Ziegler-Natta 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.

Study of the Chemical Activities of Carbon Monoxide, Carbon Dioxide, and Oxygen Traces as Critical Inhibitors of Polypropylene Synthesis.

This study outlines the investigation into how the compounds CO2, CO, and O2 interact with the active center of titanium (Ti) on the surface of MgCl2 and how these interactions impact the productivity of the Ziegler-Natta catalyst, ultimately influencing the thermal stability of the produced polypropylene. The calculations revealed that the adsorption energies of Ti-CO2-CO and O2 were -9.6, -12.5, and -2.32 Kcal/mol, respectively. Using the density functional theory in quantum calculations, the impacts of electronic properties and molecular structure on the adsorption of CO, O2, and CO2 on the Ziegler-Natta catalyst were thoroughly explored. Additionally, the Gibbs free energy and enthalpy of adsorption were examined. It was discovered that strong adsorption and a significant energy release (-16.2 kcal/mol) during CO adsorption could explain why this gas caused the most substantial reductions in the ZN catalyst productivity. These findings are supported by experimental tests showing that carbon monoxide has the most significant impact on the ZN catalyst productivity, followed by carbon dioxide, while oxygen exerts a less pronounced inhibitory effect.

Experimental and Theoretical Insights into the Effect of Dioldibenzoate Isomers on the Performance of Polypropylene Catalysts.

Experimental investigations and density functional theory (DFT) calculations were carried out to study the comprehensive effect of different 3,5-heptanedioldibenzoate (HDDB) optical isomers as the internal electron donor on the catalytic performance of Ziegler-Natta catalysts. The experimental catalytic activity of HDDB has a positive correlation with the relative content of the mesomer incorporated during catalyst preparation, while the hydrogen response of HDDB displayed a negative correlation with the relative content of the mesomer. In order to apply the DFT calculation results to the macroscopic activity of the catalyst, the content of the active centers of the catalyst was analyzed. Assuming that the content of the active centers is proportional to the internal electron donor content of the catalyst, binary linear regression was carried out, which showed a good linear correlation between experimental activity data and internal electron donor content. Furthermore, the fitted activity of the single active centers aligned well with the calculated activation energies. These results revealed that the catalytic activity of polypropylene (PP) catalysts is dependent on both the active center content and the catalytic activity of an individual active center. Additionally, the lower hydrogen response of HDDB leads to a higher molecular weight of polypropylene obtained from the RS-containing catalyst compared to the SS-containing catalyst. Further study reveals that the hydrogen transfer reactions of 2,4-pentanediol dibenzoate (PDDB)/HDDB are influenced by the orientation of the methyl/ethyl groups in different isomers, which affect the activation energy differences between the hydrogen transfer reaction and the propylene insertion reaction, and finally influence the molecular weight of PP.

A comparative Monte Carlo simulation of HDPE synthesis with bimodal molecular weight distribution: evaluating slurry and solution processes using dual-site metallocene catalyst

ABSTRACT This research employed Monte Carlo simulation as a computational technique to investigate the copolymerization of ethylene and 1-butene in the presence of hydrogen, utilizing slurry and solution processes. A dual-site metallocene catalyst was utilized to synthesize high-density polyethylene (HDPE) with a bimodal molecular weight distribution (MWD). The solution process accelerated copolymerization rates and hydrogen transfer compared to the slurry. Furthermore, under equivalent conditions, the solution process exhibited a twofold higher level of 1-butene incorporation into copolymer chains. Elevating 1-butene partial pressure by 50% increased weight average molecular weight ( M ¯ w ) of copolymers by 15% in solution process and 5% in slurry process. Increasing 1-butene partial pressure expanded and shifted the bimodal distribution towards higher molecular weights in both processes. Elevated hydrogen partial pressure enhanced peak heights and shifted towards lower molecular weights, with the slurry process showing stronger effects. The solution process had a range of short-chain branching per 1000 carbon atoms (SCB/1000C) (15-40), approximately twice as large as the slurry process. The slurry process resulted in more regular chains with higher crystallinity (68.7%) compared to the solution process (66.4%).

