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A novel linear low‐density polyethylene containing H‐shape long‐chain‐branching structures (LCB‐LLDPE) is industrially synthesized with Ziegler‐Natta catalysts and gas‐phase polymerization process at the assistance of ω‐alkenylmethyldichlorosilane copolymerization‐hydrolysis chemistry. The incorporated LCB structures are characterized by NMR, SEC, and SAOS (small amplitude oscillatory shear) measurements. With a same‐sourced plain LLDPE as a comparison benchmark, the new LCB‐LLDPE is studied for its properties on various aspects, revealing, among others, significantly reinforced rheological properties, including enhanced shear‐thinning behavior, a significant strain‐hardening phenomenon in extensional flow, and substantially increased melt strength, as well as significantly improved optical properties, which all benefit its application in extrusion blow molding for thin‐film production. [ABSTRACT FROM AUTHOR]

The polypropylene (PP) synthesis process is crucial in the plastics industry, requiring precise control as it directly impacts the catalytic activity and the final product's performance. This study investigates the effects of trace amounts of four different mercaptans on the polymerization of propylene using a fourth-generation Ziegler–Natta (ZN) catalyst. Various concentrations of these mercaptans were tested, and results showed that their presence significantly reduced the melt flow index (MFI) of the final PP. The most notable MFI decrease occurred at 37.17 ppm of propyl mercaptan and 52.60 ppm of butyl mercaptan. Methyl and ethyl mercaptan also reduced the MFI at lower concentrations, indicating that mercaptans act as inhibitors by slowing down the polymerization process and reducing the fluidity of molten PP. The highest MFI increase was observed at lower concentrations of each mercaptan, suggesting that smaller molecular inhibitors require less concentration. This trend was also seen in the catalyst's productivity, where lower concentrations of methyl mercaptan reduced PP production more effectively than higher concentrations of butyl mercaptan. Fourier transform infrared spectroscopy (FTIR) identified interactions between the mercaptans and the ZN catalyst. Computational analysis further supported these findings, providing insights into the molecular interactions and suggesting possible inhibition mechanisms that could impact the final properties of polypropylene. [ABSTRACT FROM AUTHOR]

Acetylene and methylacetylene are impurities commonly found in the raw materials used for the production of polymers such as polypropylene and polyethylene. Experimental evidence indicates that both acetylene and methylacetylene can decrease the productivity of the Ziegler-Natta catalyst and alter the properties of the resulting polymer. However, there is still a lack of understanding regarding the mechanisms through which these substances affect this process. Therefore, elucidating these mechanisms is crucial to develop effective solutions to this problem. In this study, the inhibition mechanisms of the Ziegler-Natta catalyst by acetylene and methylacetylene are presented and compared with the incorporation of the first propylene monomer (chain initiation) to elucidate experimental effects. The Density Functional Theory (DFT) method was used, along with the B3LYP-D3 functional and the 6-311++G(d,p) basis set. The recorded adsorption energies were −11.10, −13.99, and −0.31 kcal mol−1, while the activation energies were 1.53, 2.83, and 28.36 kcal mol−1 for acetylene, methylacetylene, and propylene, respectively. The determined rate constants were 4.68 × 1011, 5.29 × 1011, and 2.3 × 10−8 M−1 s−1 for acetylene, methylacetylene, and propylene, respectively. Based on these values, it is concluded that inhibition reactions are more feasible than propylene insertion only if an ethylene molecule has not been previously adsorbed, as such an event reinforces propylene adsorption. [ABSTRACT FROM AUTHOR]

Propene polymerization kinetic profiles with a diether-based Ziegler–Natta MgCl2-supported catalyst were investigated in a stainless-steel batch reactor. The initial 10 min period characterizes various temperature levels with a constant volume of liquid propene. The lowest temperature level corresponds to the usual prepolymerization temperature (10 °C), and the highest level corresponds to the usual main polymerization temperature (70 °C). The effects of the starting temperature levels were evaluated through polymerization kinetic patterns computed namely from the second polymerization period carried out at 70 °C for the next 90 min. Based on the heat transfer data, the kinetic profiles were fitted to suitable semi-empirical equations derived from fundamental kinetic approaches using the first and second orders of the catalyst active sites decay. Both approaches adequately describe the dependence of the initial activities and deceleration constants on the temperature during the initial period. [ABSTRACT FROM AUTHOR]

The aim of this paper is to determine the effect of polymer density, correlated to the comonomer content, and nanosilica addition on the mechanical and Environmental Stress Cracking Resistance (ESCR) characteristics of high‐density polyethylene (HDPE). In this regard, five HDPE samples with similar Melt Flow Index (MFI) and molar mass but various densities were acquired from a petrochemical plant. Two polymerization reactors work in series and differ only in the amount of 1‐buene comonomer fed to the second reactor. To ascertain the microstructure of the studied samples, GPC and SSA (successive self‐nucleation and annealing) analyses were accomplished. All samples resulted having similar characteristics but slightly various SCB/1000 C=7.26–9.74 (SCB=Short Chain Branching). Consequently, meanwhile studied HDPEs reveal similar notched impact and stress at yield values, the tensile modulus, stress‐at‐break, and elongation‐at‐break tend to demonstrate different results with the SCB content. More significantly, ESCR characteristic varied considerably with SCB/1000 C extent, so that higher amount of SCB acknowledged advanced ESCR. Notably, blending HDPE sample containing higher amount of SCB/1000 C, with 3 wt.% of chemically modified nanosilica enhanced ESCR characteristic by 40 %. DFT (Density Functional Theory) calculations unveiled the role of the comonomer, quantitatively by binding energies and qualitatively by Non Covalent Interaction (NCI) plots. [ABSTRACT FROM AUTHOR]

This article commemorates the 50th anniversary of the passing of Karl Ziegler, a Nobel Prize-winning German chemist, by exploring his scientific journey and remarkable contributions. Ziegler's unwavering passion for science, unique thinking, and exceptional experimental skills formed the bedrock of his scientific endeavors. His research primarily focused on free radical compounds, polycyclic compounds, and organometallic compounds. The Ziegler-Natta catalyst, which he co-invented and named alongside Giulio Natta, had far-reaching implications for the global polyolefin industry, giving rise to a market worth billions of dollars. [ABSTRACT FROM AUTHOR]

