Heterogeneous Ziegler-Natta Catalysts Research Articles

Synthesis of Polar-functionalized Isotactic Polypropylenes Using Commercial Heterogeneous Ziegler-Natta Catalyst.

The efficient synthesis of polar-functionalized polypropylenes with high molecular weight and high stereoregularity represents a challenging task. This challenge becomes even more daunting when pursuing an industrially preferred heterogeneous process. This study demonstrated the realization of these goals through the use of commercial heterogeneous Ziegler-Natta catalysts in the copolymerization of propylene with ionic cluster polar monomers. The results revealed high copolymerization activity (∼1.1 × 107 g mol-1 h-1), moderate polar monomer incorporation ratios (∼4.9 mol %), high copolymer molecular weight (Mw > 105 g mol-1), high stereoregularity ([mmmm] ∼ 96%), and high melting temperature range (150-162 °C). The utilization of ionic cluster polar monomers improved the thermal stability as well as stereoselectivity of the catalyst. Moreover, the Ziegler-Natta catalyst can homopolymerize ionic cluster polar monomers with high activities (>104 g mol-1 h-1). The resulting polar-functionalized isotactic polypropylenes (iPP) exhibited superior tensile strength, impact strength, creep resistance, transparency, and crystallinity compared with nonpolar iPP. This enhancement was attributable to the dual roles of the ionic cluster polar monomer unit, serving as both a transparent nucleating agent and a dynamic cross-linking functionality. Furthermore, the polar-functionalized iPP exhibited improved compatibility with polar materials, offering benefits for applications in composites, recycling of mixed plastic wastes, 3D printing, and other fields. This study offered a comprehensive solution for the future industrial production of polar-functionalized iPP via copolymerization, bridging the gap between an efficient and practical copolymerization process from a synthetic chemistry perspective and enhanced material properties from an application perspective.

Deciphering the Role of Internal Donors in Shaping Heterogeneous Ziegler–Natta Catalysts Based on Nonempirical Structural Determination

Deciphering the Role of Internal Donors in Shaping Heterogeneous Ziegler–Natta Catalysts Based on Nonempirical Structural Determination

New Insights into the Nature of Ti(II) and Ti(III) Active Sites in the Heterogeneous Ziegler–Natta Catalyst

New Insights into the Nature of Ti(II) and Ti(III) Active Sites in the Heterogeneous Ziegler–Natta Catalyst

Influence of the synthetic procedure on the properties of three Ziegler-Natta catalysts with the same 1,3-diether internal donor

Being the main responsible for the huge production of polyolefins, heterogeneous Ziegler-Natta catalysts are among the most important catalysts in the chemical industry and they have been optimized over the years since their discovery in 1953 crossing many different generations. Lastly, catalysts of the 5th generation are characterized by the introduction in the pre-catalyst of 1,3-diether compounds as internal electron donors, which are stable in the presence of AlR3 activators and do not require the further addition of external donors during the following steps of the catalytic process to control the activity and selectivity. In this work, we synthetized and systematically investigated by a multi-technique approach three Ziegler-Natta catalysts characterized by the same 1,3-diether donor, but differing in the synthesis route. We found that the synthetic route influences the MgCl2 particle size, as well as the properties of the Ti species. In particular, the reprecipitation method brings the smallest MgCl2 particles and the most positive Ti4+ sites in the pre-catalyst, but also the largest amount of accessible Ti3+ sites after TEAl activation. These structural and spectroscopic data correlate pretty well with the kinetic of gas-phase propylene polymerization in very mild conditions.

Trouble-free combination of ω-alkenylmethyldichlorosilane copolymerization-hydrolysis chemistry and metallocene catalyst system for highly effective and efficient direct synthesis of long-chain-branched polypropylene