Insight of co-catalyst and external donor for propylene polymerization in Ziegler–Natta catalysis: FT-NMR study

Insight of co-catalyst and external donor for propylene polymerization in Ziegler–Natta catalysis: FT-NMR study

Study of Heterogeneity of Ethylene/1-Octene Copolymers Synthesized with Zirconium and Titanium Complexes Bearing Diamine-bis(phenolate) Ligands.

A series of ethylene/1-octene copolymers synthesized with diamine-bis(phenolate) complexes activated with Al(iBu)3/[Ph3C][B(C6F5)4] were subjected to preparative temperature rising elution fractionation (TREF). The complexes used differed in the type of metallic center (Zr or Ti) or the amine donor in the pendant arm of the ligand (NMe2 or NiPr2). The obtained fractions were then characterized via FTIR, DSC and GPC methods. It was found that all the copolymers had very broad chemical composition distributions, and the most heterogeneous was the copolymer produced by the titanium complex bearing a ligand with the NiPr2 donor group. The difference in the comonomer incorporation into the macromolecules of the fractions was as high as 8.3 mol%. The melting temperature and molecular weight of the fractions changed nearly linearly with the increased elution temperature. Copolymers produced by zirconium catalysts were also fractionated by molecular weight using the solvent/non-solvent technique with subsequent analysis of the fractions. It was shown that the fractions have a similar composition, low molecular weight distribution and very broad comonomer distribution. Therefore, the comonomer content in the fractions was not a function of the molecular weight as was observed for the copolymers synthesized with the Ziegler-Natta catalysts.

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

The effects of a new aminosilane external donor on propylene polymerization with MgCl2-supported Ziegler-Natta catalyst

The effects of a new aminosilane external donor on propylene polymerization with MgCl2-supported Ziegler-Natta catalyst

Novel kinetic modeling strategy for industrial-scale UNIPOL polypropylene with Ziegler-Natta catalyst

Polypropylene (PP) is a synthetic resin with exceptional physical and chemical properties, making it suitable for various household and industrial applications. However, as the demand for PP continues to rise, the polypropylene industry faces challenges in improving its quality and efficiency. Developing an accurate mathematical model that describes the continuous polymerization process is crucial for enhancing PP production, as it is useful for controlling product quality and improving production efficiency. While previous studies have focused on modeling propylene polymerization using laboratory-scale and pilot-scale reactors, these models do not effectively apply to industrial-scale processes due to the complexity of the industrial environment. Therefore, a novel kinetic modeling method combining the modeling of the kinetic mechanism of the polymerization reaction with an intelligent optimization algorithm for the industrial-scale continuous gas-phase fluidized bed propylene polymerization process is proposed. To establish the kinetic mechanism model, the improved moments (MOM) method is utilized to derive a set of mass balance equations that account for various fundamental processes such as catalyst activation, chain initiation, chain growth, chain transfer to hydrogen, chain transfer to monomers, chain transfer to co-catalysts, and spontaneous deactivation. However, kinetic parameters serve as the link between the theoretical model and the actual production process, so the kinetic parameters estimation problem need to be transformed into a multi-objective problem by minimizing the least squares difference between the measurement data of the actual industry process and the predicted result of the kinetic model. Therefore, an improved multi-objective mayfly algorithm (IMOMA) is introduced to estimate the polymerization kinetic parameters, which incorporates the simulated binary crossover (SBX) operator and the polynomial mutation (PM) operator into the basic multi-objective mayfly algorithm (MOMA). Finally, by fitting industrial measurement data of the melt index (MI) and the polymerization rate (PR) of an actual polypropylene industrial case study, the proposed algorithm accurately determines the polymerization kinetic parameters. The results demonstrate that the MOM-IMOMA modeling approach outperforms other methods and holds significant promise for industrial-scale polypropylene production.