Polypropylene is one of the most widely used synthetic resins, which is mainly synthesized with Ziegler-Natta catalysts. In this paper, the functionalized Ziegler-Natta catalyst is applied to prepare high-performance polypropylene. A new way to synthesize functionalized Ziegler-Natta catalysts is to dope with inorganic nanoparticles. The MgCl2/TiCl4/BMMF catalysts doped with halloysite nanotubes were prepared and applied to synthesize polypropylene containing less than 200ppm halloysite nanotubes. It is found that doping nanotubes in Ziegler-Natta catalyst has little impact on the structure, composition and activity of the catalyst, and polypropylene with high isotactic degree and molecular weight was synthesized with the functionalized Ziegler-Natta catalyst. Halloysite nanotubes are found to be dispersed in polypropylene in the form of individual nanotube, forming percolated network in the polymer melt effectively. Moreover, the polypropylene containing halloysite nanotubes exhibited better mechanical and thermal resistance properties as compared with conventional polypropylene, and the thermo-oxidative properties of which do not deteriorate as the introduction of nanotubes. This research provides a facile way to relieve the contradiction between the high activity of catalyst and high content of nanoparticles during the preparation of polyolefin nanocomposites by in-situ polymerization, and a new idea to prepare polyolefin nanocomposites by in-situ polymerization.

This report is on the characterization of active Ti center in heterogeneous Ziegler-Natta catalysts with Soft X-ray Emission Spectrometer (SXES). Since titanium in the catalyst has various chemical bonds, it is important to grasp the chemical bond state. The outermost shell electrons are very important for understanding the chemical bond state. SXES is the only method that can easily observe outermost shell electrons with current analytical instruments. Here, a co-milled solid of MgCl2, TiCl4, and Phthalate was used as a catalyst precursor, and three types of catalysts with significantly different catalytic activity levels were synthesized by changing the subsequent preparation process. The correlation between catalytic activity and the signal shape of Lα,β emission, which is the outermost shell electron of Ti in SXES analysis, was investigated. Lα,β emission was detected as broad signal. It could be observed that the high active catalyst had relatively strong signal intensity at the high energy side. The shape changes were also checked when the catalyst solids were treated by triethylaluminium. By this treatment, the relative intensity of the high energy side signal was further enhanced, suggesting that triethylaluminium treatment induced the elimination of inactive Ti from the catalyst solid. By comparing with the solid 13C-NMR analyses data of the Ziegler-Natta catalyst described in our previous report, the high energy side signal of Ti Lα,β in SXES results implies the relationship with the NMR results for carbonyl function.

In this paper, a series of novel trans‐1, 4‐polyisoprene/isotactic polybutene (TPI/iPB) in‐reactor blends were synthesized by isoprene and butene sequential two‐stage polymerization technology with spherical TiCl4/MgCl2 type Ziegler‐Natta catalyst. The components, structures, and properties of the as‐obtained TPI/iPB reactor blends were characterized by gel permeation chromatography, Fourier transform Infrared spectroscopy, and differential scanning calorimetry. The active trans‐1, 4‐polyisoprene (TPI) particles obtained in the initial isoprene polymerization by the Z‐N catalyst can be acted as microreactors to initiate butene polymerization subsequently. The TPI/iPB reactor blends with varied components were in situ synthesized within the reactor. The preparative‐temperature rising elution fractionation (p‐TREF) technique was used to fractionate the TPI/iPB reactor blends based on the elution temperature ranged from −40°C to 90°C. The weight distribution and microstructure of each fraction were investigated. The reactor blends are composed of crystallizable high trans‐1, 4‐uint polyisoprene obtained from the first‐stage isoprene polymerization, high isotactic polybutene obtained from the second‐stage butene polymerization and TPI‐b‐iPB block copolymer with different sequence structure obtained from the initial time of the second stage. This work is expected to propose the possible polymerizations of a‐olefins and conjugated dienes by using heterogeneous Ziegler‐Natta catalyst and provide a kind of novel rubber/plastic reactor blend materials. Highlights: The first synthesis of the trans‐1, 4‐polyisoprene/isotactic polybutene reactor blends.p‐TREF technique was used to analyze the composition of TPI/iPB reactor blends.Detailed structure characterization of the fractions including GPC and NMRTPI‐b‐iPB block copolymer can be obtained through the sequential polymerization.Rubber/plastic reactor blend materials were fabricated by the Z‐N catalyst. [ABSTRACT FROM AUTHOR]

This report is on the characterization of active Ti center in heterogeneous Ziegler-Natta catalysts by Soft X-ray Emission Spectrometry (SXES). Since titanium in the catalyst has various chemical bonds, it is important to grasp the chemical bond state. The outermost shell electrons are very important for understanding the chemical bond state. SXES is the only method that can easily observe outermost shell electrons with current analytical instruments. Here, a co-milled solid of MgCl2, TiCl4, and phthalate was used as a catalyst precursor, and three types of catalysts with significantly different catalytic activity levels were synthesized by changing the subsequent preparation process. The correlation between catalytic activity and the signal shape of Lα,β emission, which is the outermost shell electron of Ti in SXES analysis, was investigated. Lα,β emission was detected as broad signal. It could be observed that the high active catalyst had a relatively strong signal intensity at the high energy side. The shape changes were also checked when the catalyst solids were treated by triethylaluminum. By this treatment, the relative intensity of the high energy side signal enhanced further, suggesting that the triethylaluminum treatment induced the elimination of inactive Ti from the catalyst solid. By comparing with the solid 13C-NMR analyses data of the Ziegler-Natta catalyst described in our previous report, the high energy side signal of Ti Lα,β in SXES results implies the relationship with the NMR results for carbonyl function. [ABSTRACT FROM AUTHOR]

MgCl2/2-Ethylhexanol/TiCl4system was used to synthesize spherical Ziegler-Natta catalyst for ethylene polymerization, and the composite internal electron donor was added in the synthesis process:nhexyl acetate/diisobutyl phthalate was compared with tetraethoxysilane, ethyl acetate and diisobutyl phthalate as electron donors, respectively.The catalysts and polymers containing different internal electron donors were analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), and the catalytic performance of the catalysts was evaluated by ethylene polymerization.The results showed that under the conditions of temperature 80℃, pressure0.5 MPa and time 2 h, the catalytic activity of the catalyst containing complex internal electron donornhexyl acetate/diisobutyl phthalate was higher than that of other single internal electron donor catalysts, and the catalytic activity was 1.24×105g PE/(molTi·h). [ABSTRACT FROM AUTHOR]

