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Kinetic investigations of olefin polymerization with Ziegler–Natta (ZN) catalysts provide information for understanding the mechanism of these reactions and are also necessary for development of industrial productions of polyolefins. In this chapter, the main kinetic features of olefin polymerization with heterogeneous ZN catalysts are considered as well as problems such as a deviation from the linear dependence of the rate of polymerization on monomer concentration, the hydrogen effect in ethene and propene polymerizations, and the comonomer effect, the natures of which are not yet completely clear and are discussed in the literature. For analysis of the kinetics and mechanism of olefin polymerization, data on the number of active centers and propagation rate constants are important. The main methods for determination of these kinetic parameters are discussed in this chapter. Data on the number of active centers in ZN catalysts of different composition are presented. On the base of these kinetic data, the hydrogen effect and the heterogeneity of active centers at propylene polymerization over ZN catalysts are analyzed.

This anthology summarizes contributions to Ziegler–Natta catalysis that have led through novel experimental methods to well-founded results, to continuing conclusions, and to increasing knowledge about the course of this catalysis. The complex and manifold mechanism has been elucidated in extensive kinetic studies in a half continuous tank reactor, in a plug flow reactor with oligomer distribution analysis as an additional “measuring instrument,” by dynamic NMR spectroscopy with line shape analysis, through use of 13C-enriched reacting ethylene as a molecular surveyor, and by observation of the individual behavior of a large number of particles with supported catalysts by transmission electron microscopy and video microscopy. The synopsis of the results of the different experimental methods gives assurance that we are safely on the right path.

This chapter looks back at the fascinating history of isotactic polypropylene, the first man-made stereoregular polymer, from the largely serendipitous discovery to the modern technologies for the industrial production of reactor blends with high-yield Ziegler–Natta catalysts featuring highly controlled morphology. This is also the story of a great man, Giulio Natta, winner of the 1963 Nobel Prize in Chemistry, and his team of incredibly talented young coworkers at the Milan Polytechnic, who in just a few years at the end of the 1950s elucidated the structure of the new polymer and that of the novel TiCl3-based catalysts leading to its formation. The pioneering studies that followed on chain microstructure and the origin of the stereocontrol, and the first educated guesses on the nature of the active species, are critically reviewed, and re-visited with the aid of modern experimental and computational tools and methods, to highlight the current picture of what still represents a most important and lively area of polymer science and organometallic catalysis.

The evolution of olefin polymerization catalysis since Karl Ziegler’s and Giulio Natta’s Nobel Prize-winning discoveries in the mid-1950s has involved a prolific interplay of polymer science and organometallic chemistry and led to the development and commercial deployment of catalysts that rival the activities of enzymes and systems, yielding polyolefins possessing structures and physical properties that allow them to be applied in countless applications worldwide. In contrast, commercial processes for the copolymerization of ethylene with polar monomers such as acrylate and vinyl acetate still exclusively employ free radical processes. This chapter reviews recent developments in the catalytic copolymerization of ethylene and these polar comonomers, including well-defined, single-component catalysts capable of copolymerizing (for example) acrylates and vinyl ethers to high molecular weight, linear, random copolymers.

This article reviews the polymerization of dienes by neodymium (Nd) based Ziegler/Natta-catalyst systems. Special attention is paid to the monomer 1,3-butadiene (BD). The review covers scientific as well as patent literature which was published during the last decade to 2005. For a better understanding of the recent developments the early work on lanthanide-catalyzed diene polymerization is also addressed. The most important product obtained by Nd catalysis, butadiene rubber (Nd-BR) is introduced from an industrial as well as from a material scientist's point of view. Strong attention is paid to the great variety of Ziegler/Natta type Nd-catalyst systems which are often referred to as binary, ternary and quaternary systems. Different Nd-precursors, cocatalysts, halide donors and other additives are reviewed in detail. Technological aspects such as solvents, catalyst addition order, catalyst preformation, polymerization temperature, molar mass control, post-polymerization modifications etc., are presented. A considerable part of this review discusses variations of the molar ratios of the catalyst components and their influence on the polymerization characteristics. Non-established polymerization technologies such as polymerization in bulk, slurry and gas phase as well as the homopolymerization in the presence of other monomers are addressed. Also the copolymerizations of butadiene with isoprene, styrene and alkenes are reviewed. Mechanistic aspects such as formation of the active catalyst species, the living character of the polymerization, mode of monomer insertion, and molar mass control reactions are also explained. In the summary Nd technology is evaluated in comparison with other established technologies for the production of high cis-1,4-BR. Unsolved and open questions about Nd-catalyzed diene polymerization are also presented.

