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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.

Specific surface area based on the BET method in N 2 adsorption has historically posed poor correlation with olefin polymerization activity of heterogeneous Ziegler-Natta (ZN) catalysts. We have investigated the validity of the BET surface area for ZN catalysts based on the α S -plot method, where non-porous core–shell MgO/MgCl 2 /TiCl 4 catalysts were used as a reference material. The α S -plots for typical industrial ZN catalysts clarified the presence of two classes of micropores and resultant difficulty to isolate a multilayer adsorption region for the BET method. The results cast doubt on the application of the BET method to evaluate the surface area of heterogeneous ZN catalysts.

The extended Huckel molecular orbital method has been used to study models of the active site for Ziegler-Natta catalyzed olefin polymerization on the surface of crystalline TiCl3 containing from one to twenty titanium atoms, and the coordination of an ethylene monomer by the active site. Significant differences are observed in the coordination of ethylene to the small model systems compared to the larger model systems. These differences are analyzed using the complexation energies, bond orders and orbital populations, and are interpreted in terms of back donation from low-lying d-orbitals of the active site to the π* orbital of the olefin. Conclusions are drawn on the basis of these results regarding the requirements of model active sites suitable for study with more sophisticated theoretical methods.

Ethylene-hexene copolymers were produced using a metallocene/Ziegler-Natta hybrid catalyst supported on modified silica-magnesium bisupport (SMB). Chemical composition distributions (CCDs) and microstructures of ethylene-hexene copolymers were analyzed by stepwise crystallization and 13 C NMR analyses, respectively. It was found that average sequence length of 1-hexene was not changed significantly and CCD was extended into lower temperature region with increasing 1 -hexene content.

Two types of inorganic supports, silica-based and magnesium-based, were prepared by the sol-gel and the recrystallization method, respectively. The polyethylene produced by the Ziegler-Natta/Metallocene hybrid catalysts showed two melting temperatures and a bimodal MWD, corresponding to products arising from each of the catalysts. This suggests that the hybrid catalysts acted as individual active species and produced a blend of polymers.

Publisher Summary There has been extensive investigation on crystallization kinetics of isotactic polypropylene (iPP). Another reason for the numerous references on iPP spherulite radial growth rates might be the straightforward determination by conventional optical microscopy techniques for a large gamut of isothermal crystallization temperatures. In this chapter, the effects of MW, MWD (molecular weight distribution), and tacticity are quantified on spherulite growth rates G of iPP for isothermal crystallization temperatures within regime 3. Spherulite growth rates, as opposed to overall growth rates, are expected to be independent of metastable nuclei concentration. The chapter reports a quantitative description of iPP spherulite growth rate G as a function of isothermal crystallization temperature Tc, number average molecular weight Mn, and concentration of atactic PP. The effects of the molecular parameters are independent of Tc. While the dependency of G on Mn is small, it is highly significant. To decouple effects of molecular weight from effects of atactic concentration on G, one has to work with a wide gamut of iPP grades. The overall crystallization kinetics cannot be used to infer molecular information (on atactic content), because they are function of the previous (usually uncontrolled) thermo–mechanical history in the melt.

Bisupport for the olefin polymerization was prepared by the gelation of the colloidal phase of SiCO2 using MgCl2 solution as an initiator. The prepared Ziegler-Natta/Metallocene hybrid catalysts on the bisupport exhibited the characteristics of both Ziegler-Natta and metallocene catalysts. The polyethylene produced by the hybrid catalysts showed two melting temperatures and a bimodal MWD, suggesting that the polymer was composed of two different lamella structures that were polymerized by each catalyst.

Within the family of PE resins, linear low density PE (LLDPE) resins have found extensive applications in the areas of food packaging (for example, bakery, candy, frozen foods, ice-bags, etc.), non-food packaging (for example, garment bags, heavy duty sacks, stretch and shrink wrap, etc.) and non-packaging (for example, industrial can liners, agricultural films, medical, trash bags etc.). These numerous applications demand a vast range of application performance benefits that cannot be met by a single resin. A high molecular weight (M w ), broad molecular weight distribution (MWD) and often very low levels of long chain branching (LCB) typify chromium catalyst PE resins. Ziegler–Natta (Z–N) resins are typically narrower in MWD than chromium resins and contain no LCB. Metallocene resins are typically even narrower in MWD than Z–N resins and may or may not contain any LCB depending on the catalyst and process employed. Thus, it is clear that these three catalysts viz. chromium, Z–N and metallocene can yield PE resins with widely different molecular and rheological properties. This chapter examines the blown film processing–structure–property behavior and trade-offs with three different LLDPE resins from each catalyst mentioned.