MgCl2·nEtOH adducts play a major role in the industrial production of polyethylenes. Their chemical dealcoholation, usually accomplished during the catalyst synthesis step, has had a pronounced impact on the microstructure of the final Ziegler–Natta pre‐catalysts and the properties of the resulting polymers. Due to the industrial and academic importance of this issue, different aluminum‐based compounds including triethylaluminum (TEAL), triisobutylaluminum (TIBA), and ethylaluminumdichloride (EADC) were used in this research in the chemical dealcoholation of a MgCl2·1.5EtOH adduct, to provide the target catalysts. According to the analytical results, the catalysts synthesized using aluminum compounds (especially TEAL and EADC) generally had a more fractured structure, a smaller particle size and a vast surface area. Aluminum precursors bind to the catalyst structure together with TiCl4, which is manifested from their higher adsorption energies obtained by DFT calculations, and the presence of Al atom in the elemental analysis. Varying the chemical structure and physical properties of the catalysts, established using Al compounds, caused significant variation in the ethylene polymerization kinetic curves, their related rate constants, and the flow characteristic of the final polymers. The overall results outstandingly affirm that by appropriate choice of the Lewis acid compound, during the chemical dealcoholation of the adduct, various Ziegler–Natta catalysts can be achieved for different polyethylene grades. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of different prepared magnesium sources including MgCl2 (ZN-THF), metallic magnesium powder (ZN-O), and MGE (ZN-MGE) as the support of titanium-based Ziegler-Natta catalysts on behaviors of gas-phase ethylene/1-hexene copolymerization was investigated. These catalysts reacted with TEA presented higher catalytic activity than using TnOA. This is due to TEA had higher reducing power. Moreover, it revealed that ZN-MGE exhibited the highest activity among other catalysts because ZN-MGE had the highest distribution of titanium contents measured by EDX, and then generated more active sites. The average particle sizes of these catalysts were around 35 µm, which was suitable for commercial application. Considering copolymer size, the size of EH-ZN-O-TEA and EH-ZN-MGE-TnOA (ca. 420 µm) displayed the largest particle size. The large size of EH-ZN-MGE-TnOA was expected due to the agglomeration and steric hindrance of the catalyst reacted with TnOA. For the particle size distribution, only EH-ZN-O-TEA showed the bimodal distribution meaning that both fragmentation and no fragmentation occurred. Other copolymers showed positive-skewed distribution. Typically, the morphologies of copolymer were spheroidal lump without fine particles. The roles of comonomer content on thermal behaviors were presented by melting temperature, C7-soluble content, and crystallinity. It was found that although all catalysts with TEA exhibited higher activity than TnOA, the use of TnOA perhaps tended to facilitate the comonomer insertion. It revealed that steric hindrance of TnOA cocatalyst may retard the copolymer chain attachment. As the result, the comonomer insertion of EH-ZN-MGE was the highest among other catalysts.

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. [ABSTRACT FROM AUTHOR]

The data scientific approach has become an indispensable tool for capturing structure–performance relationships in complex systems, where the quantity and quality of data play a crucial role. In heterogeneous olefin polymerization research, the exhaustive and multi-step nature of Ziegler-Natta catalyst synthesis has long posed a bottleneck in synthetic throughput and data generation. In this contribution, a custom-designed 12-parallel reactor system and a catalyst synthesis protocol were developed to achieve the parallel synthesis of a magnesium ethoxide-based Ziegler-Natta catalyst. The established system, featuring a miniature reaction vessel with magnetically suspended stirring, allows for over a tenfold reduction in synthetic scale while ensuring the consistency and reliability of the synthesis. We demonstrate that the established protocol is highly efficient for the generation of a catalyst library with diverse compositions and physical features, holding promise as a foundation for the data-driven establishment of the structure–performance relationship in heterogeneous olefin polymerization catalysis. [ABSTRACT FROM AUTHOR]

Ethylene/1‐hexene copolymerization with two MgCl2‐supported Ziegler‐Natta catalysts containing no internal electron donor or diethylphthalate (DEP) is conducted for different polymerization time. Effects of DEP on active center distribution are studied by fractionating each copolymer sample into boiling n‐heptane soluble (C7‐sol) and insoluble (C7‐ins) fractions, and counting the number of active centers in the copolymer fractions. The main effect of introducing DEP in the catalyst are reduction in the Ti content and significant increase in the proportion of active centers producing C7‐ins fraction. The propagation rate constants of ethylene insertion (kpE) and 1‐hexene insertion (kpH) are respectively estimated by linear fitting/extrapolating the change of apparent propagation rate constants (kpi)a with polymer yield according to a simplified multi‐grain particle model. In both catalysts, kpE in the C7‐ins fraction is 9–12 times larger than that in the C7‐sol fraction, and kpH in the C7‐ins fraction is 3–4 times larger than that in the C7‐sol fraction. The two groups of active centers have distinctly different catalytic properties. Introducing DEP reduced the kpE and kpH values and the extent of diffusion limitation. In summary, addition of electron donor in MgCl2‐supported Z‐N catalyst significantly changed the active center distribution and catalytic properties of its two groups of active centers. [ABSTRACT FROM AUTHOR]

ω‐Alkenyltrimethylsilanes of different alkenyl moieties, i.e., 3‐butenyltrimethylsilane, 5‐hexenyltrimethylsilane, and 7‐octenyltrimethylsilane, are used as model compounds to study the alkenyl length effect in copolymerization of ethylene with steric‐hindered tri‐substituted silane‐functionalized α‐olefins over MgCl2/TiCl4 catalysts. The experimental results reveal that 3‐butenyltrimethylsilane tops the three α‐olefins in incorporation rate into PE while 7‐octenyltrimethylsilane is slightly better than 5‐hexenyltrimethylsilane. The coordination‐insertion events for different ω‐alkenyltrimethylsilanes are investigated by DFT simulation. The results suggest that the three ω‐alkenyltrimethylsilanes encounter similar energy barriers during insertion, with similar repulsive interactions between the bulky trimethylsilane substituent and growing PE chain found in the energy decomposition of transition state configuration. However, complexation abilities at the Ti active site for the three ω‐alkenyltrimethylsilanes follow the order of 3‐butenyltrimethylsilane > 5‐hexenyltrimethylsilane > 7‐octenyltrimethylsilane, in line with their molecular compactness, which are deemed to be where the alkenyl length effect originates in the ω‐alkenyltrimethylsilane/ethylene copolymerization. [ABSTRACT FROM AUTHOR]

