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We report on the synthesis of three perylene-tagged electron donors representing three major types – phthalates, diethers, and alkoxysilanes – which are of importance for the subsequent studies of MgCl2-supported Ziegler–Natta catalysts by means of laser scanning confocal fluorescence microscopy. The obtained products were unambiguously characterized, including by X-ray crystal structure analysis; their photophysical properties (absorption and emission spectra) were investigated as well. Additionally, a reliable and convenient protocol for the multigram synthesis of the required starting material – 3-bromo­perylene (PerBr) – was developed. The key step of this method was synthesis of trialkylsilyl-substituted perylenes, which were further separated by means of flash chromatography followed by conversion of the isolated 3-trialkylsilyl-substituted product to PerBr.

We measured the excitation functions of natTa(p,x)177,178W, natTa(p,x)176,177,178m1,180gTa, and natTa(p,x)175,179m2,180mHf reactions up to the proton energy of 44.2 MeV using the stacked-foil activation technique. The measured results were compared with the literature data as well as with the theoretical values obtained from the TENDL-2017 library based on the TALYS-1.9 code. The integral yields for thick target of the investigated radionuclides were determined from the measured excitation functions. The purpose was to provide a new data set for the formation of the investigated radionuclides applicable in medicine and industry and to provide information that could support in testing and understanding the nuclear reaction theories.

More than 50 years have passed since Ziegler and Natta shared the Nobel Prize in Chemistry for their discovery of olefin polymerization catalysts. The field of metal-catalysed polymerization has since matured, in no small part owing to the development of several high-performance catalysts. Although polymerization research has in many ways been driven by catalyst development, this has often occurred as a result of trial and error discovery of a promising motif, followed by extensive tuning of the steric and electronic properties of the ligand(s) present in the lead complex. Recently, some alternative design strategies have emerged that afforded new classes of olefin polymerization catalysts. This Perspective highlights recently designed catalyst motifs and the novel reactivity patterns they enable. Special attention is given to methods specifically designed for the copolymerization of ethylene with polar-functionalized co-monomers — challenging reactions that showcase these creatively designed catalyst motifs. The development of high-performance olefin polymerization catalysts is a major driving force in polyolefin studies. This Perspective discusses some alternative strategies for catalyst design — strategies in which existing systems are tuned beyond merely modifying the electronic and steric properties.

A “flexible cluster” model approach to Ziegler− Natta catalysts for the production of isotactic polypropylene, allowing the use of realistically sized MgCl2 monolayer clusters (up to 38 MgCl2 units) without any constraints, was employed to investigate the formation of adducts between the MgCl2 support and three industrially relevant internal donor classes, namely phthalates, succinates, and 1,3-dimethoxypropanes. The calculated adsorption modes and thermochemical data for adducts of single-donor molecules confirmed earlier literature trends only in part. Results for adducts with multiple donor molecules, in turn, did not confirm the indications of periodic models about steric repulsion between neighboring adsorbates hampering high degrees of surface coverage; as a matter of fact, such repulsions seem to be largely traceable to unnecessary constraints inherent in periodic calculations.

The majority of EPDM materials are produced by traditional Ziegler–Natta/Vanadium catalyst and process technology. In recent decades, EPDM metallocene catalyst technologies have increased the effic...

In this work, we have addressed the question of the location of electron donors (we chose ethylbenzoate, EB, for practical reasons) on the surface of MgCl2-supported Ziegler–Natta catalysts by syne...

The effect of hydrogen on the number of active centers (СР) and the propagation rate constant (kP) at ethylene polymerization over titanium–magnesium catalysts is studied using quenching by radioactive carbon monoxide (14СО). The polymerization rate drops after hydrogen was added to the polymerization medium mainly due to the decrease in the calculated kP value. The changes in the polymerization rate and the experimental kP value observed after hydrogen was added or removed are found to be reversible. The data on the effect of the [H2]/[C2H4] molar ratio in the gas phase within the range of 0.125–1 on polymerization rate and the СР and kP values are obtained. Reduction of the kP value and a small decrease in the number of active centers are observed at the H2/C2H4 molar ratio ≥ 0.5. These findings were used to propose a scheme interpreting the effect of hydrogen on the СР and kP values. The scheme suggests that the decrease in the calculated kP value observed in the presence of hydrogen is related to the reversible formation of temporarily inactive dormant sites containing the titanium–polymer bond.