L. Friebe, O. Nuyken, W. Obrecht: Neodymium Based Ziegler/Natta Catalysts and their Application in Diene Polymerization.- A. Fischbach, R. Anwander: Rare-Earth Metals and Aluminum Getting Close in Ziegler-type Organometallics.

Polymer science is an extraordinary source of very interesting mathematical problems, as it is largely testified by the recent literature. Research is extremely active in various directions: understanding the mechanical and thermodynamical behaviour of known polymers, improving production processes, designing new molecules and new materials with specific properties. A strong and continuous stimulus comes from technological applications in various fields, in which the demand of better performing materials is more and more intense.

Metallocene catalysts enable the structure of polymers to be tailored in a way which has not been reached before. However, they are more active than the conventional Ziegler — Natta catalysts only as homogeneous metalocene systems, a fact that has essentially restricted their use to industrial processes producing polymers in solution. Modern polymerization processes are solvent free slurry (with liquid monomer) or gas phase processes. To use metallocene catalysts in these modern processes, it is necessary to convert them to heterogeneous catalysts [1, 2]. However, problems have appeared chiefly concerning the activity of the supported catalysts, because heterogeneous metallocene catalysts are much less active than supported Ziegler—Natta catalysts [3,4]. Most solid systems that have been reported cause a dramatic decrease in the activity when compared with the corresponding metallocenes in the solution. Generally, developing of heterogeneous catalyst, with the metallocene as active component supported on the surface of a solid carrier, is the point of extreme interest of resent years.

The reactions of AlMe3 or Al(iBu)3 (TIBA) with the clay mineral montmorillonite form surface fixed aluminoxanes. By further addition of metallocenes — Cp2ZrCl2 or Et(Ind)2ZrCl2 — heterogeneous metallocene complexes are produced. The activities of these catalysts in ethylene or propylene polymerisation are as high as the activities known of similar homogeneous catalyst systems with MAO as cocatalyst. The reaction of AlMe3 with montmorillonite and the further addition of TiCl4 or VC14 yields very active heterogeneous Ziegler-Natta catalysts. Both types produce high molecular weighted polyethylenes.

The new method of investigation of active site non-uniformity was developed. The method is based on mass-spectrometric study of temperature programmed desorption (TPD) products from the catalyst surface at initial stages of olefin polymerization (up to 10 – 15 monomer units in chain). The method allows to obtain the information concerning the energy non-uniformity of active sites in terms of a distribution of active sites over activation energy of active Mt-C bond thermal destruction. By the method, the initial stages of ethylene and deuteroethylene polymerization with Ti-supported catalysts of different structure were studied. It is shown that the view of energy distribution of active sites depends on catalyst structure. The values of activation energy of thermal destruction of Ti-C bonds in differing active sites were estimated and energy spectra of active sites for catalysts were obtained.

This paper summarises the results of kinetic, active centre and morphological studies obtained using a number of magnesium dichloride-based catalysts when used for the polymerization of propene. In particular studies on polymerization systems using high activity catalysts such as: MgCl2 (ball milled) / EB / TiCl4 — TEA MgCl2 (ball milled) / EB / TiCl4 — TEA/MPT MgCl2 (spherical) / DIBP / TiCl4 — TEA MgCl2 (spherical) / DIBP / TiCl4 — TEA/DPDMS MgCl2 (ethoxide type) / DNBP / TiCl4 — TEA MgCl2 (ethoxide type) / DNBP / TiCl4 — TEA/DPDMS are reported and the kinetic behavior of the systems analysed.