In this article, we present the influence of substituents with different electron-donating (ED) powers on the coordination properties of bis(benzoyloxy)dimethylsilane (BDMS) on the MgCl2 support of Ziegler–Natta (ZN) catalysts through molecular simulation of different adsorption adducts. Thermodynamically, the most favourable adsorption structure was found with the diaminoborane substituent in a bridging mode on the (110) crystalline facet, representing a 37.63% increase at PBEh/TZVP in the adsorption strength of the original silyl ester. Generally, the higher the ED strength of the substituent, the higher the exergonicity of donor coordination. All of the new donors except those containing the nitro and formyl groups are preferably chemisorbed on the (110) surface. While the nitro, formyl, vinyl, and hydroxyl substitutions deteriorated the isotacticity of the polymer, a diaminoborane group was predicted to enhance the isotactic index by 306% relative to the original donor. Particularly, nitrophenyl could improve the isotactic index by 69% while its complexation remained in the thermodynamically controlled regime. Overall, the present DFT study demonstrated how a systematic exploration of substituents over a wide range of ED power can help in the design of new Lewis base donors for ZN catalysis. [ABSTRACT FROM AUTHOR]

This research study examined how the use of dimethylformamide (DMF) as an inhibitor affects the propylene polymerization process when using a Ziegler–Natta catalyst. Several experiments were carried out using TiCl4/MgCl2 as a catalyst, aluminum trialkyl as a cocatalyst, and different amounts of DMF. Then, we analyzed how DMF influences other aspects of the process, such as catalyst activity, molecular weight, and the number of branches in the polymer chains obtained, using experimental and computational methods. The results revealed that as the DMF/Ti ratio increases, the catalyst activity decreases. From a concentration of 5.11 ppm of DMF, a decrease in catalyst activity was observed, ranging from 45 TM/Kg to 44 TM/Kg. When the DMF concentration was increased to 40.23 ppm, the catalyst activity decreased to 43 TM/Kg, and with 75.32 ppm, it dropped even further to 39 TM/Kg. The highest concentration of DMF evaluated, 89.92 ppm, resulted in a catalyst productivity of 36.5 TM/Kg and lost productivity of 22%. In addition, significant changes in the polymer's melt flow index (MFI) were noted as the DMF concentration increased. When 89.92 ppm of DMF was added, the MFI loss was 75%, indicating a higher flowability of the polymer. In this study, it was found that dimethylformamide (DMF) exhibits a strong affinity for the titanium center of a Ziegler–Natta (ZN) catalyst, with an adsorption energy (Ead) of approximately −46.157 kcal/mol, indicating a robust interaction. This affinity is significantly higher compared to propylene, which has an Ead of approximately −5.2 kcal/mol. The study also revealed that the energy gap between the highest occupied molecular orbital (HOMO) of DMF and the lowest unoccupied molecular orbital (SOMO) of the Ziegler–Natta (ZN) catalyst is energetically favorable, with a value of approximately 0.311 eV. [ABSTRACT FROM AUTHOR]

In this experimental–theoretical study, the effect of furan on Ziegler–Natta catalyst productivity, melt flow index (MFI), and mechanical properties of polypropylene were investigated. Through the analysis of the global and local reactivity of the reagents, it was determined that the furan acts as an electron donor. In contrast, the titanium of the ZN catalyst acts as an electron acceptor. It is postulated that this difference in reactivity could lead to forming a furan–titanium complex, which blocks the catalyst's active sites and reduces its efficiency for propylene polymerization. Theoretical results showed a high adsorption affinity of furan to the active site of the Ti catalyst, indicating that furan tends to bind strongly to the catalyst, thus blocking the active sites and decreasing the availability for propylene polymerization. The experimental data revealed that the presence of furan significantly reduced the productivity of the ZN catalyst by 10, 20, and 41% for concentrations of 6, 12.23, and 25.03 ppm furan, respectively. In addition, a proportional relationship was observed between the furan concentration and the MFI melt index of the polymer, where the higher the furan concentration, the higher the MFI. Likewise, the presence of furan negatively affected the mechanical properties of polypropylene, especially the impact Izod value, with percentage decreases of 9, 18, and 22% for concentrations of 6, 12.23, and 25.03 ppm furan, respectively. [ABSTRACT FROM AUTHOR]

The Ti immobilization process is directly modulated by the THF migration, which reduces the aggregation of TiCl 4 and enhances the formation of active species. [Display omitted] • Formation mechanism of the active species are traced by the in-situ spectra. • Active species distribution of the Ziegler-Natta catalyst is modulated by the THF migration. • The polyethylene with a narrow distribution is synthesized with a high activity owing to the synchronous migration of THF and immobilization of TiCl 4. Manipulating the interplay between electron donor and catalytic species is a major approach of optimizing Ziegler-Natta catalysts. To this end, it is essential to reveal the correlation between the involved dynamic processes. In this work, a greatly enhanced mobility of the internal donor tetrahydrofuran (THF) is realized even at room temperature in the MgCl 2 substrate modified with MgCl functionalized polyhedral oligomeric silsesquioxane (POSS-MgCl). A series of spectroscopic characterizations evidence that, thanks to the high mobility of THF, the immobilization of catalytic Ti species and the migration of THF occurs synchronously and leads to a nearly homogenous distribution of Ti sites. In addition, the incorporation of POSS-MgCl promotes the formation of 4-coordinated Mg sites in the substrate. The modified Ziegler-Natta catalyst shows the remarkable performance toward ethylene polymerization, featured by the high catalytic activity (21.6 × 106 g PE(mol Ti·h)−1) as well as a narrow polydiversity index (3.1) of the synthesized polyethylene. Based on these results, we propose that the Ti immobilization process is directly modulated by the THF migration in this system, which reduces the aggregation of TiCl 4 and enhances the formation of active species. [ABSTRACT FROM AUTHOR]

In olefin polymerization with MgCl2‐supported Ziegler–Natta (Z–N) catalysts, the apparent propagation rate constant (kp)a calculated by Rp = (kp)a [C*] CMe (CMe is equilibrium monomer concentration in the reaction system) declines with reaction time for gradually developed monomer diffusion limitation in the polymer/catalyst particles. In this work, a simplified multi‐grain particle model was proposed to build correlation between (kp)a and other kinetic parameters that can be determined experimentally. Rate profiles of propylene polymerization and ethylene‐1‐hexene copolymerization by three MgCl2‐supported Z–N catalysts were determined, and the (kp)a data was calculated using [C*] determined by quench‐labelling the propagation chains with acyl chloride. Decline of (kp)a in each polymerization process was precisely fitted by the linear correlation between lg(kp)a and [(ρcatmp)/(ρpmcat) + 1]1/3 developed on the particle model. Real propagation rate constant (kp) was estimated by extrapolating the fitting line to the starting point of polymerization, where no concentration gradient exists. According to the particle model, the slope of the lg(kp)a versus [(ρcatmp)/(ρpmcat) + 1]1/3 line (lgd) represents the degree of monomer diffusion limitation. Variations of parameter d found in the studied reaction systems can be reasonably explained based on the knowledge of olefin diffusion in the polymer phase. [ABSTRACT FROM AUTHOR]

