Ziegler-Natta Catalyst Systems Research Articles

Orbital-scale understanding of the surface effect of the MgCl2 in the Ziegler–Natta catalyst for ethylene polymerization: A computational study

Ziegler-Natta catalyst is a widely used olefin polymerization catalyst in petrochemical industries. However, the role of each catalyst component is not clear due to the complexity of composition and structure. MgCl2 is a suitable support for Ziegler-Natta catalyst because its crystal structure is similar to that of TiCl3, and the surface effect of MgCl2 in Ziegler-Natta catalyst system was explored in ethylene polymerization at the orbital scale. A series of the stable surface-supported catalysts with unsaturated coordination Mg2+ were used to simulate the mechanism of ethylene polymerization by the periodic density functional theory. This study found that MgCl2 with different surfaces regulates the activity of the catalyst by adjusting the d band centre of the catalyst active centre. This concept can be used to explain the surface effect of support in general catalysts.

Modelling and parameter estimation of trans‐β‐farnesene coordination polymerization

Abstracttrans‐β‐Farnesene is a bio‐derived terpene monomer that can polymerize, generating polymers with properties that can be similar to the properties of conventional petroleum‐derived polymers. For this reason, in the present study, several coordination polymerizations of trans‐β‐farnesene are carried out using the Ziegler–Natta catalyst system composed by neodymium versatate (), diisobutylaluminum hidride (DIBAH), and dimethyldichlorosilane (DMDCS) in order to evaluate the influence of key operation variables on the control of average molar masses and monomer conversion. A phenomenological model is proposed to describe the coordination polymerization of trans‐β‐farnesene, and the kinetic parameters required to simulate the reactions are estimated. The initial concentration of DIBAH used as a chain transfer agent (CTA) is calculated by a data reconciliation procedure since this very active compound can participate in undesired side reactions. It is shown that the initial monomer, DIBAH, and concentrations exert strong influences on the monomer conversion and average molar masses of (poly)farnese while the temperature effect is not so pronounced. The proposed kinetic mechanism was able to predict well the experimental data collected during the reactions, with the successful reconciliation of CTA concentrations and estimation of model parameters.

Customizing the comonomer incorporation distribution in Ziegler–Natta‐based LLDPE: Harnessing the influences of the titanation temperature during catalyst synthesis and of polymerization process parameters

AbstractThe microstructure of linear low‐density polyethylene (LLDPE) is strongly influenced by short‐chain branches (SCBs) incorporated into the polymer backbone. Varying the number, distribution, and length of SCBs allows the properties of the resulting polymer to be tailored to meet specific requirements. Using Ziegler–Natta (ZN) catalysts for synthesis has disadvantages in terms of the comonomer incorporation distribution (CID) compared to, for instance, metallocene and post–metallocene catalysts. Nevertheless, ZN catalysts continue to be widely used, as many of the new generations of catalysts are more difficult to handle and cannot match the cheap cost of ZN catalysts. To improve this aspect of ZN catalysts, we investigated the influence of catalyst titanation temperature and polymerization process parameters on the CID. Our results show that it is possible to manipulate the process parameters of the present ZN catalyst system to yield a desired comonomer amount and CID in the polymer. Varying the titanation temperature clearly influenced the titanium content of the catalyst. Molecular‐weight distribution analysis and deconvolution results indicate that changes in the amounts of comonomer incorporated and in the CID are directly related to the catalyst's active site that produces the lowest‐molecular‐weight fraction.