The cyclopolymerization of 1, 5-hexadiene provides a quantitative method of investigating metallocene structure and catalytic function, as the microstructure of the resulting cyclopolymer is reflective of the chemical and stereochemical events that occur during polymerization. Eleven different zirconocene dichlorides were studied and the properties of the resulting cyclopolymers compared. The catalyst structure was correlated to the diastereoselectivity of the cyclization step in terms of the abundance of cis and trans rings in the polymer. In order of decreasing trans ring percentage the following trend was observed: Cp2ZrCl2 (84%), monoatomic-bridged zirconocenes (77%–70%), diatomic-bridged zirconocenes (69%–65%), non-bridged zirconocenes (44%–34%), and Cp2ZrCl2 (19%). The molecular weights, conversions, yields, and extent of crosslinking are also presented.

During the four decades since the early discovery of K. Ziegler and G. Natta, polypropylene has grown to be one of the largest volume plastic materials with still an enormous growth rate of about 6–8% per year. This is the result of a lot of research and optimization work on catalysts and processes done by several companies and research institutes.

A molecular mechanics analysis of models for catalytic intermediates with a racemic or a meso ethylenebis(4,5,6,7-tetrahydro-l-indenyl) ligand is presented. Models with the racemic ligand are able to rationalize the observed enantioselectivities, not only for the regioregular placements, but also for the regioirregular placements. The higher regioregularity of the polypropylene obtained by a catalytic system containing the meso (rather than a racemic) ligand could be accounted for by assuming that, in the meso catalytic complex, the chain skips back to the starting position after each monomer insertion and prior to the coordination of a new olefin molecule. The possible occurrence, at least for a peculiar metallocene complex, of a polymerization mechanism with a regular back-skip of the chain has relevant implications on the selection of suitable isospecific model sites between those proposed several years ago for the heterogenous Ziegler — Natta catalysis.

Transition metal catalysis work by Reppe et al. (1948) and Natta et al. (1958) was the starting point for a new material: polyacetylene [2, 3]. It stimulated a tremendous research effort worldwide, especially in the past two decades [4], Its history shows how results from different areas of research provide a basis for continuous scientific progress. However, unlike the contemporary polyethylene and polypropylene developments, polyacetylene is still struggling to make its way into a useful product.

Since the discovery of Ziegler-Natta catalysts and the first commercial exploitation and development of polypropylene, research has continued to understand and exploit the fundamental, molecular basis of this unique catalyst system. This understanding has expanded the potential of the polymerization process to allow development and production of olefinic polymers with unique combinations of properties never envisaged by its original discoverers. The initial titanium chloride/aluminum alkyl catalyst for the polymerization of propylene gave poor stereoregularity, resulting in a low percentage of the commercially viable isotactic polymer. The activities of the Natta Research School were directed towards a more stereospecific system and led to the first industrial process for the production of polypropylene in 1957. Although the stereoregularity of these polymers was sufficient, the efficiency of the TiCl3 catalysts was low (3000–5000 g. polymer/g. Ti) , and extracting of the polymer was required in order to remove catalyst residues and provide a practical, useful resin.

The determination of the number of active centres in Ziegler Natta polymerization continues to be of increasing interest to researchers in this field of study. Since the pioneering work of Natta (1,2) well in excess of one hundred papers containing values for active centre concentrations have appeared in the scientific literature. Many of these papers have been concerned directly with the development and applications of appropriate methods for active centre determination to both first and subsequent generations of Ziegler-Natta catalysts. Indeed recent developments of high activity catalyst systems have done much to focus interest on this area of discovery since a knowledge of the number of actual propagating centres is a prerequisite for the determination of values of the rate constant of chain propagation. A knowledge of these quantities is essential in any informed programme for catalyst characterization and development.

In the isotactic polymerization of propene using MgCl2 supported Ziegler catalysts the addition of small amounts of a Lewis base to the cocatalytic solution causes a severe reduction of the activity of the aspecific sites, but enhances the activity of the isospecific sites; further addition of the same Lewis base cause moderate inhibition of all kinds of sites. These effects are observed with a variety of components of the cocatalytic solutions: both different alkylaluminiums and various aromatic esters or aromatic silanes. These results support the idea of alkylaluminium complexed with the Lewis base as major components of the isospecific sites.

A new route to aluminium-filled polyethylene is reported in which a Ziegler-catalyst is fixed on the surface of aluminium powder. In the presence of this supported catalyst, ethylene is polymerized in suspension in a stirred tank reactor. The polymerization takes place on the surface of the filler forming a uniform shell of polyethylene around each aluminium particle.

