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Summary Diolefins can be used as comonomers in propylene copolymerizations in order to modify some of the final properties of the obtained poly(propylene) (PP) resins. Although reduction of catalyst activity can be expected when such copolymerizations are performed with standard heterogeneous Ziegler- Natta catalysts, copolymers containing 1,5-hexadiene (HD) and 1,7-octadiene (OD) can be produced at high rates when the comonomer content is sufficiently low (below 2 mol%); however, the presence of very small amounts of 5-ethylidene-2-norbornene (ENB) leads to complete catalyst inhibition. It is shown that incorporation of dienes lead to decrease of the melting point of the final product, especially in presence of ENB. When compared to HD, addition of OD causes more pronounced modification of the melt flow index and weight-average molecular weight, although the xylene solubles is less sensitive to the comonomer feed when the comonomer composition is low. Obtained results indicate that small amounts of dienes can be used at plant site to modify the final properties of PP resins produced with standard heterogeneous Ziegler-Natta polymerizations.

Summary Comprehensive polymer architectural studies were carried out on a group of Ziegler-Natta (Z-N) polyethylene homopolymers via size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) and rheology. Although Z-N resins are traditionally viewed as linear polymers, both SEC-MALS and rheology results strongly indicate that there are topological variations, presumably long-chain branching (LCB) or possibly hyper-branches, in this group of supposedly linear Z-N homopolymers. These Z-N homopolymers exhibit very complex elution behavior that resulted in anomalous elution profiles in SEC. It appeared that some high molecular weight (MW) and long-chain branched components followed a non-size exclusion separation mechanism on SEC columns, co-eluting with low MW and linear polyethylene components, causing a delayed elution. The possible origin of LCB in these Z-N polymers is also discussed.

Ziegler Natta (ZN) catalysts are used to produce a wide range of polyolefins on an industrial scale. It has long been known that polymer produced on these catalysts have a relatively wide distribution in chain lengths; values for the Poly-Dispersity Index (PDI) are generally well above 2, the value that would be expected if a single catalyst site type were active. These catalysts are conceptualised as containing a number of different active sites, which produce polymer with different average molecular weights. No physical explanation for the existence of different site types has been offered. In fact it has been shown that there is a close link between activity and oxidation state, and that only a single type of polymerising site is present. In this work, we propose that sites differ not in propagation rate but in the rate at which chain growth is terminated by a range of terminating agents, including hydrogen, monomer and co-monomer. Each terminating agent is considered to act at a particular “pseudo-site”. The ability of this interpretation to simulate a wide range of polymer properties is demonstrated. The pseudo-sites model is then used to investigate experimentally-determined chain length distribution data for ethylene-1-butene copolymer produced in lab reactors. It is shown that this new view of the heterogeneity of ZN active sites can successfully reproduce key polymer properties, including PDI and mean chain lengths. Based on these results, it is proposed that the pseudo-sites model can be used to consolidate experimental data into a single set of parameters to describe the behaviour of a Ziegler-Natta catalyst for polyolefin production.

In this work, an alternative formulation of the Population Balance Model (PBM) is proposed to simplify the mathematical structure of the reactor model. The method is based on the segregation approach applied to the recently developed unsteady state Residence Time Distribution (RTD). It is shown that the model can predict the performance of a reactor system under unsteady flow and composition conditions. Case studies involving time-varying catalyst flowrates, reactor temperature and reactor pressure were simulated and found to predict reactor performance with reasonable accuracy. The model was used to propose a grade transition strategy that could reduce transition time by as much as two hours.

Effects of external donor induced direct contact without alkylaluminum were studied for Ziegler-Natta catalysts containing monoester and diester as internal donors on the catalytic performances such as activity and stereoselectivity. Traditional slurry polymerizations were carried out for rather short period after direct contact for a variety of time. GC analysis was also performed to observe replacement phenomena of donors during direct contact. It was postulated that the different performances of the catalysts were greatly affected by the pair of internal and external donors.

Heterogeneous Ziegler-Natta catalysts are still the most important catalysts for the industrial production of polyolefins, despite the discovery of high-activity metallocene systems in the eighties. Despite of their huge commercial importance, several aspects of Ziegler-Natta catalysts are still poorly understood from both qualitative and quantitative points of view. Especially for polypropylene, a very important factor controlling product quality is the effect of the electron donor used to modify the catalyst. In this manuscript we present, for the first time, a quantitative mathematical model that describes the effect of electron donors on the tacticity of polypropylene made with multiple-site type catalysts.