This paper presents the results of experimental determination and computational simulation of the independent cross sections of 178m2 Hf production in nat Ta and nat W thin targets irradiated by mono-energetic proton beams in the energy range from ∼ 0.04 up to 2.6 GeV. The cross sections were determined using the γ -spectrometry technique without chemical separation of irradiated samples. The obtained experimental results were compared with the results of simulations based on the modified CEM03.03-ext intranuclear cascade model, which allows to analyze both the cross sections of residual nuclei production and the probabilities of long-lived isomeric states formation. Verification of the isomeric yield calculation model was demonstrated based on experimental data on high-spin isomer production cross sections in 208Pb target irradiated by protons.

It was well known that the defects in the polymer chains could significantly influence the crystallization process of semi-crystalline polymers. In this work, the role of defect distribution in the melt memory effects was studied by comparatively investigating a pair of Ziegler-Natta and metallocene-made isotactic polypropylene (ZN-iPP and M-iPP) fraction specimens with the same total defect content which were obtained from two raw parent samples through the solvent extraction. The characterization results of melting behaviors, polymorphic structures, and the successive self-nucleation and annealing analysis demonstrated that these two fractions exhibited the different distribution of defects, i.e., the defect distribution in the M-iPP specimen was random while that in the ZN-iPP specimen was nonstatistical. The results of self-nucleation (SN) experiments indicated that the M-iPP exhibited much wider temperature range of Domain II than the ZN-iPP with similar total defect content, which indicated that the M-iPP showed a much stronger melt memory effect. Considering the effect of the microstructure on the crystallization behavior and the sequences containing defects could be excluded from the crystalline regions during the formation of crystal, we speculated that the random distributed defects in M-iPP could form a continuous interface between the crystalline regions and amorphous phase which could cause a heterogeneous melt and strengthen the melt memory effect.

Density functional theory (DFT) has been used for the study of ethylene polymerization in the Ziegler–Natta (ZN) olefin polymerization system for eight different alkoxy group containing titanium catalysts (Cat-A–H), Ti(III)Et(OR)(OR′) (where R = −CH3, – Et, −tert-butyl, −cyclohexane, R′ = −CH3, −Et, −tert-butyl, −cyclohexane). What is of significance is that the catalysts studied were all considered to be tethered to the (104) MgCl2 surface, which has traditionally been considered a “dormant” surface in ZN catalysis systems, in contrast to the “more active” (110) MgCl2 surface. Our calculations indicate that the binding of all the catalysts to the (104) surface is favorable, even after taking entropic effects into account. For purposes of comparison, ethylene polymerization has been investigated for the Cat-C (TiEt(OEt)2) and the Cat-H (TiEt(Cl)(OC4H8Cl)) (OC4H8Cl = the chlorobutoxy group) cases, for both the (i) (110) and the (ii) (104) MgCl2 surfaces. It has been seen that for both (i) and (ii) the ener...

Polymers have become indispensable in the 21st century, and today we cannot imagine life without them. However, till around the beginning of the last century, the science of polymers was considered a very primitive discipline, and majority of the scientific community did not believe that polymers even existed. Hermann Staudinger, among others, fought a long battle to convince the scientific community that polymers are real and that they are long chain molecular entities. Building on this rational bedrock of polymer science, Prof. Karl Ziegler laid the foundation of ethylene polymerization. As outlined by Dr. Sivaram in his articles on Ziegler and Natta, careful observations and systematic analyses of serendipitous results enabled Ziegler to deveop the enormously significant ‘Mulheim atmospheric polyethylene process’. A decade later, Cossee and Arlman revealed the mechanism of this polymerization reaction, which is called ‘insertion polymerization’. Insertion polymerization is popularly known as the ‘Ziegler–Natta polymerization’, in recognition of its founding fathers. Today, the world produces about 180 million tons of polyolefins annually, and polyethylene or polythene has become a household name. In this article, I shall present an overview of Ziegler–Natta polymerization. I will highlight the mechanism of this reaction, and outline the progress made in the last seven decades using some real-world examples. The last part of this artificle will take a stock of the unresolved challenges posed by Ziegler–Natta polymerization, briefiy discuss current solutions, and reiterate the enormous potential of this seventy-year-old reaction to meet contemporary challenges.