Bisupported silica-MgCl2-TiCl4 catalysts suited for gas phase polymerization are used at 15 bars, 85–95°C for the synthesis of polyethylenes ranging from high density to linear low density. The main parameters of the reaction (temperature, pressure, monomer ratio) are studied in connection with the pecularities of the gas phase polymerization. The effect of the addition of a Lewis base to the solid catalyst on copolymerization reactivity and on the copolymer structure are studied.

More than 30 years after the discovery of transition metals and organometal lics as catalysts for olefin polymerization these catalysts did not have lost their fascination. Since 1953 when Karl Ziegler has discovered the catalytic polymerization of ethylene leading to plastically formable polymers which are mechanically stable up to temperatures of about 100 C, synthetic polymers and rubbers have made their way right into private houses. This discovery has been a main impetus for the fast growing production of plastics. The stereoselective poly merization of propylene and other long-chain a-olefins first detected by Giulio Natta leads to an even broadened field of applications. Another enforcing factor were the developments of Standard Oil of Indiana and Phillipps Petroleum Company who engaged in the polymerization of a-olefins supported molybdenum, cobalt and later on chromium catalysts which clearly indicates the wide variety of suitable systems. This kind of research acknowledged merit when in 1963 the Nobel prize of chemistry was awarded to Ziegler and Natta. Although to a great extent there is a technical application for these catalysts, up to now the nature of the active centres and many reaction mechanisms are not completely known."

The 13C NMR analysis of the steric structure of the chain-end groups resulting from the insertion of the first propene unit into the Ti-13CH2CH3 bond has been performed on polypropene samples prepared in the presence of Ziegler-Natta catalytic systems supported on differently activated MgCl2. The data show that the kind of MgCl2 activation does not influence the steric features of both isotactic and atactic sites.

The possibility of inducing the preferential polymerization of a single enantiomer from a racemic α-olefin(stereoelective polymerization) by using optically active Lewis bases firstly shown for conventional Ziegler-Natta catalysts(1), was extended by Pino and coworkers(2,3) to highlyactive systems such as MgCl2/TiCl4 ·B*/Al(i.Bu)3·B*. In this last case (-)-menthyl anisate(B*) was used both as “internal”(IB) and as “external” (EB) Lewis base. IB and EB can in general play different roles by interacting to different extent with the transition metal and the aluminum alkyl.

“Living” polymerization is of great utility both in understanding the mechanism of chain propagation reactions and in synthesizing well-defined block copolymers. In this review we deal with the development of soluble Ziegler-Natta catalysts for the living coordination polymerization of ethylene and α-olefins and discuss the possibility of synthesis of new block copolymers.

The study of the structure and morphology of nascent polyolefins obtained with hetereogeneous and soluble Ziegler-Natta catalysts has attracted the attention of many researchers, being the subject of a considerable amount of publications appeared in the patent and scientific literature (1–2). From an industrial point of view, the interest arises from the necessity in controlling the growth of the polymer particles during polymerization due to the fact that their size, shape, density and texture influence the polymerization process and manufacture of the produced polymers.

As a problem in structural chemistry the aim to characterise the catalytic site on MgCl2 based TiCl4 Ziegler Natta catalysts presents substantial difficulties. Problems centre on the instability of Ti complexes in air, and the consequent need for in-situ studies, and the dilution and dispersion of active material. The potential of x-ray absorption spectroscopy (XAS) opposite some of these difficulties makes it well suited to characterise catalyst structure. The technique uses fine structure at core level absorption edges to derive information on chemical state and near neighbour bonding round elements of specific interest. At the absorption edge information comes from transitions which occur to the valence band. For higher x-ray energies absorption fine structure (EXAFS/XANES) results from back scattering of the photo-electron by neighbouring atoms. Since XAS is concerned with local order information can be derived from amorphous systems independent of dispersion. Also, using x-rays, material is accessible in pores, at interfaces or in-situ under working environments including liquids. Taking advantage of these possibilities, using XAS at the Daresbury Synchrotron Radiation Source, we have been able to study the Ti environment in MgCl2 supported TiCl4 Ziegler Natta catalysts made by milling and precipitation. The results of the first stages of this work are presented in this paper.

In our research group, we have been investigating the mechanisms presi ding over the steric control in the Ziegler-Natta polymerizations of 1-alkenes to polymers of high or very high stereoregularity.