Heterogeneous Ziegler-Natta catalysts produce polyolefins that have broad distributions of molecular weight (MWD) and chemical composition (CCD). For such broad distributions, mathematical models are useful to quantify the information provided by polyolefin analytical techniques such as high-temperature gel permeation chromatography (GPC), temperature rising elution fractionation (TREF), and crystallization analysis fractionation (CRYSTAF). In this paper, we developed a mathematical model to deconvolute the MWD and CCD of polyolefins simultaneously, using Flory's most probable distribution and the cumulative CCD component of Stockmayer's distribution. We have applied this procedure to "model" polyolefin resins and to one industrial linear low-density polyethylene (LLDPE) resin. The proposed methodology is able to deconvolute theoretical distributions even when random noise is added to the MWDs and CCDs, and it can be used to calculate the minimum number of active site types on heterogeneous Ziegler-Natta catalysts.

Heterogeneity of active centers (AC) of titanium-magnesium catalysts (TMC) and vanadium-magnesium catalyst (VMC) in ethylene-hexene-1 copolymerization has been studied on the base of data of polymer molecular weight distribution (MWD) deconvolution technique and copolymer fractionation onto narrow fractions. It was found that 3 and 4 Flory components (groups of active centers) are required to describe experimental MWD curves of copolymers produced over TMC with different Ti content. In the case of VMC MWD of homopolymer and copolymer are characterized by set of 5 Flory components (5 groups of AC). Different character of inter-relationship between MW and short chain branching (SCB) was found for ethylene-hexene-1 copolymers produced over different catalysts: heterogeneous type in the case of TMC and more uniform for copolymer prepared over VMC. The content of Ti affects on the slope of that profile in copolymers produced over TMC. The results indicated that TMC and VMC are different greatly on the heterogeneity of active centers to the formation of polymers with different molecular weights and to formation of copolymers with different inter-relationship between MW and short chain branching. TMC produces polymers with more narrow MWD but it contains highly heterogeneous centers regarding comonomer reactivity ratios. VMC produces polymers with broad and bimodal MWD but it contains more homogeneous centers regarding comonomer reactivity ratios.

In this work, a combination of experimental and computational approaches on the isospecific role of monoester-type internal electron donors (ED) such as phenylpropionate (PhP), ethylheptanoate (EH), methylbenzoate (MB), ethylbenzoate (EB) for TiCl 4 /ED/MgCl 2 Ziegler-Natta catalysts had been performed. The propylene polymerization results revealed that the isospecificity of catalysts increases in the following order: PhP< EH < MB< EB. The subsequent molecular modeling on the electronic properties of the donors and two kinds of cluster model catalysts: TiCl 4 /ED/MgCl 2 and TiCl 4 /ED/(MgCl 2 ) 4 based on density functional theory (DFT) method was carried out. Two kinds of ED coordination on MgCl 2 clusters through either =O or -O- within the monoester-type ED had been disclosed. A perfect correlation between the dipole moment of ED, the coordination bond length of =O... Mg, the competitive coordination from -O- with Mg ion and the isospecificity of the catalysts had been established.

All polymerization experiments were carried out in a Buchi glass reactor capable of operating at propylene pressures of 1-7 atmospheres. Two types of MgCl 2 supported catalysts with controlled morphology were studied, viz., catalyst systems containing either a 1,3 diether (Catalysts A and D), 9,9-bis (methoxymethyl) fluorene, or a simple diester (Catalysts B, C and E) such as diisobutylphthalate, used as reference systems. The kinetic behaviours of these catalysts were investigated for propylene polymerization. The 1,3-diether based systems proved to be excellent catalyst systems for propylene polymerization showing high polymerization activities and stable rate-time profiles and produced spherical polymer particles. Catalyst pre-treatment was found to play an important role in controlling the morphology of the final polymer. A tritiated alcohol radio-quenching technique was used to determine the concentrations active centres: values of 7.5 and 5.1 mol/mol % respectively were obtained for catalysts A and D and 3.5, 2.9 and 2.2 mol/mol % respectively were obtained for catalysts B, C and E. Catalysts A and D showed very high polymerization activities and also higher C o * values. All polymers produced were characterized by SEM, DSC, extraction and molecular weight determinations.

Polypropylene was produced in gas phase and liquid phase using different supported Ziegler-Natta-catalysts. Sorption behaviour of propylene in polymer particles was studied gravimetrically. The analyzed polymer fractions have average diameters between 250 and 875 μm. Generally it was found that the effective diffusion coefficient is increasing with increasing size of polymer particles. With electron microscopy a change of polymer particle morphology with particle size and type of catalysts was observed.

Based on the recent literature, the synthesis of novel polyolefin architectures via Ziegler-Natta chemistry under living conditions appears to be a promising and fast-growing area. In this paper, the appropriateness of the term living as applied to the said context is discussed in mechanistic terms, and the potential and the limitations of the field are outlined with the aid of two paradigmatic case histories (i.e., propene polymerization in the presence of bis(phenoxy-imine)Ti and bis(phenoxy-amine)Zr catalysts).