Two metallocene catalyzed isotactic polypropylene, miPP, resins and a standard Ziegler-Natta isotactic polypropylene resin, zniPP, were melt spun into fibers. The fibers were spun under similar conditions to allow for direct comparison of fiber properties between the various resins. Two of the miPP resins differed by molecular weight, with a third miPP resin containing a nucleating agent. The fiber properties were found to be dependent upon molecular weight, MW, as has been previously documented.1 However, the tensile strengths of the metallocene resins were consistently higher in comparison with the conventional zniPP resin. The higher tensile strength can be attributed to the uniformity of the miPP chains in both length and in molecular microstructure that slightly retard crystallization and allow for a higher overall molecular orientation.

The crystallization behavior of three metallocene catalyzed isotactic polypropylenes were compared to that of a Ziegler-Natta catalyzed resin. The differences in behavior between the two type of resins are suggested to be a result of the differences in molecular microstructures of the resins. Characterization of the molecular microstructures suggest that the miPP resins have a more uniform defect distribution from chain to chain, compared to the zniPP resin.

According to the fact that very narrow molecular weight distributions (MWD) are easily produced with metallocene catalysts, the actual problems related to MWD are all concerned with wide distributions. Metallocene mixtures are able to produce bimodal distribution, requiring extreme differences in sensitivity to transfer reactions, but the expected properties will not be the same than those of wide peak distributions. The classical heterogenous systems produce sometimes broad to very broad distributions and this result is associated to a cluster structure of the transition metal. This cluster structure often forbids to mix 2 species to get the sum of 2 polymers. Examples combining titanium and vanadium chloride are presented. The effect of heat and monomer diffusion on MWD is generally not important.

Publisher Summary The heterogeneous Ziegler-Natta catalysts are a hard playground for kinetists and modelists. A molecular description of the kinetic behavior of such catalysts in 1-alkene polymerization requires to take into account the presence of several types of active sites and the extent to which, for each type of active sites, structural aspects affect the rate constants of chain propagation and transfer. The formidable advances, on the one hand, in the microstructural characterization of the polymerization products (mainly by CNMR) and, on the other, in the techniques of molecular mechanics, as applied to the evaluation of models of active centers, allowed a substantial progress in our understanding of the catalytic processes and in the rational development of better catalysts. The chapter presents an up-to-date presentation of the main results obtained from the experimental study of the regio- and stereospecificity of propene polymerization in the presence of the MgCl 2 -supported “high-yield” catalysts, which still monopolize the industrial production of isotactic polypropene.

Widely used radiotracer methods for active center determination, employing 14 CO tags and tritiated alcohol quench, generally provide conflicting results, thus casting doubt on the validity of both methods. This paper seeks to harmonize the apparent discrepancies by comparative studies on the polymerization of ethylene, propylene and 4-methylpent-1-ene, catalyzed by TiCl 3 .AA/AIR 3 , employing an innovative duel-labeling approach. It is concluded that quantitative 14 CO tagging of active site requires short contact times and high 14 CO concentrations to minimize interfering side reactions. The tritiated alcohol quench, after the tagging reaction, could provide information on the extent of transfer reaction. Under optimized conditions, tagging and quenching procedures can provide comparable and meaningful data.

This study investigates the possibility of modelling TiCl 3 Zeigler-Natta catalysts by building chloride layers on clean surfaces of Ti metal. The basal (0001) and lateral (10-10) surfaces were used to simulate the conventionally assumed inactive and poylerization-active surfaces of TiCl 3 . LEED and Auger data that a coincidence lattice of Cl forms on Ti (0001) which to some extent resembles the basal plane of TiCl 3 , while on Ti(10-10) chlorine atoms sit in the troughs. Olefins are decomposed by clean Ti, are are not adsorbed on fullt chlorided surfaces. On partially chlorided surfaces there are indications that some olefin may bond molecularly.