Three ω‐alkenyltrimethylsilanes of different alkenyl moieties, i.e., 3‐butenyltrimethylsilane, 5‐hexenyltrimethylsilane, and 7‐octenyltrimethylsilane, are copolymerized with propylene over a heterogeneous Ziegler‐Natta catalyst. The experimental results reveal that, at odds with what the molecular volumes will foretell, 5‐hexenyltrimethylsilane top the three ω‐alkenyltrimethylsilanes in incorporation rate into PP while 3‐butenyltrimethylsilane becomes the most sluggish of the three. This comonomer incorporation rate order is in line with that of ω‐alkenylmethyldichlorosilanes in copolymerization with propylene‐synthesizing long‐chain‐branched PP (LCB‐PP), pointing to a peculiar alkenyl length effect on comonomer incorporation rate for these comonomers. DFT simulation is then applied to seek energetic basis in coordination‐insertion for such an effect. It is revealed that complexation abilities of the three ω‐alkenyltrimethylsilanes decrease in the following order: 3‐butenyltrimethylsilane > 5‐hexenyltrimethylsilane > 7‐octenyltrimethylsilane, in line with their molecular sizes. However, the insertion energy barriers increase in the order of: 5‐hexenyltrimethylsilane < 7‐octenyltrimethylsilane < 3‐butenyltrimethylsilane. The repulsive interaction between the bulky trimethylsilane functionality of ω‐alkenyltrimethylsilanes and growing PP chain is found to contribute significantly to the insertion energy barrier, which grows disproportionally large with 3‐butenyltrimethylsilane. The current discovery will be conducive to understanding the more complex ω‐alkenylmethyldichlorosilane/propylene copolymerization that synthesizes the industrially important LCB‐PP. [ABSTRACT FROM AUTHOR]

The presence of impurities such as H2S, thiols, ketones, and permanent gases in propylene of fossil origin and their use in the polypropylene production process affect the efficiency of the synthesis and the mechanical properties of the polymer and generate millions of losses worldwide. This creates an urgent need to know the families of inhibitors and their concentration levels. This article uses ethylene green to synthesize an ethylene–propylene copolymer. It describes the impact of trace impurities of furan in ethylene green and how this furan influences the loss of properties such as thermal and mechanical properties of the random copolymer. For the development of the investigation, 12 runs were carried out, each in triplicate. The results show an evident influence of furan on the productivity of the Ziegler–Natta catalyst (ZN); productivity losses of 10, 20, and 41% were obtained for the copolymers synthesized with ethylene rich in 6, 12, and 25 ppm of furan, respectively. PP0 (without furan) did not present losses. Likewise, as the concentration of furan increased, it was observed that the melt flow index (MFI), thermal (TGA), and mechanical properties (tensile, bending, and impact) decreased significantly. Therefore, it can be affirmed that furan should be a substance to be controlled in the purification processes of green ethylene. [ABSTRACT FROM AUTHOR]

A robust immobilization strategy is proposed by the self-assembly of POSS and TiCl 4 molecules, where a flexible double-Ti structure shows the most reduced energy barrier for ethylene insertion. [Display omitted] • A highly active molecular catalyst toward ethylene polymerization was synthesized according to the self-assembly of POSS and TiCl 4. • A flexible double-Ti structure coordinated to Si-O-Si shows the most reduced energy barrier for ethylene insertion. • Catalytic nanoparticles show robust resistance to H 2 , enhanced incorporation of comonomer, and reduced entanglements of the synthesized polymer. Heterogeneous catalysis plays a crucial role in industrial olefin polymerization. Mechanistic understanding and optimization of Ziegler-Natta (ZN) catalyst are limited by the considerable complexity resulting from the multiple ingredients and complicated structures. Re-designing ZN catalytic systems with reduced complexity and adequate performance is of great interest. Here, we show that self-assembled polyhedral oligomeric silsesquioxane (POSS)@TiCl 4 nanoparticles can effectively immobilize TiCl 4 molecules in n -heptane solution, achieving the exceptional utilization of active centres. This uncomplicated system exhibits heterogeneous-like catalytic performance in ethylene polymerization, featured by high activities, fouling-free polymerization and a series of desirable properties of the nascent polymers such as reduced entanglement and spherical morphology. In addition, these catalytic nanoparticles show robust resistance to H 2 , and enhanced incorporation of comonomer towards ethylene/1-hexene copolymerization. By using DFT calculations the possible structures of the Ti active centres are proposed, of which a flexible double-Ti structure coordinated to Si-O-Si shows the most reduced energy barrier for ethylene insertion. [ABSTRACT FROM AUTHOR]

The creep resistance of polymer determines the dimensional stability of product under stress. The isotactic polybutene-1 (iPB) with outstanding high-temperature creep resistance and stress-crack resistance is applied widely in the field of hot-water pipes. Although the chain information including weight-average molecular weight (Mw) and aggregate structures of isotactic polybutene-1 (iPB) influence the creep resistance, the crucial factor affecting the creep behavior greatly is unclear. In this work, a series PB samples with varied Mw, isotacticity and configurational sequence were synthesized and characterized based on Gel Permeation Chromatography (GPC), solvent fractionation and Nuclear Magnetic Resonance Spectroscopy (NMR). The Differential Scanning Calorimetry (DSC), Wide-angle X-ray diffraction (WAXD) and Small angle X-ray scattering (SAXS) were used to characterize the aggregation structures of PB samples. The stress-strain behaviors and 95 °C creep deformation of these PB samples were testes by tensile test and Dynamic Mechanical Analysis (DMA), respectively. It was found that these PB samples showed different chain microstructures like 88–99 wt% high isotactic PB (HiPB) fractions, 90–97.6 mol% tetra-meso placements (mmmm) in HiPB fraction, and 50 × 104-160 × 104 Mw. Increasing the molecular weight, isotacticity or configurational sequence mmmm enhanced the creep resistance of PB, while mmmm configurational sequence played more important role in creep resistance of PB through adjusting the aggregation structure (crystalline domains) of the final product greatly. Exploring the influencing factors of creep resistance provided guidance for the synthesis of high-performance PB for high-temperature pipe application.