β‐Myrcene Coordination Polymerization: Experimental and Kinetic Modeling Study

AbstractThe present work presents phenomenological models to describe the coordination polymerization of β‐myrcene using the Ziegler–Natta catalyst system composed by neodymium versatate (NdV3), diisobutylaluminum hydride (DIBAH), and dimethyldichlorosilane. The kinetic parameters required to simulate the reactions are estimated, and the amount of DIBAH used as a chain transfer agent (CTA) is obtained by a data reconciliation strategy since it can participate in side reactions. Several experiments are performed at different conditions to evaluate the impact of key operation variables on the control of monomer conversion and average molar masses. It is shown that the initial NdV3, β‐myrcene, and DIBAH concentrations exert strong influences on the course of the polymerization. The kinetic mechanism of Coordinative Chain Transfer Polymerization (CCTP) fits well with the data of final average molar masses and monomer conversion, while the dynamic trajectories of these variables are fitted better by kinetic mechanisms of more conventional coordination polymerizations, considering site deactivation and termination by chain transfer. In all cases, the proposed models are able to predict the experimental data well after successful parameter estimation and reconciliation of CTA concentrations, indicating that the kinetic mechanism can be characterized by different kinetic regimes.

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.

Synthesis, Structural Studies, and Application of Aluminum Aryloxides for Ring-Opening Metathesis Polymerization

A series of aluminum aryloxides of types [Al(OAr)3] and [Al(OAr)2Cl] (Ar = 4-CH3C6H4, 4-PhC6H4, 2-iPr-C6H4, 2-tBu-C6H4, 2,6-iPr2C6H3, and 2,6-Cl2C6H3) were synthesized from commercially available reagents and structurally characterized by single X-ray diffraction studies. The structural evaluations for aluminum aryloxides revealed the formation of dinuclear clusters in the solid state. The solution behavior of the synthesized compounds was studied by multinuclear nuclear magnetic resonance (NMR) spectroscopy. The synthesized compounds were applied for the in situ generation of Ziegler–Natta catalyst systems for the ring-opening metathesis polymerization (ROMP) of nonconstrained olefins. The ligand exchange between WCl6 and Al-aryloxides followed by activation with aluminum alkyls resulted in the formation of ill-defined species showing enhanced ROMP reactivity compared to the related systems generated upon the ligand exchange between WCl6 and ArOH or isolated [W(OAr)4Cl2]. The benefits of using newly developed systems for the ROMP of cyclic olefins are their low costs and high molecular weights for polymerization products (Mw > 250 kDa). Moreover, an E/Z stereoselective control over the double C═C bond in the polymeric product was achieved upon tuning the steric volume at the aryloxide ligand framework.

Coordinative Chain Transfer Polymerization of Sustainable Terpene Monomers Using a Neodymium-Based Catalyst System.

The present investigation involves the coordinative chain transfer polymerization (CCTP) of biobased terpenes in order to obtain sustainable polymers from myrcene (My) and farnesene (Fa), using the ternary Ziegler–Natta catalyst system comprising [NdV3]/[Al(i-Bu)2H]/[Me2SiCl2] and Al(i-Bu)2H, which acts as cocatalyst and chain transfer agent (CTA). The polymers were produced with a yield above 85% according to the monomeric consumption at the end of the reaction, and the kinetic examination revealed that the catalyst system proceeded with a reversible chain transfer mechanism in the presence of 15–30 equiv. of CTA. The resulting polyterpenes showed narrow molecular weight distributions (Mw/Mn = 1.4–2.5) and a high percent of 1,4-cis microstructure in the presence of 1 equiv. of Me2SiCl2, having control of the molecular weight distribution in Ziegler–Natta catalytic systems that maintain a high generation of 1,4-cis microstructure.

Nitrogen Poisoning of HDPE and LLDPE based on Chemically Recycled Post‐Consumer Plastic via a Kinetic and Microstructural Modeling Technique

AbstractChemical recycling of plastic waste has promise as a complementary technology to increase eco‐efficiency of plastics life cycles. Accumulation of impurities in feed streams can affect sensitive compounds such as the Ziegler–Natta catalyst systems commonly used to produce polyolefins such as high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). In a poison study, the influence of impurities—more specifically NO and N2O—on the catalyst system are investigated comprehensively in terms of kinetic behavior and activity rates. A product composition analysis gives insights into product properties such as molecular weight distribution (MWD), comonomer composition distribution (CCD), melting point, and crystallinity. By applying known modeling techniques (kinetic modeling, MWD, and CCD deconvolution modeling), information beyond analytical data is obtained. The results of the study show that both poisons significantly affect catalyst kinetics and reduce catalyst activity. N2O influences primarily the MWD, while NO poisoning strongly affects the CCD of LLDPE samples. Since the mechanical properties of the polymers produced depend on factors such as MWD and CCD, NO and N2O poisoning may reduce their processability and applicability.