Titanacyclobutanes, catalysts for living ring opening metathesis polymerization (ROMP) of strained cyclic olefins, have been transformed into Ziegler-Natta catalysts. The synthetic routes that allow the transformation of 3,3-dimethylcyclopropene-titanacyclobutane 1, the most effective initiator of these ROMP polymerizations, and of trisubstituted titanacycles, such as 3, into the corresponding chlorine or ethoxy derivatives are reported. When trimethylaluminum is added to 1, 8 and 9 new alkylidene methyl-bridged bimetallic complexes, that can be considered as borderlines between metathesis and Ziegler-Natta catalysts, are obtained.

Publisher Summary In recent times, homo and copolymerization of ethylene are receiving considerable attention. Polyethylene is the world's most used polymer. This is because of various reasons, such as low linear density polyethylene (LLDPE) produced by copolymerization of ethylene with high α-olefins, such as 1-butene, 1-hexene, 1-octene, etc., is one of the most rapidly growing polymers; possibilities of producing different types of ethylene–propylene copolymers, such as random and block copolymers, etc. Among the catalytic systems used for homo and copolymerization of ethylene, metals supported on silica are indeed the leading catalysts in the polyolefin industry. Therefore, the huge amount of research works appearing in the technical and scientific literature is mainly concerned with this type of system. However, in spite of the efforts to understand how the SiO 2 features, such as surface area, pore volume, pore size distribution, etc., influence the polymerization activity and even resin properties, many questions are still open to discussion.

Highly active MgC1 2 - supported TiCl 4 Ziegler-Natta catalysts were used for propylene polymerization and the effect of varying the triethylaluminium concentration was studied in relation to the polymerization rate and to the number of active centres. Active centre concentrations were carried out using 14 C -labelled carbon monoxide. An optimum AlE 3 :Ti molar ratio was found to be necessary in order to obtain the highest rates of polymerization and the highest active centre concentrations. The concentration of active centres, C * , remains more or less constant with polymerization time, but the average propagation rate coefficient, κ p decreases. For AlEt 3 :Ti molar ratios greater than 80:1 values of both C * and κ p decrease only slightly with increase in AlE 3 :Ti molar ratio. Only 4.4–6.6 mol% of the total titanium was active. The dependence of the maximum values of the rates of polymerization on the alkylaluminium concentrations were investigated using Langmuir-Hinshelwood isotherms.

In this paper we will approach the study of the machanism of the Lewis base activation in high yield supported Ziegler-Natta catalysts by three different experimental routes: i) stereochemical study, by 13 C NMR analysis, of samples of polypropene prepared using selectively 13 C enriched AlEt 3 as cocatalyst; ii) GPC characterization of the most isotactic fractions; iii) study of the exchange between internal and external bases by GC analysis of the base content of the solid catalyst. Despite the well known complexity of the problem, on the basis of all these data it is possible to single out some general trends of the Lewis base activation and these trends depend more on the characteristics of the specific pair of internal and external bases than on those of the single internal or external base.

Internal Lewis bases (ILB) and external Lewis bases (ELB) are both necessary with the supported Ziegler-Natta catalysts to achieve the requirements of high activity and stereospecificity. The ILB is not directly involved in the active center. During the catalyst preparation the ILB masks the magnesium chloride surface, blocking the acidic defects. The catalyst is then formed by a selective replacement of the weakest bonded ILB by the titanium tetrachloride, giving thus access to low acidic active centers. The scheme can be considered as an active center selection. High activity is observed when a dynamic selection process results in an accumulation of trapped defects.

Publisher Summary This chapter points out that the behavior of molecular weight distributions (MWD) of polymers produced at the initial stages of polymerization, plays an important role for the mechanistic discussion of the broadness of MWDs. Supposing initial stages of polymerization where the yield and molecular sizes of produced polymers are very small, the original catalyst surface may remain unchanged and the diffusion control theory should predict a narrow MWD, because of the absence of any room to take the “multi-grain model” or “core model” of the diffusion control theory. The chain-length theory predicts the same conclusion. The nonuniform centers theory, however, predicts broad MWDs even for the initial stages of polymerization. Such initial polymerization stages appropriated for this criterion must belong to the quasi-living polymerization stage of any heterogeneous polymerization, where the average molecular size increases from a small and time-proportional value to a large stationary value. A few MWDs during quasi-living stages of heterogeneous Ziegler–Natta polymerization have been reported. The time dependency of MWDs reported are not unique but scatter, from a broader to a narrow, or vice versa, and down and up to stationary. Complex changes are assumed on the basis of changes in the number of some kinds of active centers. Thus, meaningful studies on MWDs in the course of quasi-living polymerization must be carried out together with observation of the kinetic behaviors of polymerization themselves. In this aspect, the experimental results described in the chapter are useful.

