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In this study, commercially available, milled, and heat-treated Mg(OEt)2 were used as the precursors in the synthesis procedure of industrially-favorable supported Ziegler–Natta catalysts. The effects of milling and heat-treatment of the support were completely investigated during the catalyst synthesis and polymerization using SEM, PSD, BET, DCS, and XRD techniques. It was found that despite the support treatments had no significant effect on the elemental analysis results of the catalysts, the morphology of the catalyst pores was very sensitive to support manipulation, and bottleneck-type pores were predominated in the catalysts which were made using the non-manipulated supports. On the other hand, the catalysts which were made using the milled and not-milled supports showed a clear difference between the activity, particle size, and particle size distribution of the catalysts. Also, a high level of stacking disorder and high grain size was observed in the crystal structure of the catalyst made using the commercially available support. In the following, competition between fragmentation and replication was investigated in the synthesized samples, and an attempt was made to link the stacking disorder (in the catalyst structure) to the ease of the fragmentation process. Finally, using practical observation, a mechanism was proposed to justify the changes in the morphology of the catalysts during synthesis procedures. We claimed that milling and especially heat-treating of the support leads to the ordering of the MgCl2 stacking structure.

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.

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

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.

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.

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’.

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.

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.

Fifty years after the Nobel Prize was awarded to Ziegler and Natta, the transition-metal catalyzed polymerization of olefins remains one of the most important reactions conducted on the industrial scale and the subject of industrial as well as academic research. This introductory article will provide a short historical review of the discovery of catalyzed olefin polymerization by Ziegler, Natta, and others and its development in the years following the Nobel Prize, as well as giving insight into Ziegler-Natta polymerization for the nonspecialist.

The success of polyolefins is governed to a large extent by the development of robust and versatile catalysts offering excellent morphology control. This review highlights the major evolution steps made in the polyolefin catalyst systems in terms of productivity and possibilities to control the molecular architecture of both polypropylene and polyethylene. Starting from the initial TiCl3-types, the continuous improvement of the Ziegler-Natta catalysts in terms of performance and cost is the major factor behind their wide market penetration. On the other hand, metallocene and the other “single-site” catalysts enable an unprecedented fine-tuning of chain microstructure by ligand design. In this article, special emphasis is placed on the influence of catalyst type on polymer structure characteristics such as molecular weight distribution, stereoregularity, and comonomer distribution and, ultimately, on the end-use properties of polyolefins. It is the excellent balance among price, performance, and processability that will further strengthen the position of polyolefins as a dominant class of materials in the polymer industry.

The linear viscoelastic properties of two series of Ziegler–Natta and metallocene HDPEs (ZN-HDPEs and m-HDPEs, respectively) of broad molecular weight distribution (MWD) have been studied. Correlations between zero-shear viscosity and molecular weight and molecular weight distribution show that the breadth of the MWD for m-HDPEs plays a role. Other interesting correlations between the crossover modulus and steady-state compliance with MWD of both these classes of polymers have also been derived. Finally, the steady-shear viscosities from capillary rheometry are compared with LVE data to check the applicability of the empirical Cox–Merz rule. It is shown that the original Cox–Merz rule is applicable for the ZN-HDPEs, while it apparently fails for the m-HDPEs. However, once the capillary data for m-HDPEs are corrected for slip effects, the applicability of the Cox–Merz rule is validated for their case as well.

Two types of industrial heterogeneous Ziegler-Natta propylene polymerization catalysts, TiCl3 type and MgCl2 supported TiCl4 type, were examined by paired interacting orbitals (PIO) analysis proposed by Fujimoto et al.. The ligand located trans to propylene was found to obstruct the insertion but was essential for the stereospecific insertion of propylene. The ligand located trans to the alkyl group of the active site was found to be necessary for activating the alkyl-Ti bond. The regioselectivity and stereoselectivity of the iso-specific polymerization site on the heterogeneous Ziegler-Natta catalyst system were confirmed. The polymerization activity of MgCl2 supported TiCl4 catalyst was larger than that of the TiCl3 catalyst.