This article focuses on the different components that make up Ziegler–Natta olefin polymerization systems and shows how investigating the interactions between these components through computational approaches provide crucial information about the chemistry of these systems. Hence, the necessity of theory acting as a counterpoint to experiment is revealed, underlining the importance of computational chemistry in attacking important problems of the day.

The name of Natta is entwined inextricably with that of Ziegler, in the famous catalyst systems known by their names and used to make polyethylene and polypropylene. Unlike ethylene, which is achiral, propylene is a prochiral molecule and upon polymerization can lead to interesting stereochemical and regiochemical enchainment sequences. Natta’s prescience in recognizing this unique feature of propylene led to the discovery of crystalline isotactic polypropylene and the beginning of a new industry. The story of how Natta discovered polypropylene is an engrossing one – one of stiff competition amongst contemporaries, Natta’s intimate relationship with the Italian industries, and his unique scientific background. Natta’s identification of isotactic polypropylene as a righthanded three fold ‘single helix’ in March 1954, in quick succession to the discovery of DNA ‘double helix’ by Watson, Crick, and Rosalind Franklin (March 1953), and the coiledcoil motif of ‘triple helix’ of collagen by G N Ramachandran (August 1954), makes this period the ‘golden age of macromolecular crystallography’.

Polyethylenimines, polymers bearing amino functionalities, are studied for the first time as internal electron donors for Ziegler–Natta catalysts. An advantage of polyethylenimines (PEIs) compared to the conventional phthalate electron donors is their relative harmlessness. Interaction of PEI with MgCl2 support was studied using computational (DFT; M06-2X) and experimental (PXRD, DRIFT, CP/MAS 13C NMR) methods. Quantum chemical calculations suggest that the structural variations in PEIs significantly affect their ability to stabilize the catalytically relevant MgCl2 surfaces. Coordination on the (104) surface seems to be favored upon consideration of the layered structure of MgCl2. The surface stabilization energies of branched PEIs are of the same magnitude with a phthalate electron donor reference. Experimental results indicate, in agreement with theoretical results, a strong coordination ability of branched PEI through nitrogen atoms to MgCl2. Based on spectroscopic data, nitrogen atoms of primary, sec...

A series of (SiO2/MgO/ID/MgCl2)·TiCl x Ziegler-Natta catalysts for propylene polymerization has been prepared with a new method. These catalysts were synthesized using soluble Mg-compounds as the Mg-source and the preparation progress was relatively simple. The catalyst could copy the spherical shape of the carrier very well. The propylene polymerization results showed that the catalyst revealed the best activity with 9,9-di(methoxymethyl)fluorene (BMMF) as internal donor at 50 °C with the optimal molar ratio Al/Ti = 5, which was much lower than what the industrial polypropylene catalyst used (at least molar ratio Al/Ti = 100), resulting in great cost saving. Additionally, the polymerization kinetics of the catalyst exhibited very stable property after achieving a relatively high value. These catalysts possessed rather high activity and good hydrogen response. The isotactic index (II.) value of the PP products could be higher than 98% in the presence of both internal and external electron donors. Moreover, temperature rising elution fractionation method was used to understand the influence of donors and H2 on the properties of the PP products.

Medium- and high-resolution SEM analysis of several Ti-based MgCl2-supported Ziegler–Natta catalysts and isotactic polypropylene produced with them is carried out. Each catalyst particle, 35–55 μ in size, produces one polymer particle with an average size of 1.5–2 mm, which replicates the shape of the catalyst particle. Polymer particles contain two distinct morphological features. The larger of them are globules with Dav ∼400 nm; from 1 to 2 × 1011 globules per particle. Each globule represents the combined polymer output of a single active center. The globules consist of ∼2500 microglobules with an average size of ∼20 nm. The microglobules contain several folded polymer molecules; they are the smallest thermodynamically stable macromolecular ensembles in propylene polymerization reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3832–3841

Titanium-magnesium Ziegler-Natta catalysts are the basis of the modern processes for polypropylene production. These catalysts have been the object of numerous studies for many decades. Nevertheless, the structure of the catalysts remains a significant research focus. One of the major questions to be answered is the nature of the active sites precursor − the titanium compound, its form and structure on the surface of the catalysts. In the present study, the experimental data show that the precursor of the catalyst active site is TiCl 4 , which is weakly bound to the surface of the catalyst. This TiCl 4 is able to migrate outside the catalyst particles and to adsorb on activated MgCl 2 , giving rise to new precursors of the active sites. The quantity of TiCl 4 , which is able to migrate easily, amounts to about half the total amount of titanium compounds in the catalysts. At the same time, the rest of titanium is tightly bound to the catalyst surface and does not produce the active sites.