Effect of internal and external electron donors on stereospecific polymerization of isoprene with TiCl4/MgCl2 type Ziegler-Natta catalysts

Two TiCl4/MgCl2 type Ziegler-Natta catalysts containing ethyl benzoate (EB) and dibutyl phthalate (DBP) as internal electron donors (ID) were prepared for isoprene polymerizations using five kinds of external electron donors (ED) (phenyltrimethoxysilane (ED-1), dicyclopentyl(dimethoxy)silane (ED-2), 2-butyl-2-ethyl-1,3-dimethoxypropane (ED-3), 1,3-dimethoxypropane (ED-4) and di(2-ethylhexyl)phthalate (ED-5)). The structure features of TiCl4/ID/MgCl2 catalysts were characterized and the effect of ID and ED on polymerization behaviors was studied. EB had higher adsorption content on catalyst surface, higher catalytic activity and lower trans-1,4 stereoselectivity than DBP. Appropriate introduction of ED-1 and ED-2, expect ED-3, ED-4 and ED-5, caused the enhancement in polymerization activity and trans-1,4 content, while excess addition led to the deactivation. The effect of ED on equilibrium between selective activation and deactivation of active species significantly relied on the electron donor type and concentration.

Influence of Cocatalysts on the Performance of Postphthalate Supported Ziegler–Natta Catalysts in Gas-Phase Propylene Polymerization

Influence of Cocatalysts on the Performance of Postphthalate Supported Ziegler–Natta Catalysts in Gas-Phase Propylene Polymerization

Group 14 metallocene catalysts for carbonyl hydroboration and cyanosilylation

A series of six Group 14 metallocene compounds (M = Ge, Sn, Pb) were studied as catalysts for carbonyl hydroboration and cyanosilylation reactions at room temperature. Both bis(pentamethylcyclopentadienyl) and tetramethyldisiloxa[3]metallocenophane compounds were compared. The tin and lead metallocenophanes exhibited the highest reactivity in hydroboration and cyanosilylation reactions. Hammett analysis of aldehyde hydroboration provided a ρ value of 0.73, suggesting a buildup of negative charge during the turnover-limiting step, consistent with the transition state for hydride transfer to the carbonyl center. NMR studies of Lewis acidity indicate that the Ge, Sn, and Pb tetramethyldisiloxa[3]metallocenophane compounds are weak Lewis acids.

The role of organoaluminum and electron donors in propene insertion on the Ziegler-Natta catalyst.

Alkyl aluminium plays a primary role in activating Ti within Ziegler-Natta (ZN) catalysts for propylene polymerization. We performed density functional calculations to explore the additional roles of AlEt3 and AlEt2Cl, in conjunction with diisobutyl phthalate (DIBP) internal donor and dicyclopentyl dimethoxysilane (DCPDMS) external donor, to enhance the stereoselectivity of propene insertion. Based on our calculated adsorption energies on the (MgCl2)13/TiCl2iBu cluster model for the ZN catalyst, the presence of DIBP on the cluster essentially facilitated AlEt2Cl adsorption while AlEt2Cl also promoted the adsorption of DIBP. The reaction between AlEt3 and DIBP on the cluster led to the extraction of DIBP, creating an available site for DCPDMS adsorption. While the stereoselectivity, represented by the difference in the activation energies between 1,2-re and 1,2-si insertions of propene, was negligible on the cluster containing only DIBP, it became significant on the clusters containing both AlEt2Cl and DIBP (and DCPDMS). AlEt2Cl plays a pivotal role in imposing steric effects near the Ti active site, thereby increasing stereoselectivity. Our findings suggest the importance of including AlEt2Cl alongside DIBP (and DCPDMS) in the ZN cluster model to investigate stereoselective propene insertion. Considering AlEt2Cl adsorption and AlEt3 reaction with internal donors is essential in developing Ziegler-Natta catalysts.

Melt memory in random ethylene-1-alkene copolymers.

Chain flexibility or stiffness based polymer conformation plays a crucial role in affecting the dynamics and kinetics of polymers, which is related to the hierarchical architecture of chains. A series of random copolymers of ethylene and 1-alkenes including 1-hexene, 1-octene, and 1-dodecene were synthesized with metallocene catalysts. The crystallization behavior and memory effect in random ethylene-1-alkene copolymers with different side groups were investigated via differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). Rheological tests were performed for understanding their dynamical behavior. The results show that the melting peak and the viscosity decrease but the orthorhombic crystal dimensions increase with co-unit contents increasing in the copolymers. It was found that the scaling relationship between the zero shear viscosity (η0) and molecular weight (Mn) of the copolymers containing ethylene-1-hexene and ethylene-1-octene is 3.6, which is higher than the classical scaling value of 3.4. The memory of crystals in the melt is enhanced with the increase of 1-alkene contents but is independent of the types of 1-alkenes. The enhanced melt memory effect in the copolymers was proposed due to the effect of the 1-alkene based side groups on the dynamics of polymer chains. The present work would be helpful to understand the chain stiffness based polymer dynamics and processing of polyolefins and copolymers prepared with the metallocene catalyst.