This paper reports a highly effective and efficient synthesis of long-chain-branched polypropylene (LCB-PP) rendered by combination of ω -alkenylmethyldichlorosilane copolymerization-hydrolysis (ACH) chemistry and metallocene catalyst system. The potential side reaction, the dichlorosilane-methylaluminoxane (MAO) double replacement reaction, is revealed to be slow-occurring and largely suppressible by slightly increasing the steric hindrance of the alkyl substituent(s) on the reactants. Thus, with 5-hexenylmethyldichlorosilane and 7-octenylmethyldichlorosilane of some increased alkenyl chain lengths, the main/side reaction competition dynamics in ω -alkenylmethyldichlorosilane/propylene copolymerization with metallocene ( rac -Me 2 Si-[2-Me-4-Ph(Ind)] 2 ZrCl 2 )-modified MAO complex involving the dichlorosilane-MAO double replacement reaction could shift disproportionally to the main copolymerization to the extent that the effect of the side reaction is not detectable. The synthesized LCB-PPs are characterized by narrow molecular weight distribution, with the LCB structure being H-shape and the interlinkage well defined as 1,2-dihydroxylsiloxane. The successful combination of ACH chemistry and metallocene catalyst system based on conventional metallocene and MAO assures a facile, well-defined, and, most importantly, highly effective and efficient synthesis of H-shape LCB-PP, as compared to two existing outstanding chemistries rendering the same type of LCB-PP, including ACH chemistry combined with heterogeneous Ziegler-Natta catalyst system and nonconjugated α,ω -diolefin copolymerization (NDC) chemistry exercised with 1,9-decadiene and metallocene catalyst system. • ω -Alkenylmethyldichlorosilane copolymerization-hydrolysis chemistry is successfully combined with metallocene catalyst system. • The dichlorosilane-MAO double replacement reaction is weak with ω -alkenylmethyldichlorosilanes of increased alkenyl lengths. • The chemistry results in highly effective and efficient synthesis of H-shape LCB-PP.

Physical Properties of Isotactic Polypropylene Blended with Less Crystalline Polypropylene

AbstractThe physical properties of polymeric materials, which are mixtures of various molecules, are determined by the sum of their contributions. Industrially important isotactic polypropylene (iPP), which is produced using heterogeneous Ziegler–Natta catalysts, shows broader distributions of molecular weight and stereoregularity because of the multisite nature, compared to molecular catalysts. However, systematic studies on the effects of these distributions on physical properties are lacking, especially for variations in stereoregularity. In this study, polypropylene (PP) additives with various molecular weights and stereoregularities (and their distributions) are added to an iPP matrix to clarify the effects of low‐concentration components on the overall physical properties. The results indicate the importance of incorporating the PP additives into the crystal structure of the iPP matrix.

Ultra-high molecular weight polyethylene: preparation and applications

Ultra-high molecular weight polyethylene is a kind of popular engineering material because of its unique properties stemming from high molecular weights. Nowadays, the preparations and applications of this type of material are widely researched. This review mainly focuses on the preparation of ultra-high molecular weight polyethylene using three types of typical catalysts (heterogeneous Ziegler-Natta catalysts, Fujita’s catalysts and α-Diimine Nickel (II) catalysts) and applications in two significant areas (bulletproof membranes and lithium-ion batteries). Ziegler-Natta catalysts and Fujita’s catalysts favor the synthesis of linear ultra-high molecular weight polyethylene, but α-Diimine Nickel (II) catalysis favors β-hydride elimination which leads to branched products. Changes in steric, composition, activators, temperature and pressure will affect the tendency towards different mechanisms and influence structures and properties of final products.

Characterization of Electronic Properties of Titanium Atom in Heterogeneous Ziegler-Natta Catalyst Analyzed by Soft X-ray Emission Spectrometry (SXES)

Abstract An advanced spectroscopic analysis by Soft X-ray Emission Spectrometry (SXES) was applied for the first time to the characterization of a heterogeneous Ziegler-Natta catalyst, which comprised TiCl4 and dibutylphthalate (DBP) supported on MgCl2. The high energy resolution capability of SXES made it possible to quantitatively detect outermost shell orbit signals of Lα at 452 eV and Lβ at 458 eV of Ti atom. These were assigned to Ti species interacting with DBP and MgCl2, respectively. From the correlation between the signal intensity ratios and the catalytic performances, it was presumed that Ti species interacting with MgCl2 should work as active sites for propylene polymerization.