A first principles molecular dynamics study of various active surfaces and Ti catalytic sites is presented. We first review some of our recent results about MgCl 2 lateral cuts acting as a support for Ti catalytic sites and inspect the structure and stability of the standard binuclear model. We find that catalytic adducts TiCl 4 and Ti 2 Cl 6 , which are the standard precursors of the active catalytic system, can bind more or less efficiently to the support according to the morphology of the active surfaces. Furthermore, the activation and polymerization phases are shown to be critical in determining whether or not a particular site is stable and suitable to carry out the polymerization process. We also address the problem of regioselectivity. Finally, we have attempted for the first time a first principles study of the role of a typical donor phthalate elucidating its binding properties on the different substrate cuts and its behavior as a poisoning agent for the Corradini mononuclear active site. These studies are very preliminary.

The MgCl 2 supported half titanocenes and Ti(4,4,4-trifluoro-1-phenyl-1,3-butanedionato) 2 Cl 2 catalysts were synthesized and applied to propene polymerization. Without supporting on MgCl 2 , those complexes displayed almost no activity even using methylaluminoxane (MAO) as cocatalyst. When supported on MgCl 2 , on the other hand, the resulting catalysts could be activated by ordinary alkylaluminums to yield polypropene in fairly high yields. The catalyst isospecificity was markedly improved by the addition of a suitable Lewis base.

Giulio Natta was a man strongly involved from an emotional viewpoint in his research activity, and in that sort of reflections he was so absorbed as to give the impression that he was living in his own world. Nevertheless, in spite of the enormous amount of work he was carrying on virtually day and night through study, writing of his own papers and uninterrupted reflection, he was a man of a vast culture in Natural Sciences, especially Mineralogy and Botany. Besides, until allowed by his health, he loved to live in the open air and, especially, mountain excursions. He could manifest much sympathy and personal involvement to the people close to him, as I may witness myself for the thirteen years I was one of his coworkers. On the whole, in spite of his absorbed and somewhat shy appearance, he was a man who deeply loved life.

The results of a study on a new generation of MgCl2 supported Ziegler-Natta catalysts that contain dialkyl propane diethers as internal donors and produce highly stereospecific polypropene even without any external donor are presented. The results concerning three different catalysts containing 2,2-diisobutyl-1,3-dimethoxy propane (DIBDMP), 2,2-dicyclopentyl-1,3-dimethoxy propane (DCPDMP) and 2-ethyl,2-butyl-1,3-dimethoxy propane (EBDMP) as internal donors are compared. The same donors have also been studied by using them as external donors with a catalyst contaning diisobutyl phthalate as internal donor. The present results, along with previously obtained findings on traditional supported Ziegler-Natta catalysts, permit a general comprehension of the role of internal and external donors.

The interest for the stereospecific polymerization of olefins discovered by prof. Natta in 1954 was so high that only a few years elapsed between the discovery and the commercialization of polypropylene. The polypropylene discovery generated a tremendous scientific and technological effort for the development of the catalyst, the process, the products. The fundamental achievements in the polypropylene technology had a significant impact over the polyolefin technology in general. Thanks to it, polyolefinic polymers, copolymers and rubbers, polyefinic based materials and alloys via heterogeneous Ziegler-Natta catalyst polymerization are today largerly the most important family of plastic materials. The ability to vary melt flow and the broad properties range of these materials, the excellent thermal and physical-mechanical properties of isotactic polyolefins together with the favorable economics and their full and easy recyclability widen the concept of monomaterial application fuelling their dynamic expansion since the early sixties.

The paper recalls some aspects of the fascinating history of the discovery by Giulio Natta and his coworkers of the stereospecific polymerization of α-olefins and of the determination of the structure of synthetic stereoregular polymers. The most relevant recent advances in the comprehension of the mechanisms regulating their synthesis with heterogeneous supported catalysts and with the newly discovered homogeneous metallocene-based catalysts are briefly outlined.

The formulae for conditional probabilities are derived with the term of NMR triad tacticities for the polymers whose polymerization process is described by an asymmetric Markovian process. The formulae obtained are applied to the polypropylene polymerized by Ziegler-Natta catalysis with external alkoxysilane donors. For both, unfractionated samples and heptane-insoluble fractions, four evidences are clarified as follows: Don the transformation from symmetric to (fluctuating) asymmetric sites the transformation of one (hereafter, L) site is much more enhanced than that of the other (D) site, 2) monotonous increase of isotacticity with an increase of the concentration of the donor is due to the increase of pLL, 3) aromatic donors are more effective than aliphatic ones for the improvement of isotacticity, and 4) the improvement of isotacticity after an addition of alkoxysilane is not due to the contribution from both of L and D sites, but the competition between the larger positive contribution from the former and the smaller negative one from the latter.

Forty years after Natta's discoveries of stereospecific olefin polymerization with Ziegler catalysts, new catalysts are causing a renaissance in stereospecific olefin polymerization. Metallocene Ziegler-Natta catalysts are unprecedented in their ability to polymerize α-olefins to a variety of polymer microstructures.1 Isotactic, syndiotactic, atactic and stereoblock poly(α-olefins) have been produced using catalysts derived from group 4 metallocene catalyst precursors.