We describe here our results from a 13 C CP-MAS NMR and elemental analysis study of adsorption and interaction of a silyl ether, RSi(OMe) 3 (R = Ph), as an internal and an external electron donor with a MgCl 2 -supported Ziegler-Natta catalyst. A chemical activation of anhydrous MgCl 2 with EtOH and AlEt 3 produces a high surface area support stabilized by an organoaluminium compound, AlEt 2 (OEt). In a treatment of the thus obtained MgCl 2 with silyl ether the aluminium surface complex is retained and silyl ether is almost totally incorporated into the support. The effects of TiCl 4 and AlEt 3 treatments are also discussed.

Publisher Summary The kinetic studies on polymerizations using coordination catalysts present considerable difficulties owing to their complexity and variability, to the incomplete understanding of the reaction mechanisms, and to the problems in handling highly reactive and in many cases heterogeneous systems. It is essential, for a proper appreciation of the kinetics data, that there should be some knowledge of the catalyst structures and polymerization mechanism. Ziegler Natta catalysts exhibit great variations in catalyst stability and activity, and polymer yield varies greatly with different monomers. Ziegler-Natta polymerization kinetics are difficult to study experimentally, particularly those based on insoluble transition metal compounds. They are also complicated by the interaction of concurrent chemical reactions and by physical processes that may have either accelerating or retarding influences on the polymerization. The presence or absence of monomer during the preparation of Catalyst stoichiometry can have major effects; loss of activity is usually ascribed to decomposition of some organo-transition metal complex. Organo-transition metal compounds vary greatly in stability, but are frequently stabilized by complexation with other metal compounds and by adsorption on insoluble metal halides. The nature of the groupings attached to the metal may also have a pronounced influence on stability.

The historic development of polypropylene from its original discovery to the present is summarized, the economic impact of Natta's discovery is described and the main reasons for the exceptional development of polypropylene are given. The catalyst played an essential role in the successful development of the product; it is important that the principal research efforts were directed towards the study of the catalysts to achieve optimal product properties and process. On the basis of the possibilities of improving even further the process and developing new applicative opportunities for the product a very bright forecast for polypropylene is made.

The discovery of stereoregular polymers by Natta and his school has been the starting point of a series of researches aimed at connecting the chemical structure with the physical structure and properties of polymeric materials. Some recent and sometimes unexpected results of such researches, mainly in the field of the crystallography and conformational analysis of stereoregular polymers, are discussed in this paper.

The systematic preparation of supported Ziegler-Natta catalysts for ethylene polymerization was investigated. Catalysts were synthesized by a series of reactions of SiO 2 with TiCl 4 , AIR 3-x , Cl x , ZnEt 2 and RMgI compounds. The main co-catalysts used for activation were AlEt 2 Cl, AlEt 3 and Al(iso-Bu) 3 . Silicas Davison 951 and 952 having different surface areas, porosities and mechanical properties were employed as carriers. It could be shown that, for the catalysts prepared by simple impregnation of SiO 2 with TiCl 4 and by co-impregnation with TiCl 4 and AlEt 2 Cl, the carriers control the kinetic behavior of the catalysts. Thus, catalysts based on Davison 951 silica showed an acceleration type kinetic curve while those based on Davison 952 give a decay kinetic curve. Catalysts obtained by re-impregnation methods showed the highest activities when Al(iso-Bu) 3 was used for synthesis and for activation. In this case, the catalytical behavior is controlled by a layer of very active TiCl 3 , crystallite formed as a consequence of the large amount of TiCl 4 used. Catalysts with activities as high as 18.000 g. PE × g. Ti −1 × h. −1 × atm. −1 and having a good control of the polymer morphology could be obtained.

