Ti-based Ziegler-Natta Catalyst Research Articles

Temperature Dependence of the Kinetic Parameters of the Titanium–Magnesium Catalyzed Propylene Polymerization

This paper provides a study of the liquid-phase polypropylene polymerization on a heterogeneous titanium-magnesium Ziegler-Natta-type catalyst. A kinetic model was developed that included the activation of potential active centers, chain growth, transferring the chains to hydrogen and monomer, and the deactivation of active centers. The model was created to predict the polymerization rate, polymer yield, and average molecular weights of polymer chains where the polymerization temperature changes from 40 to 90 °C. In developing polycentric kinetic models, there is a difficulty associated with evaluating the kinetic constants of the rates of elementary reactions/stages in polymerization. Each heterogeneous titanium-magnesium catalyst (TMC), including a co-catalyst, as well as an internal and an external electron donor, has its own set of kinetic parameters. Therefore, its kinetic parameters must be defined for each new catalyst. The presented algorithm for identifying the kinetic constants of rates starts with a kinetic model that considers one type of active centers. At the second stage, a deconvolutional analysis is used for the molecular weight distribution (MWD) of the gel permeation chromatography (GPC) data of the polypropylene samples and the most probable distribution of Flory chain lengths is found for each type of active centers. At the third stage, the single-center model is transformed into a polycentric kinetic model. For the catalyst system, five types of active centers were identified, together with a mass fraction and a number-average molecular weight for each active center type of the catalyst, which is consistent with the published results for similar Ti-based Ziegler-Natta catalysts.

Gas-phase polymerization of ethylene over Ti-based Ziegler–Natta catalysts prepared from different magnesium sources

This study focuses on gas-phase polymerization of ethylene using the titanium-based Ziegler–Natta catalysts prepared from different magnesium sources including MgCl2 (Cat A), magnesium powder (Cat B), and Mg(OEt)2 (Cat C). During polymerization, different cocatalysts were also used. It was found that Cat C with triethylaluminum as a cocatalyst exhibited the highest activity. This was likely attributed to optimal distribution of active sites on the catalyst surface. It can be observed by increased temperature in the reactor due to highly exothermic reaction during polymerization. By the way, the morphologies of the polymer obtained from this catalyst were spherical, which is more preferable. Besides the catalytic activity, crystallinity and morphology were also affected by the different magnesium sources used to prepare the catalysts.

Preparation of PP/2D-Nanosheet Composites Using MoS2/MgCl2- and BN/MgCl2-Bisupported Ziegler–Natta Catalysts

Polypropylene/molybdenum disulfied (PP/MoS2) and Polypropylene/hexagonal boron nitride (PP/hBN) nanocomposites with varying concentration (0–6 wt %) were fabricated via in situ polymerization using two-dimensional (2D)-nanosheet/MgCl2-supported Ti-based Ziegler–Natta catalysts, which was prepared through a novel coagglomeration method. For catalyst preparation and interfacial interaction, MoS2 and hBN were modified with octadecylamine (ODA) and octyltriethoxysilane (OTES), respectively. Compared with those of pristine PP, thermal stability of composites was 70 °C higher and also tensile strength and Young’s modulus of the composites were up to 35% and 60% higher (even at small filler contents), respectively. The alkyl-modified 2D nanofillers were characterized by strong interfacial interactions between the nanofiller and the polymer matrix. The coagglomeration method employed in this work allows easy introduction and content manipulation of various 2D-nanosheets for the preparation of 2D-nanosheet/MgCl2-supported Ti-based Ziegler–Natta catalysts.