Influence of Poisons Originating from Chemically Recycled Plastic Waste on the Performance of Ziegler–Natta Catalysts

AbstractChemically recycled monomer feed streams from postconsumer plastic packaging waste are expected to contain impurities that act as catalyst poisons. This work investigates the impact of such impurities on a commercial fourth‐generation Ziegler–Natta catalyst system. A recycled monomer feed stream in two different procedures by adding representative catalyst poisons (pyridine and n‐butanol) in various quantities to the reactor setup is simulated. Measuring catalyst activity and molecular weight distribution (MWD) and performing kinetic and MWD deconvolution modeling, the impact of the catalyst poisons on polymer product properties at the microstructural level is evaluated. The results demonstrate that, beyond a certain concentration (120 ppm), catalyst poisons have a substantial impact on the activity levels of the catalyst system tested. MWD deconvolution modeling shows an influence of the poisons on the composition of the resulting polymer product in the form of a shift toward lower or higher molecular weights (depending on the procedure). This microstructural analysis highlights the importance of purifying chemically recycled monomer feed streams.

Progress in MgCl2 supported Ziegler-Natta catalyzed polyolefin products and applications

The innovation of Ziegler-Natta (Z-N) catalysts opened a novel aspect of chemistry in terms of polyolefin formation. Significant progress of more than fifty years in catalytic olefin polymerization simplified polyolefin production by optimizing the reaction conditions and internal donors. In this review, we particularly emphasized on recent development on different internal donor based Z-N catalyst systems, the role of external electron donors and co-catalyst chemistry. Furthermore, the Ziegler-Natta catalyst system, polymerization reaction, and polymer process technologies gradually upgrading to produce different polyolefin products. In particular, polyolefin fibers, composites, foam, blends and polyolefin-based 3D-printing products targeted in this review for substantial benefits of both society and highly diversified industries.

Preparation and crystalline transformation of functionalized poly(1-butene) containing PFPU and mPEG side chain

A series of 1-butene/pentafluorophenylundec-1-ene ester random copolymers were synthesized under the Ziegler–Natta catalyst system. The content of the pentafluorophenyl (PFP) group in the copolymer can reach up to 0.59 mol%. The DSC test found that the PFP groups attached to the PB main chain retard the crystalline transformation of Form II to Form I. Nucleophilic aromatic substitutions of pentafluorophenyl ester occurred with biocompatible poly(ethylene glycol) methyl ether (mPEG) introduced into the side chain of PB under very mild conditions. The results show that not only is the crystallization rate of mPEG functionalized PB increased, but also Tm, Tc, χc and the crystalline phase transition rate of Form II to Form I are also enhanced. Among them, mPEG with a Mn of 500 has the best promoting effect. On the other hand, the hydrophilicity of mPEG-functionalized PB is improved, and it is proportional to the chain length of mPEG. However, the experimental results show that the regularity of the PB structure is the determinant of the rate of crystallization and phase transition.

High Throughput Experimentation Protocol for Quantitative Measurements of Regioselectivity in Ziegler–Natta Polypropylene Catalysis

This paper introduces a high throughput experimentation method for fast and accurate evaluations of regioselectivity in Ziegler–Natta (ZN) propene polymerizations. With a simple protocol, the (very low) fraction of regio-irregular 2,1 monomeric units in the polymers can be quantitated by means of 13C NMR chain-end analyses on single H2-terminated polypropylene samples. The method, that was successfully validated for three representative ZN catalyst systems, also provides information on catalyst “dormancy” and propensity to undergo chain hydrogenolysis. This opens the door to the rapid and accurate implementation of quantitative structure–activity relationship (QSAR) databases of regioselectivity and “hydrogen response” in this important industrial catalysis.