A mathematical procedure for the investigation of the lattice disorder by stacking faults in polycrystalline solids has been used in studying samples of MgCl2 activated by ball milling for various times in the presence of TiCl4. These samples have been investigated by X-ray diffraction and by measurements of surface area, crystallite dimensions, Ti content after washing and catalytic activity in the polymerization of ethylene. A good relationship has been confirmed between activation time and activity; furthermore, the structural variations introduced by ball milling are mainly associated with rotational disorder of the Cl-Mg-Cl triple layers. Nevertheless, the analysis by X-ray diffraction is not unequivocal about the relationships between structure and activity: other significant parameters, such as the surface area and the porosity, are probably very important.

Although our present fundamental understanding of Ziegler-Natta catalysis is one of the most advanced among the commercial catalysts, it is still far from perfect. Here, the kinetic approaches are critically summarized on the basis of a three-stage methodological classification system: characterization, phenomenological formalism and mechanistic approach. Under characterization the present conception of stereoregularity is criticized. In the second stage the proposed rate equations are discussed in light of experimental precision and kinetic models. The contradictions of our models with the experimental data found in studies on the effect of hydrogen on polymerization are pointed out, and the theories proposed for molecular weight distributions are discussed. Under mechanistic approach, the confusion in defining polymerization centers are pointed out. The definition suffers from both the definition in radical polymerizations and experimental operations. Reconsideration reveals some problems which remain unsolved and these are listed herein. Finally, an attempt is made to explain the effect of hydrogen on both polymerization rate and molecular weight.

The interaction between MgCl2, and electron donors and the structure of supported catalysts were studied by IR and XPS. Experimental data obtained demonstrated that the surface complexes between MgCl2 and electron donor probably formed during milling. When the catalysts were made by treating the milled product (MgCl2/PTP, MgCl2/PYRR) with TiCl4 a large quantity of PTP and PYRR came down from the support and TiCl4/PIP and TiCl4/PYRR complexes formed respectively, while the milled product was MgCl2/EB, the characteristic bands of MgCl2/EB in IR spectra were remained and this indicated that MgCl2/EB kept unchanged during the treating. When TiCl4EB complex was milled togetter with MgCl2, the complex decomposed and MgCl2/EB surface complex formed. The other component TiCl4 binds with MgCl2 through chlorine bridge. However, no exchange between the complex and MgCl2 support could be observed during the cogrinding of MgCl2 and TiCl4PIP or TiC142PYRR.

The award of the Nobel Prize for chemistry to Ziegler and Natta in 1963 was intended to acknowledge their revolutionary studies which had allowed them to obtain new polymeric materials with exceptionally controlled molecular structure and excellent properties. The polymerization catalyst they discovered and developed was indeed heterogeneous, and derived from the reaction of a transition metal compound, usually titanium tetra- or tri-chloride, and an alkylaluminum derivative.1,2 The heterogeneous structure, with crystaline titanium trichloride supporting the active species (coordinatively unsaturated alkyltitanium derivatives) on its surface, was from the beginning3 considered to be fundamental to ensuring good efficiency in the reaction. Moreover, it appeared necessary for the high linearity of ethylene polymers and the high isotactic stereoregularity of polypropylene and other 1-alkene polymers.4,5 Similarly, another catalytic system which acquired relevant industrial importance for producing polyethylene with high linearity was also heterogeneous, being based on chromium oxide supported over silica and/or alumina.6 Further generations of catalysts were also heterogeneous, up to the high activity systems supported on magnesium chloride presently used in industrial processes.7,8

The phenomenological behaviour shown by many Ziegler-Natta catalyst systems is outlined and the factors controlling the observed rate-time profiles are discussed in the light of existing kinetic models. Results for C* and derived values of kp are presented for the polymerization of propylene and 4-methylpentene-1 by MgCl2/EB/TiCl4-Al (i-Bu)3 catalysts. The concentrations and activities of polymerization centres giving rise to atactic and isotactic polymer in propylene polymerization are evaluated. The higher overall rates observed in both propylene and 4-methylpentene-1 polymerization are discussed in terms of C* and kp values. Increased values of C* obtained for higher α-olefin polymerization are also presented.