The deactivation behaviors of TiCl3/MgCl2 model catalysts with molecularly dispersed TiCl3 were investigated to clarify the role of the dispersion state of the Ti species in the deactivation of MgCl2-supported Ziegler-Natta (ZN) catalysts for propylene and ethylene polymerization. The propylene and ethylene polymerization activities of clustered Ti species supported on MgCl2 were approximately one tenth of those of isolated Ti species, which is indicative of the significance of the aggregation of Ti species in the deactivation of ZN catalysts for olefin polymerization. Moreover, the time-course depression of monomer consumption for the clustered Ti species was slower than that for the isolated Ti species in propylene polymerization, whereas the dispersion state barely affected the depression rate in ethylene polymerization. The reduction rate of the Ti species was concluded to be important for the time-course depression of propylene consumption, whereas ethylene polymerization was insensitive to the oxidation state of the Ti species.

The aryldiimine NCN-pincer stabilized neodymium dichloride combined with aluminum alkyls established a new type of homogeneous binary neutral Ziegler-Natta catalyst system. This system exhibited high activity and high cis-1,4 selectivity for the polymerization of isoprene (T p = 20 °C, 98.2%; T p = −20 °C, > 99%). Such catalytic performances remained under a broad range of polymerization temperatures and monomer-to-neodymium ratios (from 500 to 8000), reaching high number-average molecular weight (M n = 1582 kg/mol) and relatively narrow molecular weight distribution (PDI = 1.68), which was, however, influenced by the amount and bulkiness of aluminum alkyls. Dynamic investigation of the polymerization was performed, which showed the number-average molecular weight of the resultant polyisoprene had an almost linear correlation with the conversion, suggesting, in some degree, the polymerization with this catalytic system was controllable.

A novel method based on a reaction between the growing polymer chain and cinnamoyl chloride (CC) was developed to determine the number of active centers (C p ) in olefin polymerization with supported Ziegler-Natta catalysts. The reaction of titanium-polymeryl bonds in the active centers of MgCl2/ID/TiCl4-AlR3 type catalysts with CC was very fast at 20∼80 °C. Cinnamoyl labeled polymer chains were formed, which were stable in the reaction system for at least 10 min when the CC/Al molar ratio was > 1. The number of active centers was determined by measuring the number of carbonyl groups in the polymer with the UV-vis method. The C p values of the 1-hexene polymerization systems with the addition of hydrogen were also measured.

The potential energy surfaces of the initial reactions of ethylene insertion for the Ziegler–Natta catalysis with bridging groups of Cp ligands were studied by ab initio MO and density functional methods. Three metals (Ti, Zr, and Hf) in the Zeigler-Natta catalysis and eight bridging groups (BH, CH2, NH, O, AlH, SiH2, PH, and S) were treated. For the complex formation between ethylene and metallocenes, two type structures (vertical and horizon) were found. The vertical type structures are more stable in energy than the horizon types. The formation energy of the complex between ethylene and the metallocenes by incorporation of bridging atom or group is related to the geometrical hindrance and the bond interaction as shown in the case of boron bridging system.

A calorimetric investigation on the reactions of TiCl4 with phthalates in 1,1,2,2-tetrachloroethane (TCE) is presented in order to better understand the complex interactions present in Ziegler-Natta catalytic systems. The Lewis bases diethyl isophthalate (L1), diethyl terephthalate (L2) and the ortho-isomer diethylphthalate (L3), have been chosen to study how the substituent positions could influence the energy and the stoichiometry of the complexation reactions.