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.

Effect of multi-ethers and conventional alkoxysilanes as external donors on the 4th generation Ziegler-Natta catalysts for propylene polymerization

The multi-ether compounds with different numbers of methoxy groups containing 1,3-dimethoxy-2,2-bis(methoxymethyl)propane and 1-methoxy-2,2-bis(methoxymethyl)butane were synthesized using the Williamson reaction from pentaerythritol and 1,1,1-tris(hydroxymethyl)propane, respectively, in the presence of sodium hydride and methyl iodide in tetrahydrofuran and they were characterized by 1H NMR, 13C NMR, and FTIR spectroscopy. These compounds were employed as external donors in the polymerization of propylene using the industrial Ziegler-Natta catalyst. A commercial spherical MgCl2-supported Ziegler-Natta catalyst containing diisobutyl phthalate as the internal donor was used for the polymerization of propylene. The role of ether compounds and industrial alkoxysilanes on the properties of polypropylene were studied using the xylene solubility method, melt flow index, gel permeation chromatography, scanning electron microscopy, and differential scanning calorimetry. The addition of the electron donors has led to improvements in the activity and selectivity of the Ziegler-Natta catalyst system.

Optimal Catalyst and Cocatalyst Precontacting in Industrial Ethylene Copolymerization Processes

In industrial-scale catalytic olefin copolymerization processes, catalyst and cocatalyst precontacting before being introduced in the polymerization reactor is of profound significance in terms of catalyst kinetics and morphology control. The precontacting process takes place under either well-mixing (e.g., static mixers) or plug-flow (e.g., pipes) conditions. The scope of this work is to study the influence of mixing on catalyst/cocatalyst precontacting for a heterogeneous Ziegler-Natta catalyst system under different polymerization conditions. Slurry ethylene homopolymerization and ethylene copolymerization experiments with 1-butene are performed in a 0.5 L reactor. In addition, the effect of several key parameters (e.g., precontacting time, and ethylene/hydrogen concentration) on catalyst activity is analyzed. Moreover, a comprehensive mass transfer model is employed to provide insight on the mass transfer process and support the experimental findings. The model is capable of assessing the external and internal mass transfer limitations during catalyst/cocatalyst precontacting process. It is shown that catalyst/cocatalyst precontacting is very important for the catalyst activation as well as for the overall catalyst kinetic behavior. The study reveals that there is an optimum precontacting time before and after which the catalyst activity decreases, while this optimum time depends on the precontacting mixing conditions.

Promoting ethylene polymerization through cocatalyst modification

Effect of chlorocyclohexane (CHC) on ethylene polymerization using MgCl2/TiCl4/TEA Ziegler–Natta catalyst system was studied, where MgCl2, TiCl4, and TEA (triethyl aluminum) were used as support, catalyst, and activator, respectively. The polymerization rate, catalyst activity, and produced polymer were significantly affected by the presence of CHC as a promoter. This study strongly indicates that CHC will act as a promoter with high performance in the ethylene polymerization. There was a remarkable increase in the catalyst yield and polymerization rate, particularly, in the presence of hydrogen which was used for controlling the molecular weight. A reduction in the polymer molecular weight was observed in the presence of CHC and hydrogen. The amount of the produced wax as a byproduct noticeably reduced. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution.