Propylene polymerization using magnesium dichloride (MgCl2) supported Ziegler–Natta (Z–N) system is a robust and preferred catalytic process for producing polypropylene (PP) grades. Herein, synthesis of polypropylene products is reported using MgCl2 supported multidentate (3,3,3′,3′‐tetramethyl‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobiindane‐5,5′,6,6′‐tetracarbonate) Z–N pre‐catalyst. The catalyst performance evaluation over propylene polymerization found that multidentate Z–N pre‐catalyst has better hydrogen response with controlled isotacticity of PP products as compared to conventional bidentate Z–N pre‐catalysts. Melt rheology analysis showed higher loss modulus and storage modulus for ultra‐high molecular weight isotactic polypropylene (UHMWiPP) as compared to PP resins with medium molecular weight. Further, GPC analysis reveal medium to broad unimodal molecular weight distribution (MWD) of PP products produced with multidentate Z–N pre‐catalyst system. [ABSTRACT FROM AUTHOR]

Porous organic polymers (POPs) have attracted much attention in numerous areas, including catalysis, adsorption and separation. Herein, POP supported Ziegler–Natta catalysts were designed for preparation of isotactic polypropylene (iPP). The POPs-based Ziegler–Natta catalysts exhibited the characteristic of broad molecular weight distribution (MWD > 11) with or without adding an extra internal electron donor. The added internal electron donor 3-methyl-5-tert-butyl-1,2-phenylene dibenzoate (ID-2) used in cat-2 showed good propylene polymerization activity of 15.3 × 106 g·PP/mol·Ti·h, high stereoregularity with 98.2% of isotacticity index and broad molecular weight distribution (MWD) of 12.3. Compared to the MgCl2-supported Ziegler–Natta catalysts (cat-4) with the same ID-2, cat-2 showed higher chain stereoregularity for propylene polymerization. As seen in the TREF results, the elution peak of PP-2 (124.0 °C, 91.7%) is 1.5 °C higher than the isotactic fraction from PP-4 (122.5 °C, 87.2%), and even 1.2 °C higher than PP-5 prepared from ID-3 with the characteristics of high stereoregularity. Moreover, the pentad methyl sequence mmmm of PP-2 (93.0%) from cat-2 is 0.5% higher than that of PP-4 from cat-4. XPS analysis revealed that the minute difference in binding energy of Ti, Mg, C and O atoms exist between the inorganic MgCl2 and the organic polymer based Z–N catalysts. The plausible interaction mechanism of active sites of Mg and Ti with the functional groups in the POP support and the added ID was proposed, which could be explained by their high stereoregularity and the broad molecular weight distribution of the POP-based Z–N catalysts. [ABSTRACT FROM AUTHOR]

A set of MgCl2.EtOH adducts was synthesized by employing two different weight fractions of span 80 (0.5, and 1.0 wt.%) as an emulsifier during adduct preparation step by melt quenching method. Spherical morphology of the prepared adducts was explored using scanning electron microscopy. Further characterization results revealed that emulsifier containing adducts had similar crystalline structure, higher ethanol content and smaller particle sizes. Prepared adduct samples were employed in TiCl4/MgCl2 (Ziegler–Natta) catalysts synthesis which subsequently tested in slurry-phase ethylene polymerization in the presence of triethylaluminium as a cocatalyst. The ethylene polymerization results disclosed that, using emulsifier caused to high active catalyst samples in comparison with emulsifier-free one, where catalyst activity increased up to 40% by using 1.0 wt.% of emulsifier. And as a significant achievement, molecular weight results showed that, synthesized catalysts in the presence of emulsifier led to the production of ultra-high molecular weight poly ethylene with Mv > 1.5 × 106 g/mol at low ethylene pressure of only 2 bar. The production of ultra-high molecular weight poly ethylene together with small particle size feature make the catalyst containing 1 wt.% emulsifier as a good candidate for industrialization step through slurry-phase plants. [ABSTRACT FROM AUTHOR]

Ziegler–Natta (ZN) catalyzed polymerizations have been used for the production of a wide variety of polyolefin with different characteristics and various applications such as polyethylene and polypropylene. In such polymerization processes, different parameters such as polymerization temperature, monomer pressure, and [Al]/[Ti] molar ratio play an important role in conducting a successful polymerization with desired productivity and final product properties. This paper aims to investigate the individual and simultaneous effects of these parameters on the catalyst activity, polymerization yield, and resultant polymer properties. For this purpose, a new three-metallic high-performance ZN catalyst was synthesized for applying in the ethylene polymerization. Response surface methodology (RSM) and an N = 15 Box-Benkhen design were used to analyze the catalyst activity and polymerization yield. The result revealed that catalyst activity and polymerization yield increase by increasing the polymerization pressure and [Al]/[Ti] ratio while increasing polymerization temperature decrease both above-mentioned responses. Optimal polymerization parameters suggested by the program are applied to the polymerization process for obtaining higher catalyst activity and polymerization yield. Kinetic behavior of catalyst also has been investigated through polymerization course. In the final part of the present work, comprehensive characterization of obtained polymer in terms of thermo-physical and mechanical properties have been conducted. The result revealed that the obtained polymer is an ultrahigh molecular weight polyethylene. [ABSTRACT FROM AUTHOR]

Ziegler-Natta catalyst for propylene polymerization, which TiCl4 and di-alkyl phthalate were supported on MgCl2, was analyzed by solid state 13C NMR. It was confirmed that the spin-lattice relaxation time (“relaxation time” hereafter) of carbonyl group in phthalate was shortened with increasing measurement temperature as a general manner because of the enhancing of molecular mobility at high temperature. The degree of the relaxation period reduction with temperature was influenced by the alkyl group size in phthalate molecule; the larger alkyl group showed a greater shorting of the relaxation period. A short relaxation time should suggest a weak interaction between the phthalate molecule and the MgCl2 support surface. The change in catalytic performance was discussed by the active site formation mechanism involving the phthalate removal step.