Facile Investigation of Ti3+ State in Ti-based Ziegler-Natta Catalyst with A Combination of Cocatalysts Using Electron Spin Resonance (ESR)

This study aims to investigate the influences of a combination of cocatalysts including triethylaluminum (TEA) and tri-n-octylaluminum (TnOA) for activation of a commercial Ti-based Ziegler-Natta catalyst during ethylene polymerization and ethylene/1-hexene copolymerization on the change in Ti3+ during polymerization. Thus, electron spin resonance (ESR) technique was performed to monitor the change in Ti3+ depending on the catalyst activation by a single and combination of cocatalyst. It revealed that the amount of Ti3+ played a crucial role on both ethylene polymerization and ethylene/1-hexene copolymerization. For ethylene polymerization, the activation with TEA apparently resulted in the highest catalytic activity. The activation with TEA+TnOA combination exhibited a moderate activity, whereas TnOA activation gave the lowest activity. In case of ethylene/1-hexene copolymerization, it revealed that the presence of 1-hexene decreased activity. The effect of different cocatalysts tended to be similar to the one in the absence of 1-hexene. The decrease of temperature from 80 to 70 °C in ethylene/1-hexene copolymerization tended to lower catalytic activity for TnOA and TEA+TnOA, whereas only slight effect was observed for TEA system. The effect of different cocatalyst activation on the change of Ti3+ state of catalyst was elucidated by ESR measurement. It appeared that the activation of catalyst with TEA+TnOA combination essentially inhibited the reduction of Ti3+ to Ti2+ leading to lower activity. Furthermore, the polymer properties such as morphology and crystallinity can be altered by different cocatalysts. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

47,49Ti solid-state NMR and DFT study of Ziegler-Natta catalyst: Adsorption of TiCl4 molecule onto the surface of MgCl2

In Ti-based Ziegler-Natta catalysts (ZNCs), disagreements exist concerning which lateral surface of the MgCl2 support adsorbs Ti species so as to be an active site for the catalysis of polymerization. In the present paper, we investigated the local structure of TiCl4 adsorbed onto the surface of MgCl2 by 47,49Ti solid-state nuclear magnetic resonance (NMR) spectra at 21.8 T along with density functional theory (DFT) calculations. The magic-angle-spinning NMR spectrum of the TiCl4/MgCl2 adduct sample prepared by 20 h of milling, which exhibited broadened and shifted peaks compared to that of the sample without milling, was simulated by a Czjzek model considering the distribution of quadrupole interaction parameters. The electric field gradient and chemical shielding tensors of 49Ti were obtained via DFT calculations for model molecules of TiCl4, 2TiCl4, and Ti2Cl8 adsorbed onto the (110), (104), and (104)-step defect surfaces of MgCl2. By comparing the obtained NMR parameters, the 47,49Ti NMR spectrum of the milled sample was assigned to TiCl4 adsorbed onto the (104) surface of MgCl2, which may not be a principal component of adsorption.

The mechanical properties of polyethylene/graphene nanocomposites by in-situ synthesis

Using graphene modified polyethylene can make up many shortcomings for polyethylene such as insufficient toughness, poor creep resistance and so on. In our research, graphene oxide was prepared by Hummers method assisted with ultrasonic treatment, then di-n-butylmagnesium was used to react with graphene oxide to generate an intermediate, which was adopted to prepare graphene-supported Ti-based Ziegler-Natta catalyst. Thereafter, the polyethylene/graphene nanocomposites were synthesized by this catalyst. It was found that heterogeneous nucleation effect of graphene could enhance polyethylene crystallization, increase lamella thickness and crystallinity of nanocomposites as well as crystallization temperature. Graphene can capture the free radicals generated when HDPE decomposed, which increased the thermal stability of composites. At the same time, the dielectric constant and conductivity of composites increased with the increase of graphene content, which reflected the good interfacial polarization effect in materials.