High Melt Strength Polypropylene with Wide Molecular Weight Distribution Used as Basic Resin for Expanded Polypropylene Beads

The high melt strength polypropylene (HMSPP) is fabricated by direct polymerization through controlling the species and ratios of the external electron donors in the Ziegler–Natta catalyst system at different reaction stages. The polypropylene exhibits wide molecular weight distribution and higher melt strength. The expanded polypropylene (EPP) beads are prepared by the above HMSPP through an autoclave-based batch process. The effects of melt strength on the cellular morphology of EPP are investigated by scanning electron microscope and melt strength meter, respectively. Results indicate higher melt strength facilitates the control of the foaming process and the cellular structure compared with a commercial propylene homopolymer such as T03. The bimodal cell structure is obtained with the single foaming agent CO2 in both of the EPP beads from HMSPP and commercial polypropylene.

Donor Decomposition by Lewis Acids in Ziegler–Natta Catalyst Systems: A Computational Investigation

The development of new donors (Lewis bases, usually containing oxygen atoms) is one of the chief areas of research in Ziegler–Natta (ZN) olefin polymerization systems. The addition of such donors has led to improvement in the activity and selectivity of ZN systems. However, in order for the donor to be effective, it has to be chemically stable and resistant to decomposition by Lewis acidic species such as AlEt3. Discussed in the current work is the chemical stability of different ester donors, including aromatic benzoate donors and the silyl ester—a promising new donor class in ZN systems. Full quantum chemical calculations with density functional theory (DFT) indicate that esters can undergo decomposition through different pathways upon interaction with species such as the AlEt3 dimer: Al2Et6. Moreover, the studies show that the active, supported titanium catalyst species can cause donor decomposition and, in fact, is likely to be the greater threat to donor decomposition than Al2Et6. This explains why the addition of excess donors can lead to the poisoning of the active site in ZN systems. We have also computationally investigated means of improving the silyl ester donors in order to make them more robust and resilient to donor decomposition by Al2Et6 and the supported active titanium species.

Novel fabrication route for porous silicon carbide ceramics through the combination of in situ polymerization and reaction bonding techniques

ABSTRACTFor the first time, an in situ polymerization technique was applied to produce mullite‐bonded porous SiC ceramics via a reaction bonding technique. In this study, SiC microsized particles and alumina nanopowders were successfully coated by polyethylene (PE), which was synthesized from the particle surface in a slurry phase reactor with a Ziegler–Natta catalyst system. The thermal studies of the resulting samples were performed with differential scanning calorimetry and thermogravimetric analysis. The morphology analysis obtained by transmission electron microscopy and scanning electron microscopy (SEM) confirmed that PE was successfully grafted onto the particle surface. Furthermore, the obtained porous ceramics were characterized in terms of their morphologies, phase composition, open porosity, pore size distribution, and mechanical strength. SEM observations and mercury porosimtery analysis revealed that the quality of the dispersion of nanosized alumina powder into the microsized SiC particles was strongly enhanced when the particles were coated by polymers with in situ polymerization. This resulted in a higher strength and porosity of the formed ceramic porous materials with respect to the traditional process. In addition, the X‐ray diffraction results reveal that the amount of mullite as the binder increased significantly for the samples fabricated by this novel method. The effects of the sintering temperature, forming pressure, and polymer content on the physical and mechanical properties of the final porous ceramic were also evaluated in this study. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40425.

Butyl chloride as promoter in ethylene polymerization by magnesium ethoxide‐supported catalyst

ABSTRACTThe effects of butyl chloride as a promoter in the ethylene polymerization were studied using a Mg(OEt)2/TiCl4/triethyl aluminum (TEA) Ziegler–Natta catalyst system, where Mg(OEt)2, TiCl4, TEA were used as support, catalyst, and activator, respectively. The influence of BC on the catalyst performance, polymerization rate, and polymer properties were investigated. This study strongly indicates that BC could act as a promoter with high performance in the ethylene polymerization. There was a remarkable increase in the catalyst yield and polymerization rate, in particularly, in the presence of hydrogen which was used for controlling the molecular weight. A reduction in the polymer molecular weight was observed in the presence of BC and hydrogen. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40189.