Search

A full elucidation of chemisorbed donor behavior is of fundamental importance for tailoring the active species but has not yet been achieved for Ziegler–Natta catalysts. Herein, by exploiting the s...

Although Ziegler-Natta catalysts were discovered more than four decades ago, many aspects of their characteristics are not fully understood. The effect of the support particle size on the final pro...

Many researchers have studied the effects of donors, promoters and alkyl aluminum compounds on the polymerization catalysts, the polymerization process and the final properties of polymers. Neverth...

The effect of nanosize and structural disorder on the MgCl2 support of Ziegler–Natta catalysts has been investigated in terms of induced changes to their vibrational spectroscopic fingerprint. In p...

Herein, we study comparatively melt-memory effects on recrystallization of two sets of linear low-density polyethylenes (LLDPE) synthesized with Ziegler–Natta (ZN-LLDPE) and with metallocene cataly...

The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl4/MgCl2 Ziegler-Natta (Z-N) catalysts are determined by the structure and nature of active centers, which are mysterious and fairly controversial. In this work, the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers [C*] with different tacticity. SEM was applied to characterize the catalyst morphologies and growing polypropylene (PP) particles. The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS. The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method. The catalytic activity, active centers with different tacticity and propagation rate constant kp, fragmentation of the catalyst, crystalline structure of PP are correlated with temperature and time for propylene polymerizations. The polymerization temperature and time show complex influences on the propylene polymerization. The higher polymerization temperature (60 °C) resulted higher activity, kp and lower [C*], and the isotactic active centers Ci* as the majority ones producing the highest isotactic polypropylene (iPP) components showed much higher kp when compared with the active centers with lower stereoselectivity. Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation. This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles, and provide the solutions to the improvement of catalyst activity and isotacticity of PP.

This paper presents the results of study of titanium–magnesium catalysts often used in polymerization processes, by photoluminescence spectroscopy (PL) in combination with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interaction of dibutyl phthalate (DBP) with MgCl2was studied at DBPadded/Mg = 0–1 (mol/mol). The luminescence spectra with excitation at 278 nm and the excitation spectra for main emission bands were recorded. It was shown that DBP adsorbed on magnesium chloride, both in the form of donor–acceptor complexes (D+A–) and in the form of molecular complexes. At DBPadded/Mg +A–complexes occur predominantly; with an increase in DBPadded/Mg, the fraction of molecular complexes increases. Molecular complexes are destroyed during the treatment of the support by TiCl4. In this case, the structure of magnesium chloride is disordered and new coordination–unsaturated sites are formed. This work is a first attempt to apply PL spectroscopy in combination with DRIFTS spectroscopy to study titanium–magnesium Ziegler–Natta catalysts. The application of PL spectroscopy to such systems made it possible to detect interactions within and between donor molecules, which would be particularly challenging to achieve using other spectroscopic methods. Both spectroscopic methods provided crucial information about the existence of two types of complexes on the sample surface which is important for tuning the synthesis procedure of the titanium–magnesium catalysts for olefin polymerization.

1,9-decadiene/propylene copolymerization is assessed as a way for Ziegler-Natta catalysts to access long chain-branched polypropylene. A MgCl2/9,9-bis-(methoxymethyl)fluorine/TiCl4 catalyst with tr...

This study reported novel eco-friendly Ziegler-Natta catalysts containing bio-derived maleic rosinate tri-n-butyl and maleic rosinate tri-n-octyl as internal electron donors for propylene polymeriz...

The scientific and technical advances in the field of polymer science has been abundant in recent years. Amongst the various polymeric materials available in market, synthesis of polyolefins has been in the forefront since decades. A major challenge in this domain remains in attaining stereoregular polyolefins especially polypropylene (PP) and significant efforts were carried out by synthesizing various internal donors (ID) aiding the catalysts involved in producing them. This short review gives an overview of i) various generations of Ziegler–Natta (ZN) catalyst systems ii) general classes of ID that has been demonstrated by the researchers over the past decades iii) their influence on PP isotacticity and polymer properties. The coordination modes of different donor classes on supported ZN system and comparative study especially between phthalate and diether ID classes were also addressed here. This review also presents the studies carried out on phthalate catalyst structure analysis, detailed comparison study on phthalate and diether IDs in terms of PP isotacticity, regioselectivity, hydrogen response, and also their cross combination study and competitive behavior. Further a brief description on other structurally varied IDs like malonates, maleates, silyl diol esters, bifunctional donors, multi ether donors demonstrated for isotactic PP were also presented. Studies conducted on compatibility of incorporation of two different classes of IDs on a single supported ZN system for the fundamental understanding of the catalyst behavior; and also on how mixed donor approach enables in tuning the catalyst for polymer properties were also presented. This review also provides an opportunity to the young minds and the basic researchers from academic point of view by and large to create new polymeric materials with useful properties or modify the existing materials for new applications by incorporating new IDs for further improvisation of the stereo regularity in obtaining the polymers. Graphic Abstract

Two series of polypropylene samples (PP) were prepared with two MgCl2/TiCl4-type catalysts with diisobutyl phthalate and 9,9-bis(methoxymethyl)fluorine as internal donors (named as cat1 and cat2), ...