A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for metallocene/Ziegler-Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl4 and rac-Et(Ind)2ZrCl2. The prepared rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst was applied to the ethylenehexene copolymerization with a variation of cocatalyst species (polymerization run 1: triisobutylaluminum (TIBAL) and methylaluminoxane (MAO), polymerization run 2: triethylaluminum (TEA) and methylaluminoxane (MAO)). The effect of cocatalysts on the chemical composition distributions (CCDs) and microstructures of ethylene-hexene copolymers was examined. It was found that the catalytic activity in polymerization run 1 was a little higher than that in polymerization run 2, because of the enhanced catalytic activity at the initial stage in polymerization run 1. The chemical composition distributions (CCDs) in the two copolymers showed six peaks and exhibited a similar trend. However, the lamellas in the ethylene-hexene copolymer produced in polymerization run 1 were distributed over smaller sizes than those in the copolymer produced in polymerization run 2. It was also revealed that the rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst preferably produced the ethylene-hexene copolymer with non-blocky sequence when TEA and MAO were used as cocatalysts.

A series of cyclic dimethoxysilanes has been prepared using a one-step strategy which consists in reacting magnesium dibromoalkanes with tetramethoxysilane. The dimethoxysilacycloalkanes obtained were evaluated as the external electron donor in Ziegler–Natta catalysts for propylene polymerisation. Comparison of the experimental results with theoretical predictions using a molecular model confirmed the essential structural characteristics that are required to achieve stereospecific polymerisation of propylene. Very good activity and stereospecificity were obtained with 2,6-diethyl-1,1-dimethoxysilacyclohexane which led to results close to that of actual industrial external electron donors, cyclohexylmethyldimethoxysilane and dicyclopentyl dimethoxysilane.

Four new diester compounds were prepared and used as internal donors (ID) to prepare MgCl2 supported titanium catalysts. Different diesters had notable influences on the porosity and the specific surface areas of the catalysts. The propylene polymerizations results showed that isopropyl groups(ID-2), cyclopentyl(ID-4) were more suitable substituents for diester compounds to replace phenyl(DIBP). The effects of different external donor (ED), Si/Ti ratio and hydrogen response on new ID precatalysts were evaluated by propylene polymerization.

A midrapidity zone formed in heavy-ion collisions has been investigated through special selections of light particles and intermediate mass fragments detected in the reaction 35Cl on 12C at 43 MeV/nucleon and the reactions 58Ni on 12C, 24Mg, and 197Au at 34.5 MeV/nucleon, and of neutron energy spectra measured in the reaction 35Cl on natTa. Properties of the observables have been examined to characterize the neck-like structure formed between the two reaction partners.

Two types of inorganic supports, MgCl2 and SiO2, for the impregnation of catalysts were prepared by the recrystallization and sol-gel methods, respectively. The Ziegler-Natta/Metallocene hybrid catalysts were prepared in order to control the molecular weight (Mw) and the molecular weight distribution (MWD) during ethylene polymerization. The polyethylene produced by the hybrid catalysts can control the Mw and the MWD of polymer, showing two melting temperatures and a bimodal MWD, corresponding to products arising from each of the individual catalysts. This suggests that these hybrid catalysts acted as individual active species and produced a blend of polymers.

In this paper we construct a mathematical model for the Ziegler–Natta polymerization process which includes the initial stage of fragmentation of the support. The problem consists in a system of partial differential equations with free boundaries and extends the previous model proposed in [2, 3]. Local existence and uniqueness of a regular solution are proved.

The mechanical nonlinear behaviour of metallocene- and Ziegler-Natta catalyzed polyethylenes with various contents of short chain branching was investigated using a nonlinear constitutive equation in which the plastic deformation and the anharmonicity of elastic response are taken into account. It is suggested that the mechanical behaviour is governed by the plastic deformation for the Ziegler-Natta catalyzed polyethylenes, whereas the anharmonicity strongly affects the mechanical behaviour for metallocene-catalyzed polyethylenes.