This paper describes our recent results in the field of zirconocene-catalyzed α-oltfin transformations, and focuses on questions regarding the reaction mechanism, rational design of zirconocene pre-catalysts, as well as prospective uses of α-olefin products. It has been determined that a wide range of α-olefin-based products, namely vinylidene dimers, oligomers and polymers, can be prepared via catalysis by zirconocene dichlorides, activated by a minimal (10–20 eq.) amount of MAO. We assumed that in the presence of minimal quantities of MAO, various types of zirconocene catalysts form different types of catalytic particles. In the case of bis-cyclopentadienyl complexes, the reactive center is formed under the influence of R2AlCl, which makes the chain termination via β-hydride elimination significantly easier, with α-olefin dimers being formed as the primary product. Bis-indenyl complexes and their heteroanalogues, form stable cationic catalytic particles and effectively catalyze the polymerization. Mono-indenyl and mono-substituted bis-cyclopentadienyl-ansa complexes catalyze α-olefin oligomerization. Effective catalysts of dimerization, oligomerization and polymerization of α-olefins in the presence of minimal MAO quantities are proposed. Prospects of using α-olefin dimers, oligomers and polymers in the synthesis of branched hydrocarbon functional derivatives (dimers), high quality, low viscosity motor oils (oligomers), and thickeners and absorbents (polymers) are examined.

The nature of Ti(III) species, introduced in working models of industrial Ziegler Natta catalyst precursors, consisting of MgCl2/TiCl4 binary systems, eventually containing different Lewis basis, are studied by a combination of X- and Q-band CW and pulse EPR spectroscopy. In Ziegler Natta catalysts, Ti(III) play the double role of active catalytic species and unconventional spin probes. On the binary system, two dominant Ti(III) species, characterized by distinctively different EPR spectra, are observed. 35,37Cl Q-Band HYSCORE spectra allow estimating the hyperfine and nuclear quadrupole interactions of directly coordinated Cl, characterized by a hyperfine dipolar contribution of the order of 5 MHz and nuclear quadrupole interactions of the order of e2qQ/h = 9 MHz. Interestingly, the two dominant EPR active species are selectively suppressed by the presence of different Lewis bases, indicating the possibility to address the long standing issue of the influence of Lewis bases in driving specific morphological configurations and influencing the catalytic properties of Ti(III) active sites.

Isotactic polypropylene (i-PP) is mainly produced with heterogeneous Ziegler-Natta (ZN) catalyst systems. Direct structural information on the active species is very difficult to achieve; as a matter of fact, the 13C NMR microstructure of the polymer has long been used as an indirect "fingerprint". For a long time, however, the intrinsically poor sensitivity of natural abundance 13C NMR spectroscopy hampered a complete evaluation of the microstructure, and many rare albeit important details escaped detection with standard tools and methods. The most prominent case is that of the regiodefects, which are specially important because they dictate ZN catalyst response to molecular hydrogen used as a chain transfer agent. In recent papers we have reported on the quantification of regioirregular 2,1 units in ZN i-PP by means of high-temperature cryoprobe 13C NMR. Here we shift the focus onto the stereochemical environment of such units, which was highlighted by comparing the spectra of suitable ZN PP fractions with those of model PP samples made with molecular catalysts of different structures and symmetries. The results lend support to our three-site model of ZN catalytic species, originally based on the stereochemistry of regioregular PP chains/blocks.

International audience; Ziegler-Natta precatalysts were synthetized from Lewis-base-modified-MgCl2 supports and treated by various Lewis acids, prior to activation by triethylaluminum, in order to increase their activity in ethylene polymerization. BCl3 provided the highest increase in activity. Interestingly, polymerization results showed no substantial modification of polymer properties, which is consistent with the Lewis acid only promoting the creation of new active sites, after activation by TEA, possessing very similar features than the original ones achievable with conventional precatalysts (i.e. without Lewis-acid treatment).