The gas‐phase ethylene polymerizations with SiO2‐supported Ziegler–Natta (ZN) catalyst at early moments of reaction is modeled. The experimental data used in this work show that at initial stages of the polymerization there is a sharp reduction in the reaction rate and a sharp rise in molecular weight. In the modeling, multi‐active sites assumption and diffusion limitations inside the particle are studied. Energy balance to calculate the temperature at early moment is applied. Kinetic model including initiation, propagation, chain transfers and active site deactivation steps are used to predict the reaction rate and molecular weights. Polymeric flow model (PFM) is applied for single particle model (SPM). The results show two distinct regions. First region with sharp gradient for reaction rate and molecular weights and then, shortly there is a smooth region in which the changes in rate and molecular weights are slow. To fit this sharp gradient followed by a nearly steady state behavior two types of active sites are necessary. A group of highly active sites which deactivated soon and the active sites with lower activity and relatively long‐lasting. [ABSTRACT FROM AUTHOR]

Chemical 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. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) is one of the most widely used commodity plastic materials worldwide in terms of the production and its consumption. At commercial scale, PP is produced in various grades like homopolymer and copolymer (random and impact) by the polymerization of propylene and mixture of propylene-ethylene monomers using Ziegler–Natta catalysts and alkyl aluminum as co-catalysts. The present study deals with the colored lump formation of polypropylene random copolymer (PPCP) during storage at large scale and its probable route cause analysis for the lump formation. The lump samples were collected and characterized using FTIR, TGA, DSC and molecular weight determination and compared with pure PPCP. FTIR data show all the signature peaks of PPCP with additional > C=O stretching near 1720 cm−1 in colored lump sample, TG analysis revealed degradation of PPCP polymer and formation of volatile organic compounds in the temperature range 200–250 °C, the DSC analysis of the colored lump and pure PPCP showed that the melting peak was broader for colored lump of PPCP (i.e., PPCP_Y) which is an indicative that polymer molecules were having different chain length and the molecular weight analysis showed that the colored sample was having very low molecular weight with some bimodal character as compared to pure polymer. Based on these data and observations, the possible reason for the colored lump formation was also discussed. [ABSTRACT FROM AUTHOR]

The sustainability of consumer materials, such as plastics, belongs to the most important aspect of eco‐efficiency analyses. Besides mechanical recycling, chemical recycling represents an interesting waste management pathway. In theory, this technique does not rely on single‐grade feedstock to maintain product quality. However, cross‐contamination of feedstocks potentially leads to above‐specification impurities in obtained pyrolysis oils. This study investigates the potential downstream poisoning of a fourth‐generation Ziegler‐Natta catalyst, using selected model poisons at high (worst‐case) concentrations. With experimental and computational analysis, economic feasibility factors such as catalyst activity and microstructural properties are evaluated during the synthesis of high‐density polyethylene (HDPE) and linear low‐density polyethylene (LLDPE). Noticeable effects on the catalyst activity can be observed when the poison interacts with the co‐catalyst, whereas a lower impact is observed for interactions with the activated catalyst‐co‐catalyst complex. Molecular weight distribution (MWD) and comonomer composition distribution (CCD) modeling highlighted marginal to no polymer property changes caused by contaminants. Combined with the applicability of pyrolysis post‐treatments, these observations show that chemical recycling can be a promising technique for post‐consumer plastic waste treatment. [ABSTRACT FROM AUTHOR]

A three-metallic high-performance heterogeneous Ziegler–Natta-type catalyst for polymerization of ethylene was synthesized using titanium tetrachloride as the active center, magnesium ethoxide as the support, and ethylaluminum sesquichloride (EASC) as a chlorinating agent. The prepared catalyst was characterized by FTIR, XRD, TGA, and BET methods. FTIR and XRD patterns evidenced that Mg(OEt)2 was fully converted to MgCl2 during catalyst synthesis. The specific surface area (SSA) of the synthesized catalyst was calculated to be 44.83 m2/g. Morphological studies by the SEM technique demonstrated that the obtained catalyst had the particles with a disordered pattern. Elemental analysis of the catalyst, performed by X-ray fluorescence (XRF), titration, and UV–Vis spectroscopy techniques, confirmed a large amount of titanium on the support's bed. Polymerization of ethylene was conducted by employing synthesized catalyst using triethylaluminum as cocatalyst. In the polymerization reaction, the synthesized tri-metallic catalyst exhibited high activity of 9.50 kg PE.g Cat−1. h−1. In the last part, to explore the possible interaction of EASC with catalytic reagents, density functional theory (DFT) simulation was conducted. [ABSTRACT FROM AUTHOR]

Gas-phase polymerization of propylene via 4th generation Ziegler-Natta (ZN) catalysts was studied and optimized using intelligent data-based methods. The effect of co-catalyst (triethylaluminium (TEA)) and external donor (ED) compositions on the activity and PP-isotacticity for two commercial MgCl 2 /TiCl 4 /phthalate(ID)/TEA/silane(ED) catalyst systems with different Ti-contents were investigated using design-of-experiment (DOE) combined with response-surface-methodology (RSM). Sobol's sensitivity analysis was employed to determine the quantitative impact of catalyst compositions on the target variables. Both catalysts performance was optimized via multi-objective genetic algorithm (GA) to maximize the activity and PP-isotacticity. Results revealed that the activity and PP-isotacticity for both catalysts will be enhanced at low co-catalyst and high ED amounts, respectively. Increasing the ED improved the activity of low-Ti catalyst, whereas it reduced the activity of high-Ti one. Sensitivity results for both catalysts depicted the comparable influence of co-catalyst and ED on the activity and the strong influence of ED on PP-isotacticity. GA optimization offered the activity of 3.7 – 4.65 gPP/mgCat and PP-isotacticity of 95.8 – 97.5 % for low-Ti catalyst at the optimal TEA/Catalyst = 7 – 7.2 and TEA/ED = 6.0 – 7.2 and the activity of 3.9 – 4.7 gPP/mgCat and PP-isotacticity of 93 % for the high-Ti one at the optimal TEA/Catalyst = 7 – 11.2 and TEA/ED = 12. [Display omitted] • Gas-phase polymerization of propylene via Ziegler-Natta catalysts was intensified. • Effect of co-catalyst and external donor on polymerization performance was studied. • Co-catalyst and external donor showed a comparable impact on catalyst activity. • PP-isotacticity was strongly sensitive to the variations of the external donor. • Genetic algorithm was used to maximize both catalyst activity and PP-isotacticity. [ABSTRACT FROM AUTHOR]

In this study, the relationship between the characteristics of catalysts and polymerization conditions with catalyst behavior and polymer properties in the ethylene/α-olefin (co)polymerization using Ziegler–Natta catalyst (TiCl4/MgCl2 based) is investigated. The results showed that the differences in the characteristics of a catalyst such as particle size,surface area, porosity and particle size distribution of catalyst, and different polymerization conditions such as the presence of comonomer, can be a very important factors in determining catalyst behavior and product properties. For this purpose, two catalysts (cat1, cat2) TiCl4/MgCl2 based have been used and ethylene/α-olefin(co)polymerization was performed in slurry phase. Comparison results of DSC copolymers produced using both cat1 and cat2 showed that copolymerization in the presence of comonomers using cat2 catalyst shows better activity and comonomer incorporation than cat1 due to higher titanium content in the surface, larger surface area, possibility of access to more active centers. Besides that results of RMS showed that the presence of comonomer 1-butene and 1-hexane in the copolymers due to the increase in melt flow index, molecular weight has decreased and as a result, the storage and loss modulus has decreased. The inverse method with Van Ruymbeke model showed that the presence of 1-butaene comonomer in copolymerization with cat1 caused a change in the distribution of active catalytic centers and narrowed the molecular weight distribution. [ABSTRACT FROM AUTHOR]