Graphene/carbon nanotubes-supported Ziegler-Natta catalysts for in situ synthesis of mechanically strong, thermally and electrically conductive trans-polyisoprene nanocomposite

Facile ball milling process is introduced here to prepare an efficient rGO/CNT/MgCl2 supported Ti-based Ziegler-Natta catalyst, for in situ polymerization of isoprene and simultaneous production of rGO/CNT based trans-polyisoprene (TPI) hybrid nanocomposite (having 98% of trans-1,4 structure). Effect of rGO/CNT on the morphological and crystalline properties of the catalyst, along with its efficacy towards the polymerization has been thoroughly investigated by SEM, XRD, FTIR, 1H-NMR, 13C-NMR, etc. Surprisingly, β-crystallinity of TPI nanocomposite increases with increasing rGO/CNT content. Because of increasing crystallinity and presence of homogeneously dispersed rGO/CNT filler, TPI nanocomposite (containing only 2 wt% rGO/CNT) shows improved mechanical property (e.g., increase of 110% modulus at 300% strain), 65% increased thermal conductivity and 109 time increased electrical conductivity.

Preparation of Octadecylamine-Graphene/MgCl₂-Supported Ziegler-Natta Catalyst and Its Application in Ethylene Polymerization.

A facile coagglomeration method for preparing a long alkyl chain modified graphene oxide (MGO)/MgCl2-supported Ti-based Ziegler-Natta catalyst was reported. The effects of MGO on the catalyst morphology and activity for ethylene polymerization were examined. The resultant polyethylene (PE)/MGO nanocomposites exhibited a layered morphology, with the MGO fillers being well dispersed and exhibiting strong interfacial adhesion to the PE matrix. The thermal stability and mechanical properties of the PE were significantly enhanced with the introduction of a small amount of the MGO filler. Thus, this work provides a facile approach to the production of high-performance PE.

Preparation of graphene/MgCl2-supported Ti-based Ziegler-Natta catalysts by the coagglomeration method and their application in ethylene polymerization

We report a facile coagglomeration method for preparing graphene (G)/MgCl2-supported Ti-based Ziegler-Natta catalysts. The effects of graphene feed ratio on catalyst morphology and ethylene polymerization behavior were examined. The synthesized catalyst exhibited very high activity for ethylene polymerization. The resultant polyethylene (PE)/G nanocomposites showed a layered morphology, and the graphene fillers were well dispersed in the PE matrix. In addition, the thermal stability and mechanical properties of PE were significantly enhanced with the introduction of a very small amount of G fillers (0.05 wt%). This work provides a facile approach to the production of high-performance PE.

Preparation and properties of PE/MoS2 nanocomposites with an exfoliated-MoS2/MgCl2-supported Ziegler-Natta catalyst via an in situ polymerization

Here, we report the first example of preparation of polyethylene (PE)/exfoliated-MoS2 nanocomposites through in-situ Ziegler-Natta polymerization. The exfoliated-MoS2/MgCl2-supported Ti-based Ziegler–Natta catalyst was synthesized via a facile coagglomeration method. The effects of MoS2 on the catalyst morphology and the ethylene polymerization behavior were examined. The resultant PE/MoS2 nanocomposites had a flake shape morphology, and the MoS2 fillers were well dispersed throughout the entire PE matrix. In addition, the thermal stability and mechanical properties of the PE base material were significantly enhanced by the introduction of a very small amount of the MoS2 filler (0.08wt%). Therefore, this work provides a facile method to produce of high-performance PE.

Fabrication of polyethylene/graphene nanocomposites through in situ polymerization with a spherical graphene/MgCl2-supported Ziegler-Natta catalyst

In this study, a spherical grapheme (G)/MgCl2-supported Ti-based Ziegler-Natta catalyst was prepared by a facile spray-coagglomeration method. The effects of graphene on catalyst morphology, ethylene polymerization behavior, and polymer properties were investigated. The resultant product was spherical, and the G was well dispersed in the whole polyethylene (PE) matrix. In addition, the thermal stability and mechanical properties of PE were significantly enhanced with the introduction of a very small amount of G (0.09 wt%) due to good dispersion of the graphene fillers in the PE matrix. Thus, this work provides a facile approach for the production of high-performance PE.