Effect of processing conditions and catalyst type on the thermal oxidative degradation mechanisms and melt stability of metallocene and Ziegler‐catalyzed ethylene‐1‐hexene copolymers

AbstractPolyolefins have traditionally been polymerized via the heterogeneous Ziegler Natta (Z‐N) catalysts since their discovery in the 1950s, but the later developments of the homogeneous single site metallocene/methylaluminoxane (MAO) catalysts have opened the possibility for the synthesis of polyolefin polymers and copolymers (commercialized in the 1990s) with highly defined microstructure and great degree of control of their molecular architecture resulting in some unique beneficial properties compared to their Z‐N counterparts. The main aim of the work reported here was to examine critically the effects of the processing conditions during multipass extrusions on the molecular and rheological characteristics of metallocene‐catalyzed linear low density polyethylene and a Ziegler‐Natta‐based counterpart polymer and on the thermoxidative (in the melt) stability of their melts and their stabilization. Both polymers examined here were based on ethylene‐1‐hexene copolymers and produced by the same manufacturer with similar density and melt index (MI) values. The melt stability and rheological properties of the polymers were determined from melt flow and capillary rheometric measurements. The molecular characteristics were investigated using GPC for molecular weight determination, 13C‐NMR for short chain branching, 1H‐NMR and FTIR for the type and concentration of unsaturation groups, FTIR for carbonyl‐containing compounds and chemical analysis for hydroperoxide determination. The processibility of the two polymers was compared through examination of different processing conditions (die temperatures 210–285°C, screw speeds 50–200 rpm) used for a multipass extrusion process. Further, the effects of the processing conditions on the melt thermoxidation of the differently catalyzed LLDPE polymers were investigated. The results demonstrated that both the catalyst type and the processing conditions have a great effect on both the rheological and the themoxidative behavior of the polymers as well as on the balance between the competing oxidative reactions taking place in the polymer melt, for example, chain scission and crosslinking reactions. The results obtained for the different multipass extrusion conditions of the two polymers have illustrated clearly that the degradation mechanisms during their melt processing are substantially different. The melt degradation route of the Ziegler‐catalyzed polymer was shown to be dominated by chain scission reactions under all the processing conditions examined, and more so at the higher shear rates and temperatures. By contrast, the evidence clearly showed that the metallocene‐catalyzed polymer gave rise to crosslinking reactions that predominated even under the more severe processing conditions, that is, higher temperatures and shear rates.

Bottom-Up Synthesis of Multi-Grained Ziegler–Natta Catalyst Based on MgO/MgCl2/TiCl4 Core–Shell Catalyst

Morphology control plays a major role in the design of solid catalysts. Since the heterogeneous Ziegler–Natta catalyst (ZNC) is based on the in situ synthesis of MgCl2 support in a top-down manner, the individual control of the exterior and the interior structure of the catalyst macro-particles is challenging. In this study, we successfully prepared a ZNC with a multi-grain interior structure by the spray-drying of MgO nanoparticles, inspired by the fact that the MgO/MgCl2/TiCl4 core–shell catalyst can maintain the morphology of the raw MgO nanoparticles. This catalyst is the first example of the bottom-up preparation of MgCl2-supported ZNC. Here, we report its basic preparation method, characterization results, and performance in the homo-polymerization of ethylene and propylene, and copolymerization with 1-hexene.

Spectroscopic Signature and Structure of the Active Sites in Ziegler-Natta Polymerization Catalysts Revealed by Electron Paramagnetic Resonance.

Despite decades of extensive studies, the atomic-scale structure of the active sites in heterogeneous Ziegler-Natta (ZN) catalysts, one of the most important processes of the chemical industry, remains elusive and a matter of debate. In the present work, the structure of active sites of ZN catalysts in the absence of ethylene, referred to as dormant active sites, is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl3 so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Using electron paramagnetic resonance (EPR) and NMR spectroscopies, in particular 2D HYSCORE experiments complemented by density functional theory (DFT) calculations, we show that the activated ZN catalysts contain bimetallic alkyl-Ti(III),Al species whose amount is directly linked to the polymerization activity of MgCl2-supported Ziegler-Natta catalysts. This connects those spectroscopic signatures to the active species formed in the presence of ethylene and enables us to propose an ethylene polymerization mechanism on the observed bimetallic alkyl-Ti(III),Al species based on DFT computations.