A metallocene catalyst or a metallocene/Ziegler-Natta hybrid catalyst supported on MgCl2 was studied for application to the commercial slurry phase process and to the control of MWD of the polymer produced. The MgCl2 support was prepared by the recrystallization method with different solvents: alcohols and H2O. The recrystallized MgCl2 support was pretreated with triisobutylaluminum (TiBAL) or trimethylaluminum (TMA), methylaluminoxane (MAO), to give different supporting environments. Metallocene/Ziegler-Natta hybrid catalysts on MgCl2 were prepared by first supporting the metallocene catalyst, followed by the Ziegler-Natta catalyst after pretreatment with an alkylaluminum compound. The type of solvent plays a role in providing a suitable environment in the support for impregnating catalysts. The hybrid catalyst, whose support was recrystallized in n-propanol (n-PrOH) and pretreated with TiBAL, showed the highest molar ratio of Zr/Ti= 1/2.71. But the hybrid catalyst, whose support was recrystallized in H2O and pretreated with MAO, showed the best hybrid effect showing a variety of bimodal peaks in proportion to the ratio of MAO/TEA in GPC analysis. This effect might be due to steric factor and polarity of solvent, as well as the pretreatment material. It is concluded that the MWD of polyethylene produced by metallocene/Ziegler-Natta hybrid catalyst that is supported on MgCl2 can be controlled by regulating the amounts of MAO and TEA added as cocatalysts and by the use of different solvents and pretreatment materials.

The recoil properties of nuclides produced in the photonuclear reactions on natCu, natAg, natTa, and 197Au induced by bremsstrahlung of end-point energies (E o) of 250 to 1000 MeV have been investigated using the thick-target thick-catcher method. The obtained mean ranges of produced nuclides smoothly increase with an increase of the mass difference (ΔA) between products and target, and show E 0-independence at E 0≥600 MeV, reflecting the limiting behavior above (3, 3) resonance region. The mean kinetic energies, T, deduced from the mean ranges show the following two components; (1) (γ, xn) products by giant-resonance and/or quasi-deuteron resonance absorption, (2) (γ, xnyp) products by mainly (3, 3) resonance absorption. Slightly rapid increase of T was found around ΔA=15, 18, 24, and 25 for natCu, natAg, natTa and 197Au, respectively, reflecting a change in mechanism. Kinematic properties of the product nuclei were calculated by using the PICA (Photon-Induced Intranuclear Cascade Analysis) code. The T calculated by the PICA code at E 0=400 MeV well reproduced the experimental results of natCu, but the same calculation for natAg, natTa, and 197Au gave lower mean kinetic energies than the experimental results.

X-ray photoelectron spectroscopy (XPS) analysis was performed on TiCl4/MgCl2/EB (ethyl benzoate) catalysts, TiCl4/MgCl2 internal donor free catalysts and TiCl4·EB complex to elucidate the effect of EB on electronic state of Ti species in TiCl4/MgCl2/EB catalysts. Combined with FTIR analysis, the way that EB influenced electronic state of Ti species was postulated. XPS results showed that the binding energy of Ti2p3/2 in TiCl4/MgCl2/EB catalysts was lower than that in TiCl4/MgCl2 internal donor free catalysts indicating that EB influenced electronic state of Ti atoms by providing electrons to Ti atoms in TiCl4/MgCl2/EB catalysts.

Polymerization mechanisms on Oh- propyltitaniumchlorides and Td- propyltitaniumchlorides, active site models of TiCl3 catalysts and metallocene catalysts, respectively, are studied by using ``paired interacting orbitals'' (PIO) analysis and ``localized frontier orbitals'' (LFO) calculation. In the case of TiCl3 catalysts the possible route of an incoming ethylene is constrained by Cl anions located in the ethylene insertion plane. In the case of metallocene catalysts, such a constraint does not appear, and therefore, they should be superior to TiCl3 catalysts in catalytic activity. The low reactivities of TiCl3 catalysts are removed considerably by making Ti2n clusters on the crystalline surface.