MgCl2 supported Ziegler–Natta (Z–N) catalysts have emerged as the most exciting chemical process for polyolefin technology, which is responsible for the production of ∼150 million tons of polyolefin (polyethylene and polypropylene) per annum. However, fundamental chemistry of Z–N catalysts is not fully understood yet due to their multi-component nature as well as heterogeneous systems. Therefore, in this review, we have highlighted the chronological development of a heterogeneous Z–N catalyst and its polymerization (ethylene, propylene and 1-butene) process including termination steps. Then, we have discussed different structural and chemical aspects of the catalyst support, catalytically active sites, cocatalyst, internal/external electron donors and their different combinations. In the last two decades, density functional theory (DFT) has been employed in Z–N systems to strengthen the experimental work as well as to understand mechanistic aspects of Z–N systems. Future directions of Z–N catalysts have also been discussed.

The crystallization behavior of butene-ethylene random isotactic copolymers prepared with a Ziegler-Natta catalyst, in particular the surprising crystallization of form II of isotactic polybutene in samples with a high ethylene concentration, provides novel evidence of the long-debated blocky molecular structure of these "random" copolymers.

Advanced High Throughput Experimentation (HTE) methods were applied to quantify the regioselectivity and the so-called "hydrogen response" in propene polymerization of four Ziegler-Natta catalysts representative of the three latest industrial generations (i.e., modified with a dialkyl phthalate, 1,3-dimethoxypropane or dialkyl succinate Internal Donor), used in combination with AlEt3 and a library of eight alkoxysilane External Donors with large structural diversity. At odds with stereoselectivity, regioselectivity turned out to be only modestly impacted by the chemical structure of the electron donors used as surface modifiers. A clear and simple relationship between regioselectivity and "hydrogen response", and, therefore, polymer molecular weight modulation was highlighted.

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

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

This chapter presents fascinating insights into the research that earned its investigators Nobel Prizes in the field of organometallic chemistry: Karl Ziegler and Giulio Natta for olefin polymerization catalysts (1963), Ernst Otto Fischer and Geoffrey Wilkinson for sandwich compounds (1973), Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa for electrically conductive polymers (2000), William S. Knowles, Ryoji Noyori and K. Barry Sharpless for asymmetric catalysis (2001), Yves Chauvin, Robert H. Grubbs and Richard R. Schrock for olefin metathesis (2005), and Richard F. Heck, Eiichi Negishi and Akira Suzuki for Pd-catalyzed cross-coupling reactions (2010).

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

In this contribution, novel bio-derived rosin acid ester compounds have been developed and used as internal electron donors to prepare MgCl2 supported titanium catalysts for propylene polymerization. The results of the polymerization showed that tri-n-amyl maleate, triiso-amyl maleate and tri-n-heptyl maleate as internal electron donors in Ziegler-Natta catalysts all have high polymerization activity and stereoregularity. In particular, the Ziegler-Natta catalyst with tri-n-amyl maleate as the internal electron donor has the highest activity (up to 33.4 kgPP·gCat−1·h−1) for propylene polymerization and the isotacticity of polypropylene is as high as 96.8% determined by 13C NMR. Simultaneously, the obtained polypropylene with a relatively broad molecular weight distribution of 9.0 and melt flow rate of 160.3 g/10 min, which is beneficial to processing and has practical industrial application value when used as the basic material of melt blown cloth for medical mask.

This data article provides a dataset of the energetically accessible structures including the most stable structures of xMgCl2/yTiCl4 nanoplates (x = 6–19, y = 0–4). TiCl4-capped MgCl2 nanoplates are regarded as the building block of the Ziegler–Natta catalyst. The most stable structures were determined for MgCl2/TiCl4 nanoplates of different sizes and chemical compositions using a combination of the genetic algorithm and the DFT geometry optimization. The evolution in the genetic algorithm produced a number of meta-stable structures. A set of isomeric structures having similar energy to the most stable structure (termed energetically accessible structures) are provided as realistic models of MgCl2/TiCl4 nanoplates. These structures are useful for further investigation on the structural distribution of Ti species on MgCl2 regarding the Ziegler-Natta catalyst.

The history of polymers in Italy certainly begins with Giulio Natta and the discovery of isotactic polypropylene [1,2], culminated in the delivery to Prof. Natta of the Nobel Prize for chemistry in 1963. Before those years, thanks to the development of the hydrocarbons and petrochemical sector by Montecatini (General Society for the Mining and Chemical Industry), the foundations for the development of macromolecular chemistry in Italy had been laid, but the real expansion occurred between 1958 and 1967 with a sector growth of 30% on an annual basis [3]. The research of Natta and his collaborators, on metal-organic catalysis applied to the polymerization reactions of -olefins and other unsaturated monomers, promoted the growth and consolidation, in Italy, of a network of industrial centers and academic institutes operating in the polymer science and technology sector, creating international skills. Since that period until today, Italy has kept pace with other countries and has certainly contributed to the development of the polymeric materials sector. Today, polymer science and technology in Italy represents a long-lasting and interdisciplinary field in which chemistry, physics, and engineering mix together to produce studies, which are considered among the best in the world. Several research groups coming from very different fields often collaborate in the design of the material, of the part, and of the processing technology to obtain innovative products with outstanding, new, and smart properties. Examples of the contributions of Italian research in the field are spread out in the top Journals and Conferences throughout the world. This Special Issue, which consists of 22 articles, including two review articles, aims at collecting an overview of Polymer Science and Technology in Italy, hoping that it can portray the state of the Polymeric Research in Italy and give the rest of the world a bright image of what is carried out in the field in our country.

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...

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.

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

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.

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

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.