Accelerating the Research Approach to Ziegler–Natta Catalysts

Despite 60 years of history and a stunning success, Ti-based Ziegler–Natta catalysts for the production of isotactic polypropylene remain black-box systems, and progress still relies on trial and error. This represents a limitation in a moment when the most widely used industrial systems, containing phthalates as selective modifiers, need to be replaced because of a recent REACH ban. In view of the great complexity of the chemical and physical variables and the heavy nonlinearity of their effects, a high-/medium-throughput approach to this catalysis is highly desirable; herein we introduce an integrated medium-throughput workflow spanning from propene polymerization to polypropylene microstructural characterization and combining a 102-fold throughput intensification with quality standards equal or higher than conventional methods.

Effects of GO oxidation degree on GO/BuMgCl-supported Ti-based Ziegler–Natta catalyst performance and nanocomposite properties

The effects of GO oxidation degree on catalyst performance were studied. The resultant PE/rGO product exhibited significant increase in mechanical properties of commercial PE due to the well dispersion and good interface adhesion with the PE matrix.

PE/Clay Nanocomposite with Bimodal Molecular Weight Distribution Produced Via In-Situ Polymerization

A Ti-based Ziegler–Natta catalyst supported on the clay was used for producing the polyethylene/clay nanocomposites through in situ polymerization. This catalyst showed high activity in the ethylene polymerization. The two-step polymerization approach, i.e. in the presence and absence of hydrogen, was laid out to broaden the molecular weight distribution of the polyethylene/clay nanocomposite. The molecular weights and molecular weight distribution of the nanocomposites were characterized by the gel permeation chromatography. It was found that the molecular weight distribution was remarkably widened towards bimodal distribution by using the above mentioned approach. The thermal properties of the produced nanocomposites were studied by differential scanning calorimetry and thermal gravimetric analysis. The microstructure of the resulting bimodal polyethylene/clay nanocomposite was investigated by X-ray diffraction and transmission electron microscopy. The thermal gravimetric analysis indicated an improved thermal stability of the produced nanocomposites. In addition, the studies proved the nanocomposite formation with the exfoliated structure of the clay in the polyethylene matrix.

Wear behavior of in situ polymerized carbon nanotube/ultra high molecular weight polyethylene composites

A carbon nanotube (CNT)/ultra high molecular weight polyethylene (UHMWPE) composite has been prepared through in situ polymerization of ethylene using Ti-based Ziegler-Natta catalysts fixed on the surface of CNT. The in situ polymerization of ethylene produced CNTs regularly encapsulated with UHMWPE, which showed very uniform dispersion of CNTs in the UHMWPE matrix after direct molding. In tensile and ring-on-block wear tests, the in situ polymerized composites showed mechanical and wear properties superior to mechanically blended composites. In particular, the polymerized composite displayed a remarkable suppression of abrasive wear, which was the wear mechanism observed in unfilled UHMWPE and mechanically blended composites; the in situ polymerized composite containing about 10 wt% of CNT had an approximately 2.5 times lower wear rate than unfilled UHMWPE. Moreover, the polymerized composite showed higher thermal conductivity with CNT content when compared to the blended composites, which suggests an easier transfer of heat generated during a severe wear operation.

Active centers in Ziegler–Natta catalysts: Formation kinetics and structure

The article presents experimental data on the formation rates of active centers in polymerization reactions of ethylene with solid Ti-based Ziegler–Natta catalysts (γ and δ forms of TiCl3, TiCl2) and five types of supported catalysts, TiCl4/MgCl2/SiO2, TiCl3/MgCl2/SiO2 and TiCl4/MgCl2/diisobutyl phthalate. Effects of the following factors on the center formation are discussed: reaction temperature, monomer concentration, the amount of cocatalyst, the initial valence state of Ti atoms in the catalyst, pre-reactions of catalysts with cocatalysts, the presence of molecular hydrogen, effects of 1-alkenes in ethylene polymerization reactions. A combination of the results produces the basis for the formation mechanism of active centers in Ziegler–Natta catalysts, which involves reduction of numerous Ti species on the catalyst surface to IITi and oxidation addition of alkenes to IITi with the generation of IVTi-based polymerization centers.

