylene (UHMWPE) [23]. Ti(IV) complexes with diolate ligands are also very efficient in the copolymerization of ethylene and α-olefins. However, the effectiveness of the various diolate complexes differs based on the size of the chelate ring and the amount of aluminum chloride used [23].

In the current paper, we present our experiments, which are aimed at further understanding ZN catalysts and the processes for olefin polymerization. The titanium tetrabutoxide Ti(OBu)4 compound was used as a compound-containing oxygen to determine the impact on the TiCl4 catalyst, which was supported using PVC polymeric material. The latter was treated by a Grignard compound, and TEA (Al(C2H5)3) was used as a cocatalyst. The utilization of a PVC-based polymeric support in preparing the catalyst provided important benefits compared with contemporary methods that use polymerization catalysts supported by magnesium chloride (MgCl2) and SiO2. Moreover, the PVC-based polymeric supports (or particles) for preparing the catalysts have shortened the dehydration duration and steps, allowing for lower temperatures compared with the polymerization catalysts supported by MgCl2 and SiO2. Therefore, PVC-based polymeric supports (or particles) are more suitable for synthesizing catalysts because they simplify the synthesis process, leading to a significant reduction in the cost of preparing catalysts. Additionally, the cost of PVC-based support tends to be considerably lower compared with polymerization catalysts that are supported by MgCl2 and SiO2. Similarly, the catalyst substantially utilizes the lowest levels of catalyst precursors in preparing the catalyst compared with the polymerization catalysts supported by MgCl2 and SiO2. The catalytic activities of Ti(OBu)4 catalysts, for both ethylene homopolymerization and its copolymerization, ethylene, and 1-octene and ethylene and 1-hexene, were assessed.

#### **2. Experiment**

#### *2.1. Materials*

Ethylene gas was supplied from Abdullah Hashem Co., Saudi Arabia, with a purity of 99.95%. Here, *n*-hexane served as a polymerization medium in the heterogenous phase and was purchased from BDH® with a purity of 99%. In addition, 1-octane was purchased from Ried Dehean, and 1-hexene was obtained from Advanced Engineering, UK, and dried over 5 Å molecular sieves before use. Butylmagnesium chloride (BuMgCl) was purchased

from Aldrich Chemical (2 M in THF). Titanium(IV) butoxide (Ti(OBu)4) with 100% purity was purchased from Akzo Chemie America. PVC spheres with an average particle size of 50 μm were used (supplied by SABIC, Riyadh, Saudi Arabia). All support and catalyst synthesis and characterizations were performed under inert gas.