TiCl4/SiO2, Ti(OC4H9)4/SiO2, MgCl2/TiCl4/SiO2 and MgCl2/Ti(OC4H9)4/SiO2 catalysts were prepared by treating silica gel with TiCl4, Ti(OC4H9)4, MgCl2/TiCl4 or MgCl2/Ti(OC4H9)4 in tetrahydrofuran (THF) solution. Ethylene polymerization was performed with these catalysts activated by common alkylaluminum compounds. The influence of magnesium dichloride on catalyst performance was investigated. MgCl2 has enhanced the catalyst activity for both titanium compounds. In addition, all catalyst systems were only active when they were washed with AlCl(C2H5)2 (DEAC).

The system, Fe(C17H35COO)3-Al(C2H5)3, has been studied directly in the process of cyclohexane and phenylacetylene hydrogenation. It is shown that the system composition can vary in the course of the catalytic process. The effect of unsaturated compounds on the system composition depends on their ability to serve as ligands.

Diblock copolymers of acetylene and styrene were prepared by treating Ti(OBu)4 with polystyryl lithium followed by reaction with acetylene. Reliable evidence for the formation of block copolymers was derived from dual radiotagging experiments.

X-ray studies revealed a strongtrans-influence in titanium tetrachloride-ethyl benzoate complexes. From FTIR spectra, a very strong complexation is found in a 2∶1 complex and in a surface complex on magnesium chloride supported Ziegler-Natta catalysts. In both cases the ester is proposed to betrans to a bridging chlorine.

THE kinetic behaviour in the initial stages of the polymerization of propylene with titanium trichloride–triethyl aluminium can be divided into two types: the build-up type (the rate increases to the stationary value) and the decay type (the rate approaches decreasingly to the value). Natta and Pasquon1 observed that the build-up type changed into the other type as grinding the titanium trichloride, whereas the stationary rate did not change, and supposed that the produced polymer adjusted the particle size of titanium trichloride into the stationary value appropriate for the stationary polymerization. This supposition is based on the experimental result that the same stationary rate per unit weight of titanium trichloride was obtained with the use of the titanium trichloride catalysts in various particle sizes.

THE Ziegler–Natta polymerization of α-olefines has been widely investigated by many workers mainly from the practical point of view. On the other hand, the details of the reaction mechanism are not yet clear. There are, of course, some basic investigations of the reaction by Natta et al.1, one of which is considered here; that is, the kinetic behaviour of the polymerization of propylene in the initial stages (Natta's ‘the adjustment period’), where the polymerization-rate, r, changes with the polymerization time, t, from the initial rate, r0, at t = 0, to the stationary rate, r∞. The phenomenon can be divided into two types, that is, the build-up type and the decay type. The decay type was observed with the ground catalysts (sizes ⩽ 2µ), while the build-up type was observed with the unground ones (1∼100µ). Analysing the latter types of rate change, Natta et al. found that: where tN is the polymerization time at which the rate equals ¾ of the value of the stationary rate, r∞, and P the pressure of propylene. Natta suggested that the stationary reaction corresponds to a definite particle size of the catalyst, and any other catalyst with a different particle size would alter to this definite size.

β-TiCl3 is usually prepared according to the reaction: by mixing heptane solutions of the reactants. The product thus obtained, however, is not suitable for determinations of X-ray structure, because of the poor quality of the powder patterns. Natta et al.1obtained better X-ray photographs from samples prepared by thermal decomposition of CH3TiCl3 (ref. 2). From these photographs they arrived at a crystal structure which is very similar to the structures of the needle-shaped modification of TiBr3, TiI3 and the zirconium trihalogenides3.

SEVERAL attempts to obtain X-ray diffraction patterns of crystalline white phosphorus have been made1. It is claimed by some that the ready reversion of the white to the red form under irradiation with X-rays prevents any pattern being obtained, while others suggest that the high degree of thermal motion in the crystal lattice will render it impossible to obtain anything but a few very diffuse rings. Natta and Passerini2, however, state that they obtained a well-defined powder photograph of white phosphorus with 22 lines, using iron Kα radiation at − 35° C. They claim that the substance is cubic with [a] = 7.17 A., containing four molecules of P4 per unit cell, but give no other data.