The effects of partial replacement of TiCl4 by Ti(OR)4 on the performance of MgCl2-supported Ziegler–Natta catalysts

In a Ti-based Ziegler–Natta catalyst with in situ generated MgCl2, the titanium tetrachloride (TiCl4) was partially replaced by titanium tetra-alkoxide (Ti(OR4)), where R was either ethyl or n-butyl, and the effect of the addition order of the titanium compound was evaluated. For comparison, two other catalysts were synthesized: (1) one had the same amount of Ti, exclusively from TiCl4; (2) the other is employed in industrial processes and was used as the reference. Ti3+ comprised 85% of the total amount of titanium added during the catalyst synthesis. The amount of soluble Ti in the supernatant phase was at most 0.002molL−1, indicating that the added Ti reacted with the support. In general, Ziegler–Natta catalysts demand a significant amount of raw materials, while these catalysts require a lower amount of titanium compounds and save a significant amount of solvent in particular during the synthesis (approximately 80%). The preparation time of the catalysts was also reduced. The performance of these catalysts during ethylene polymerization suggests that adding Ti(OR)4 created a catalyst with a similar activity and ability to form high-density polyethylene as the reference catalyst.

Effects of Switching Frequency of a Periodic Switching Polymerization Process on the Microstructures of Ethylene–Propylene Copolymers in Polypropylene/Poly(ethylene-co-propylene) in-Reactor Alloys

This work deals with the effects of the switching frequency of a periodic switching polymerization process (PSPP) with a Ti-based Ziegler–Natta catalyst on the microstructures of ethylene–propylene...

Effect of γ-Ray irradiation on surface oxidation of ultra high molecular weight polyethylene/zirconia composite prepared byin situ ziegler-natta polymerization

Novel ultra-high molecular weight polyethylene (UHMWPE)/zirconia composites were previously prepared by thein situ polymerization of ethylene using a Ti-based Ziegler-Natta catalyst supported on to the surface of zirconia, as a bearing material for artificial joints. Tribological tests revealed that a uniform dispersion of zirconia in UHMWPE markedly increased the wear resistance. The effects of zirconia content on the oxidation behavior of the γ-ray-treated UHMWPE/zirconia composite surfaces were examined. The oxidation index that estimates the oxidation degree as the content of total carbonyl compounds was monitored using Fourier transform infrared spectroscopy-attenuated total reflectance. The changes in the surface composition due to the oxidation were confirmed by electron spectroscopy for chemical analysis. The extent of oxidation decreased with increasing zirconia content, which was attributed to the increased crystallinity as well as the decreased polymer portion of the UHMWPE/zirconia composites.

Kinetics of ethylene polymerization reactions with chromium oxide catalysts

Principal kinetic data are presented for ethylene homopolymerization and ethylene/1-hexene copolymerization reactions with two types of chromium oxide catalyst. The reaction rate of the homopolymerization reaction is first order with respect to ethylene concentration (both for gas-phase and slurry reactions); its effective activation energy is 10.2 kcal/mol (42.8 kJ/mol). The r1 value for ethylene/1-hexene copolymerization reactions with the catalysts is ∼30, which places these catalysts in terms of efficiency of α-olefin copolymerization with ethylene between metallocene catalysts (r1 ∼ 20) and Ti-based Ziegler-Natta catalysts (r1 in the 80–120 range). GPC, DSC, and Crystaf data for ethylene/1-hexene copolymers of different compositions produced with the catalysts show that the reaction products have broad molecular weight and compositional distributions. A combination of kinetic data and structural data for the copolymers provided detailed information about the frequency of chain transfer reactions for several types of active centers present in the catalysts, their copolymerization efficiency, and stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5315–5329, 2008