The stopped-flow (SF) technique has been extensively applied to study Ziegler–Natta (ZN) olefin polymerization kinetics within an extremely short period (typically

Chemical routes for preparing Ziegler-Natta (ZN) catalysts accompany the formation of by-products that remain in final catalysts in different amounts. In the history of ZN catalysts, much less emphasis has been given to analyze such by-products present in catalysts. Herein, we prepared various Mg(OEt)2-based ZN catalysts and conducted solution-state NMR measurements to characterize and quantify the organic components of these catalysts. It was found that, depending on the molecular structure of the internal donor (ID) and catalyst preparation conditions, an ID can undergo side reactions to produce organic by-products. All the catalysts contained different amounts of titanium alkoxy by-products formed in the reaction between Mg(OEt)2 and TiCl4, which were detrimental for the catalyst activity. These by-products were responsible for increasing the amount of the amorphous fraction in polypropylene and decreasing the highly crystalline fraction's stereoregularity. Possible hypotheses to explain the negative impacts of titanium alkoxy by-products are discussed.

A mathematical model of the process of producing polyisoprene in the presence of various catalytic systems of the Ziegler-Natta type is constructed in the article. When developing a mathematical model, the polycentric nature of the applied catalytic system was taken into account and the modular construction principle was applied, which allows calculations to be made both for the batch mode of the process and for the continuous mode. An analysis was also made of the influence of the hydrodynamic regime on the polymerization rate and the molecular characteristics of the resulting product using the example of a titanium-containing catalyst system.

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

Full quantum chemical calculations, using density functional theory (DFT), have been conducted to explain the effect of donors on the “activation mechanism” in the Ziegler–Natta (Z–N) catalyst system. In the activation mechanism, the inactive TiIVCl4 catalyst converts into the active TiIIICl2Et catalyst with the help of the AlEt3 present in the system. The donors that have been considered in this study are: ethyl benzoate (eb), two representative diether cases, a phthalate donor, and a silyl ester donor. The results indicate that eb and the diether donor cases donor have a negative effect on the barriers for the activation mechanism. However, the eb donor can be displaced from the MgCl2 surface by AlEt3, which matches experimental observations. For the phthalate, silyl ester and TiCl3–OC4H8Cl cases, the results indicate that a significant induction period would be present in Z–N systems employing such donors or having such a catalytic center, before catalysis could commence.

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

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

Ziegler–Natta catalysts are one of the most important industrial catalysts for the production of isotactic polypropylene, yet they are still not properly understood at the molecular level. We explo...

In this introductory lecture I will try to summarize Natta’s contribution to chemistry and materials science. The research by his group, which earned him the Noble prize in 1963, provided unprecedented control over the synthesis of macromolecules with well-defined three-dimensional structures. I will emphasize how this structure is the key for the properties of these materials, or for that matter for any molecular object. More generally, I will put Natta’s research in a historical context, by discussing the pervasive importance of molecular geometry in chemistry, from the 19th century up to the present day. Advances in molecular graphics, alongside those in experimental and computational methods, are allowing chemists, materials scientists and biologists to appreciate the structure and properties of ever more complex materials.

The penta-ether compound was synthesized by the reaction of di(trimethylolpropane) with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl2-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional Ziegler- Natta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl2-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a penta-ether/Mg molar ratio equal to 0.21.

The electron paramagnetic resonance (EPR) method was used to investigate the formation of alkylated Ti(III) species in superactive titanium–magnesium catalysts with a low titanium content during their interaction with an organoaluminum activator (AlMe3), as well as the interaction of alkylated Ti(III) surface species with carbon monoxide. EPR data on the content of alkylated Ti(III) species in these catalysts agree well with the number of Ti–R bonds that are determined after the interaction of radioactive carbon monoxide (14CO) with catalyst activated by triethylaluminum in the absence of monomer. Parameters of EPR spectra of the Ti(III) species having different structure and composition on the surface of titanium–magnesium catalysts were calculated by quantum-chemical simulations. The calculated g-values are consistent with the g-values observed in EPR spectra of the catalysts. Analysis of the literature data and results of our study made it possible to propose the parameters of EPR spectra characterizin...