Understanding the nature of the active species of the TiCl4/MgCl2 Ziegler–Natta catalyst is special important and challenge. In this work, the pre-treated TiCl4/MgCl2 pre-catalyst by heptane washing (H-Cat) and AlR3 activation (Al-Cat) were prepared and analyzed and then used to conduct butadiene (Bd)-isoprene (Ip) copolymerizations. It was proved that the adsorbed Al compounds on the Al-Cat surfaces after suffering heptane washing increased with the increase in the concentration of alkylaluminium in the pre-catalyst activation process, indicating the stable absorption of Al compounds on the active species and then influencing the catalytic behavior of the active species. Correlated the titanium oxidation state and the catalytic activity, Ti3+ species were more likely the active species for Bd-Ip copolymerization. Ti3+with adsorption of AlR2Cl on Mg adjacent to the Ti species showed reduced activity and produced polymers with high trans-1,4-configuration and relatively high molecular weight (Mw). This study is anxious to provide further understanding on the mechanism of conjugated diene polymerization catalyzed by heterogeneous Ziegler–Natta catalysts. The increase in alkylaluminium concentration during the pre-catalyst activation process changed the chemical surroundings and oxidant state of Ti and then resulted in an obvious increase in adsorbed Al and Ti2+ amount on the catalyst surface, which influenced the activity and stereoregularity for diene polymerization. [ABSTRACT FROM AUTHOR]

• Applied Universal Neural Network Potential to model Ziegler-Natta catalysts, enhancing predictive accuracy for real-world conditions. • Examined the structural and electronic influences on catalysis by creating Ti active site models on MgCl2 using molecular dynamics simulations. • Analyzed the heterogeneity of Ti active sites, showing varied impacts on ethylene insertion reactions. • Identified a specific titanium active site with a faster reaction rate for ethylene insertion, highlighting the importance of site arrangement for catalyst performance. We investigate the interaction dynamics between TiCl 4 molecules and a MgCl 2 (110) cluster to understand the complexities of Ziegler-Natta catalysts through molecular dynamics simulations. Our study reveals significant distortion of Mg atoms at the edge of cluster, influencing TiCl 4 adsorption behavior, cluster stability, and reactivity. Various TiCl 4 configurations on the MgCl 2 surface, such as octahedral and bridging forms, illustrate the versatility of surface in accommodating different molecular arrangements, affecting catalytic performance. We explore diverse adsorption sites influenced by surface topology and electronic properties, revealing a range of adsorption energies from 15.7 to 29.2 kcal/mol. This indicates a complex interplay of molecular forces, significantly impacting catalytic efficiency at distorted sites. Nudged Elastic Band calculations reveal varied activation energies for ethylene insertion, suggesting faster reaction rates at certain sites and highlighting highly favorable dynamics at Corradini type Ti active sites. All these findings offer new directions for enhancing catalyst performances. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The activation energy of ethylene polymerization is minimum when the d charge of the Ti cation is moderate. • The activation energy of ethylene polymerization is minimum when the d band center of the Ti cation is moderate. • The surface effect of the support is that MgCl 2 with different surfaces regulates the activity of the catalyst by adjusting the d band center of the active center of the catalyst. 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. MgCl 2 is a suitable support for Ziegler-Natta catalyst because its crystal structure is similar to that of TiCl 3 , and the surface effect of MgCl 2 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 MgCl 2 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. [ABSTRACT FROM AUTHOR]

Various classes of molecules like diethers, succinates, diesters, amido esters are currently being used as internal donors on MgCl2 supported titanium catalysts for isotactic polypropylene as an alternative to phthalate donors owing to their potential health risk laid down by REACH legislation. In the present paper, design and synthesis of a few novel amido ester internal donors with single chiral center (7–11) by mimicking the model amido ester 3 having two chiral centers; and their catalyst preparation method were described. Further preliminary polymerization tests with newly synthesized donor molecules were investigated and results revealed that by structurally mimicking 3 with one chiral center and also with varied substitutional patterns in ester/amido moiety decline the polypropylene activity as well as isotacticity. These donor molecules are ineffective for appropriate coordination on MgCl2 sites on inducing steric hindrance for improved isotacticity; nevertheless also induces poisoning effect for the active Ti centers leading to catalyst fouling in many cases. [ABSTRACT FROM AUTHOR]

Ziegler-Natta catalyst for propylene polymerization, which TiCl4 and di-alkyl phthalate were supported on MgCl2, was analyzed by solid state 13C NMR. It was confirmed that the spin-lattice relaxation time ("relaxation time" hereafter) of carbonyl group in phthalate was shortened with increasing measurement temperature as a general manner because of the enhancing of molecular mobility at high temperature. The degree of the relaxation period reduction with temperature was influenced by the alkyl group size in phthalate molecule; the larger alkyl group showed a greater shorting of the relaxation period. A short relaxation time should suggest a weak interaction between the phthalate molecule and the MgCl2 support surface. The change in catalytic performance was discussed by the active site formation mechanism involving the phthalate removal step. [ABSTRACT FROM AUTHOR]

Due to the important role of cocatalyst in the polymerization process employing industrially favored Ziegler–Natta catalysts, its effect on kinetic behavior, catalyst activity, and polymer properties is discussed. In this paper, triethyl aluminum (TEA) and triisobutyl aluminum (TIBA) have been used as the main cocatalyst ingredient with 10–20 mol percent of diethyl aluminum chloride (DEAC) and ethyl aluminum dichloride (EADC) cocatalysts, being neat TEA the cocatalysts with the highest activity. Moreover, TEA-DEAC and TEA-EADC cocatalysts revealed a built-up kinetic profile, while TIBA-DEAC and TIBA-EADC show a decay-type kinetic curve. According to melt flow index results, no considerable change in flowability was detected in the synthesized polyethylenes (PE). On the other hand, the ethylene insertion and chain termination mechanisms were investigated by means of density functional calculations using Ti active center located in (110) and (104) facets of the MgCl2 surface. To shed light on the bulkiness level of employed cocatalysts, buried volume (VBur) together with the two-dimensional map of cocatalyst systems were considered. Higher VBur of TIBA complex can explain its lower activity and decay type kinetic profile obtained by experimental studies. [ABSTRACT FROM AUTHOR]