МОДЕЛИРОВАНИЕ КИНЕТИКИ ЖИДКОФАЗНОЙ ПОЛИМЕРИЗАЦИИ ПРОПИЛЕНА НА ТИТАН-МАГНИЕВОМ КАТАЛИЗАТОРЕ

Polypropylene is one of the most widespread plastics in the world, widely used in various industries, including packaging, automotive, electronics and construction. In Russia, the use of polypropylene is also growing and plays an important role in various sectors of the economy. It is produced by polymerization of propylene on Ziegler-Nutt metal catalysts. Overheating of polymer particles, which can occur due to the exothermic nature of the polymerization process, negatively affects the kinetics of the process and the quality of the polymer. In this work, mathematical modeling of the process of liquid-phase polymerization of propylene on a titanium-magnesium catalyst was carried out in order to analyze the influence of reaction rates and mass transfer on the growth of polymer particles. The model with simplifications is considered, which provides analytical solutions of monomer material balance equations in the particle. This model contains equations for mass and heat transfer coefficients (βp, αp), equations of thermophysical properties of components and mixtures, such as heat capacity, density, thermal conductivity and viscosity of the mixture (Cp, ρ, λ, μ). It is analyzed how reaction and mass transfer rates influence the growth of polymer particles during liquid-phase polymerization of propylene on titanium-magnesium Ziegler-Natta catalyst, where the catalyst is titanium tetrachloride fixed on the surface of magnesium dichloride carrier. A mathematical model using Wolfram Mathematica was created based on the data obtained. It is found that for different values for which there are formulas in the model, it is possible to calculate and plot at different reaction temperatures and diameters of catalytic converter particles. The results obtained are used to predict and prevent overheating of particles in the process of polypropylene synthesis, which in turn contributes to the improvement of technical and economic indicators of the process. This model can be used to better understand the polymerization process and optimize reaction conditions. It can help in the development of new catalysts and polymerization methods, as well as in improving the properties of the resulting polymers.

Sulfonated porous organic polymer supported Ziegler-Natta catalysts for the synthesis of ultra-high molecular weight polyethylene.

Porous organic polymers (POPs) are attracting attention for their easy functionalization and potential as catalyst supports in olefin polymerization. In this study, sulfonated POP (s-POP) supported Ziegler-Natta catalysts were used for ethylene polymerization, producing ultra-high molecular weight polyethylene, with M ν reaching up to 6.83 × 106 g mol-1. The maximum M ν of polyethylene was achieved by Cat-3 with DIBP as the internal donor, albeit with a partial loss of catalytic activity. Polymerization conditions also play a pivotal role in determining the molecular weight of polyethylene. Hydrogen, being the most efficient chain transfer agent, can decrease the molecular weight to 9.68 × 104 g mol-1 at higher hydrogen concentrations ([H2] : [C2H4] = 0.83), and the s-POP-supported ethylene polymerization catalysts were observed to exhibit high sensitivity to hydrogen response. The effects of polymerization temperature, [Al] : [Ti] molar ratio, and ethylene pressure on ethylene polymerization were thoroughly investigated.

Strategies for enhancing the processability of UHMWPE

Four strategies to enhance the processability of UHMWPE are explored using heterogenised metallocene catalysts to produce polymers with decreased melt viscosity and excellent mechanical performance.