Using periodic DFT, the present study evaluated the interactions of donors with MgCl2 surfaces. The selected donors included 1,3-dimethoxy-2,2-dimethylpropane, dimethoxydimethylsilane, and dimethyl phthalate. The absorption energies and distances of Mg–O were obtained from α-MgCl2 (110), (100), and β-MgCl2 (110), (100), and (104) surfaces. Donors on α and β-MgCl2 (110) surfaces reflected the largest absorption energies among the complexes examined. Results indicated that the surface of MgCl2 was controlled by choosing an appropriate electron donor. Findings indicated that control of the MgCl2 surface may be achieved by selecting an appropriate electron donor. The results of the present work indicate that control of the MgCl2 surface was attainable by appropriate selection of an electron donor; such a concept was utilizable in heterogeneous Ziegler–Natta olefin polymerization catalysis.

The structural, vibrational, and electronic properties of silica-supported Ziegler–Natta catalysts industrially relevant for polyethylene production were investigated in detail by means of a multitechnical approach at each step of catalyst preparation, including precatalyst activation. In the precatalyst, the TiClx phase is grafted mainly to the silica surface and almost independent of the supported MgClx phase. However, the subsequent activation by means of an aluminum–alkyl compound causes important changes to both the supported MgClx phase and the TiClx phase. The resulting catalyst is entirely reconstructed so that most of the titanium sites are detached from the silica surface and in interaction with a highly dispersed MgCl2 phase, thus mimicking the most famous and highly investigated Ziegler–Natta catalysts (not silica-supported). For the first time, the catalyst performances were monitored by means of in situ FT-IR spectroscopy in transmission mode, simulating industrially significant polymerizati...

The present article proposes a simple way to dramatically alter the pore architecture of Mg(OEt)2-based Ziegler–Natta catalysts by the addition of a small amount of i-propanol during the synthesis of Mg(OEt)2. The incorporated i-propoxide distorts the crystalline structure of Mg(OEt)2, finally causing the phase transformation and significant densification of particles. Such modifications completely alternate the pore architecture of resultant catalysts, which contribute to the design of catalytic properties.

Olefin polymerization using Ziegler–Natta catalysts (ZNCs) is an important industrial process. Despite this, fundamental insight into the inner working mechanisms of these catalysts remains scarce. Here, we focus on the low-γ nuclei 25Mg and 35Cl for an in-depth solid-state NMR and density functional theory (DFT) study of the catalyst’s MgCl2 support in binary adducts prepared by ball-milling. Besides the bare MgCl2 support and a MgCl2–TiCl4 adduct, samples containing donors that are part of the families of 2,2-dialkyl-1,3-dimethoxypropanes and phthalates used in fourth- and fifth-generation ZNCs are studied. DFT calculations indicate that the quadrupolar coupling parameters of the chlorines differ significantly between bulk and surface sites. As a result, the NMR visibility of the chlorine sites correlates with the particle size except for the adduct with 2,2-dimethyl-1,3-dimethoxypropane donor. The DFT calculations furthermore show that the surface sites are fairly insensitive to binding of different do...

The most commonly used cocatalyst species in Ziegler-Natta catalysts are aluminium alkyls. In this study we aim to find the interaction between aluminium centres of these activators and other components in the ZNC system. Initially we look at binary systems of Al-alkyl/MgCl2 and ternary systems of Al-alkyl/MgCl2/TiCl4, followed by donor containing systems. The aluminium alkyls prove to be very reactive species and only in the case of trimethylaluminium the alkyl is strongly present in the sample. This species appears to convert, however, over time. 1H NMR proves to be an efficient method to detect the presence of the Al-alkyl species. The use of high magnetic field strengths and 27Al MQMAS NMR alleviates signal overlap and gives insight in the dominant line broadening mechanisms thus providing an in-depth view of the cocatalyst. Various Al species with different coordinations can be identified in the samples. The heterogeneity of the samples turns out to have a larger effect on the 27Al NMR spectra than the quadrupolar interaction, which argues against the presence of highly distorted sites with mixed coordinations. Nevertheless for the samples indicating the presence of alkyls in the 1H NMR spectra, we observe an aluminium site at 97 ppm in the 27Al spectra that might be coordinated to an organic group.