Effect of AlEt2Cl on the polymerization of isoprene using TiCl4/MgCl2 type Ziegler-Natta catalyst: A DFT study

• The interaction between AlEt 2 Cl and MgCl 2 support was studied by the counterpoise corrected approach. • The mechanism of the polymerization of isoprene with heterogeneous Ziegler-Natta catalyst was first investigated by DFT. • The presence of AlEt 2 Cl improved the stereoselectivity of the active center. Alkylaluminium is one of the components of the Ziegler-Natta catalysts, which plays a significant role in the active materials with different regions and stereoselectivity. The polymerization of isoprene with alkylaluminium in TiCl 4 /MgCl 2 type Ziegler-Natta catalysts system is rarely studied by simulation. In this work, density functional theory (DFT) was applied to investigate the mechanism of the polymerization of isoprene with heterogeneous Ziegler-Natta catalyst in the presence and absence of AlEt 2 Cl on the surface of MgCl 2 (110). The interaction between AlEt 2 Cl and MgCl 2 support was studied by the counterpoise corrected approach. Two active models were adopted to analyze the influence of AlEt 2 Cl on the polymerization of isoprene in the coordination process and the insertion process respectively. The calculations indicated that only one double bond of isoprene was coordinated to the active center, the presence of AlEt 2 Cl improved the stereoselectivity of the active center, increased the difficulty of cis coordination, and reduced the difficulty of trans coordination. In the insertion process, the cis insertion process was more favorable and the trans product structure was more stable.

Insight into structural distribution of heterogeneous Ziegler–Natta catalyst from non-empirical structure determination

A structural distribution is an intrinsic nature of TiCl4-capped MgCl2 nanoplates, and its comprehension would uncover the origin of distributions in the primary structure of polyolefins produced by Ziegler–Natta catalysts. Such fundamental understanding is one of the prerequisites of the systematic design of catalysts. Here, we performed a series of machine learning-aided structure determination for TiCl4-capped MgCl2 nanoplates of different sizes and chemical compositions. Structural and electronic distributions of TiCl4 were analyzed on the basis of 106 structures, which were obtained in the course of the structure determination. Such a systematic investigation revealed that i) TiCl4 tends to adsorb on {110} surfaces as mononuclear species, while adsorption on {100} is not negligible, and that ii) even within the same mononuclear species on {110} surfaces, the steric environment and charge state of TiCl4 are distributed. A preliminary examination on ethylene insertion suggested that the TiCl4 distribution would generate the polymer primary structure distribution obtained by Ziegler–Natta catalysts.

Structural Disorder of Mechanically Activated δ-MgCl2 Studied by Synchrotron X-ray Total Scattering and Vibrational Spectroscopy

A combination of synchrotron X-ray total scattering and molecular simulation is a powerful approach for reliable determination of the structure of δ-MgCl2 as an indispensable component of heterogeneous Ziegler–Natta catalysts. Here, the same approach is applied to mechanically activated MgCl2. Four types of mechanically activated MgCl2 samples are prepared using ball-milling in the absence and presence of different donors. The development of structural disorder along the grinding time is compared. It was found that the presence of donors accelerates the formation of δ-MgCl2 in an early stage of grinding, while elongated grinding eventually results in δ-MgCl2 with similar extents of structural disorder in the absence and presence of different donors. The FT-IR investigation consistently verified the morphological similarity between the firmly ground samples. Thus, the structure of δ-MgCl2 is likely governed by mechanical energy when sufficiently ground.

Isoprene polymerizations catalyzed by TiCl4/MgCl2 type Ziegler-Natta catalysts with different titanium contents

The isoprene polymerization kinetics by using TiCl4/MgCl2 type Ziegler-Natta catalysts (TMC) with different titanium contents were studied for better understanding the possible active-specie structures of heterogeneous Ziegler-Natta (Z-N) catalysts for conjugated diene polymerizations. The catalytic features including the catalytic activity (CA), number of active centers ([C*]/[Ti]), rate constant for polymerization (kp), stereoregularity of these TMC catalysts were studied. The low titanium content catalyst TMC-1 (Ti = 0.09 wt.%) with more isolated mononuclear titanium species showed higher CA and yielded cis-1,4-/trans-1,4- mixed microstructure polyisoprene with low molecular weight (Mw) in the initial polymerization stage. The medium high titanium content catalyst TMC-2 (Ti = 2.38 wt.%) with more clustered mononuclear titanium species showed lower CA and yielded cis-1,4-/trans-1,4- mixed microstructure polyisoprene with high Mw in the early stage of polymerization. The high titanium content catalyst TMC-3 (Ti = 3.76 wt.%) presented lowest CA and yielded high trans-1,4- polyisoprene with higher Mw.