The genetics in polymers: Crystallization as a fingerprint of the molecular microstructure

Hidden details of the molecular structure of polymers can be revealed from the retro-analysis of the crystallization behavior. The way a polymer crystallizes and the selection of a specific polymorphic form upon crystallization contain all the information about the structure of macromolecules. The intriguing challenge is how to extract this information from the formed crystals. The key is the construction of a model and the availability of model systems of polymer crystallization based on the exploitation of the phenomena of polymorphism and isomorphism and on the understanding of how such phenomena are affected by the presence of microstructural defects. The explanatory case study of isotactic polypropylene (iPP) prepared with Ziegler-Natta catalysts is here described. iPP shows an intricate polymorphic behavior, which may be successfully exploited to build models of the crystallization behavior and reveal hidden details of the complex molecular structure dictated by the heterogenous multi-site Ziegler-Natta catalysts. A model of the crystallization behavior of iPP has been defined through deep analysis of the crystallization of iPP and its copolymers synthesized with soluble organometallic catalysts that produce a simple molecular structure with perfectly random distribution of defects. In these model systems the crystallization of the α and γ forms depend only on the average length of the regular propene sequences that, in turn, depends on the concentration of defects. A precise correlation between the amount of crystallized γ form and the average length of regular isotactic propene sequences is the basic of this model. This correlation can be used in more complex samples where the concentration of defects is not known or when the distribution of defects is not random as in Ziegler-Natta iPPs, as calibration curve to evaluate the length of regular propene sequences from the crystallization behavior by simply measuring the maximum amount of crystallized γ form. The retro-analysis of the crystallization behavior of iPP allows to disclose hidden aspects of the molecular structure of the extremely complex Ziegler-Natta polypropylene and provides evidence of the blocky structure of chains of iPP (and polyolefins in general) synthesized with Ziegler-Natta catalysts. This retro-analysis exploits the presence of polymorphism and is possible only for polymers that can crystallize in different polymorphic forms that exhibit thermodynamic stability and crystallization kinetics which depend on the molecular structure and, in particular, on the presence of defects.

Influence of the reaction conditions on the Ziegler-Natta catalyzed ethylene polymerization: Kinetics and properties of the resulting polymers

This work conducts an investigation into how the polymerization conditions affect the kinetics of ethylene homopolymerization and the properties of the final polyethylene using a commercially available Ziegler-Natta catalyst with the formula TiCl4/MgCl2. By employing a mathematical model, we estimated the apparent propagation (kp), activation (ka), and deactivation (kd) rate constants under different reaction conditions, including cocatalyst and catalyst concentration, hydrogen/ethylene ratio, and polymerization temperature. Additionally, we examined the properties of the resulting polyethylene products, such as particle size, molecular weight (Mw), melting temperature, and % crystallinity. We found that the trend of polymer particle size was similar to that of the propagation rate constant under the employed polymerization conditions. Our results indicated that parameters enhancing the polymerization rate also increased kp and reduced crystallinity. The quantitative rate constants and polymer characteristics reported in this study provide valuable insights for industrial polyethylene manufacturers, allowing them to fine-tune plant operation conditions and achieve precise control over polymer particle properties. Furthermore, Density Functional Theory (DFT) calculations provided additional insights into the polymerization process, particularly regarding the role of hydrogen as a chain transfer agent and the fundamental significance of MgCl2, emphasizing the need for a minimal-dimensional model to evaluate this role.

Stereoselectivity in Butadiene Polymerization Promoted by Using Ziegler–Natta Catalysts Based on (Anilidomethyl)pyridine Group (IV) Complexes

The stereoselective polymerization of conjugated dienes promoted by using transition metal complexes has attracted much interest in both industrial and academic environments for the relevance of polydienes as synthetic rubbers and for the challenging reaction mechanisms. Among the different transition metal complexes, those based on group IV have been demonstrated to be versatile and efficient catalysts. Titanium complexes are generally more active than zirconium complexes. A rare exception to this trend is represented by a series of Zr(IV) complexes supported by (anilidomethyl)pyridine ligands that, after activation by using Al(iBu2H)/MAO, were found to be highly active affording exclusively cis-1,4-polybutadiene. To rationalize this unexpected trend and to obtain more insights into the parameters that control the reactivity of group IV complexes, a theoretical investigation of the entire polymerization mechanism, employing density functional methods, was undertaken. In the framework of the widely accepted polymerization scheme, the different intermediates featuring h4 (both cis and trans) coordination of the monomer and h1 or h3 (syn or anti)allyl coordination of the growing chain were scrutinized. Subsequently, the effects of the metal center on the free-energy profiles of the elementary steps involved in the reaction were examined. The results presented herein aim to achieve a better knowledge of the influence of the metal on the polymerization rates and on the stereoselectivity of the reaction.