Direct Synthesis of High-Melt-Strength Polypropylene Using the Fourth Generation Heterogeneous Ziegler–Natta Catalyst and Commercial Production Process

The most of commercial isotactic polypropylene (PP) polymers exhibit low melt strength due to lack of a long-chain-branched (LCB) structure, which significantly limits PP processing operations. The...

Entanglement Formation Mechanism in the POSS Modified Heterogeneous Ziegler–Natta Catalysts

Chain entanglement was very important for adjusting the processability and mechanical property of nascent ultrahigh molecular weight polyethylene (UHMWPE). So far, it is still a mystery to unravel ...

High-precision Molecular Modelling for Ziegler-Natta Catalysts

A major bottleneck of computational chemistry in heterogeneous catalysis is found at the difficulty and resultant inaccuracy of molecular models for catalyst surfaces. Here, we review our recent efforts to establish a high-precision molecular model of heterogeneous Ziegler-Natta catalysts for olefin polymerization, which was mainly based on the validation of potential molecular models for a set of experimentally known facts in density functional calculations. The coadsorption of donor molecules with Ti mononuclear species on MgCl2 surfaces is proposed as an experimentally consistent molecular model, and its successful utilization in a structure-performance relationship study for donors is described.

Trans-1,4- stereospecific copolymerization of isoprene and butadiene catalyzed by TiCl4/MgCl2 type Ziegler-Natta catalyst II. Copolymerization Kinetics and Mechanism

Stereospecific copolymerization mechanism of isoprene (Ip) and butadiene (Bd) with heterogeneous TiCl4/MgCl2-Al(i-Bu)3 Ziegler-Natta catalyst was investigated for the first time in this paper. Copolymerization kinetics of isoprene and butadiene revealed that copolymers with high cis-1,4 units were observed in the initial stage, then the trans-1,4/cis-1,4 ratio increased gradually to the finally dominant trans-1,4-sequecnc with increasing polymerization time. The Al/Ti ratio influenced the catalytic efficiency, trans-1,4-sequecnc percentage and the butadiene incorporation (FBd). The copolymers obtained at different conversion and Al/Ti ratio were isolated to a series of fractions by stepwise isothermal crystallization fractionation from 80 °C to −20 °C. The trans-1,4-unit percentage, trans-trans and trans-cis placement, butadiene-isoprene (BI or IB) dyad sequence concentration, FBd, molecular weight and molecular weight distribution of the main fractions were analyzed by 1H NMR,13C NMR, TGA, GPC, DSC and WAXD characterization, which provided powerful evidences for the presence and evolution of active centers with different catalytic stereospecificity. Therefore, the possible active centers and trans-1,4 stereospecific copolymerization mechanism of isoprene and butadiene using heterogeneous Ziegler-Natta catalyst system was proposed accordingly.

Trans-1,4- stereospecific polymerization of isoprene with MgCl2-supported Ziegler-Natta catalyst I. Initial polymerization kinetic and polymerization mechanism

In order to understand the trans-1,4 stereospecific polymerization mechanism of conjugated dienes with the heterogeneous Ziegler-Natta catalyst, isoprene polymerization kinetics at different polymerization temperature in the initial polymerization stage and the microstructures of polymers and its fractions were studied in this work. Both polymerization temperature and time influenced the polymerization behavior greatly. The nascent polyisoprene (30s) with unusual high cis-1,4-units was observed and then the trans-1,4/cis-1,4 ratio of the polymers increased obviously to finally trans-1,4-dominated (96 mol%) with the increase in polymerization time. Fractions of the products based on the different crystallizability at different temperature were isolated and characterized by 1H-NMR, 13C-NMR, GPC and DSC. The nascent polyisoprene under 30s polymerization time was mainly composed by fractions A and G with 30–60 mol% trans-1,4-units and 2–26 mol % trans-cis dyad linkages. Active species with low stereoregularity may contribute to theses fractions. While fractions D and E with high trans-1,4 unit (>96 mol%) from active species with high stereoregularity were growing to the predominated components with increased conversion. At least two kinds of active species with different stereospecificity and lifetime were proposed to explain the isoprene polymerization with heterogeneous TiCl4/MgCl2-Al(i-Bu)3 catalyst. Effects of temperature on cis/trans-1,4 structure were discussed. Hopely, this research would provide a further understanding about trans-1,4 stereospecific polymerization of conjugated dienes with heterogeneous Ziegler-Natta type catalysts.