Polyethylenimines, polymers bearing amino functionalities, are studied for the first time as internal electron donors for Ziegler-Natta catalysts. An advantage of polyethylenimines (PEIs) compared to the conventional phthalate electron donors is their relative harmlessness. Interaction of PEI with MgCl2 support was studied using computational (DFT; M06-2X) and experimental (PXRD, DRIFT, CP/MAS C-13 NMR) methods. Quantum chemical calculations suggest that the structural variations in PEIs significantly affect their ability to stabilize the catalytically relevant MgCl2 surfaces. Coordination on the (104) surface seems to be favored upon consideration of the layered structure of MgCl2. The surface stabilization energies of branched PEIs are of the same magnitude with a phthalate electron donor reference. Experimental results indicate, in agreement with theoretical results, a strong coordination ability of branched PEI through nitrogen atoms to MgCl2. Based on spectroscopic data, nitrogen atoms of primary, secondary, and tertiary amino groups can participate in coordination to MgCl2. Calculations indicate that the strongest coordination of branched PEI occurs through primary amino groups. A Ziegler-Natta catalyst containing branched PEI as an internal electron donor (MgCl2/PEI/TiCl4]) showed a reasonably high activity in ethylene/1-butene copolymerization. Overall, the combined computational and experimental results provide detailed information about coordination of nitrogen-containing polymeric electron donors to MgCl2 support and indicate their potential as a new type of internal electron donors for Ziegler-Natta catalysts.

Ziegler-Natta polymerization catalysts were characterized by a complex of surface-and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti4+, Ti3+, Ti2+, and Ti1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom.

We report the first quantum chemical description of the initial steps of Ziegler-Natta olefin polymerization catalysis involving all the relevant catalyst components. TiCl4 binds on the (1 0 4) surface of MgCl2 as a binuclear Ti2Cl8 and on the (1 1 0) surface as a mononuclear TiCl4, both binding modes being stabilized by octahedral six-coordination of Ti and Mg. Aluminum alkyl (triethylaluminum) coordinates to the MgCl2 surface via an unsaturated Cl to initiate catalyst alkylation reactions, thermodynamically driven by dimerization of the chlorinated aluminum alkyl. Addition of an internal donor (dimethyl phthalate) greatly stabilizes the (1 0 4) and (1 1 0) surfaces, ending up directing the alkylation reactions to the binuclear (1 0 4) site. External donor (dimethoxydimethylsilane) further assists the process, stabilizing similarly both catalytic surfaces. The spatial requirements of the donors are shown to be greater on the (1 1 0) surface than on the (1 04) surface, rationalizing the role of Lewis bases in the stereocontrol of polyolefins. (C) 2017 Elsevier Inc. All rights reserved.

We evaluate the stabilization of magnesium dichloride surfaces by mono- and bidentate electron donors typically used in heterogeneous Ziegler–Natta olefin polymerization catalysis: tetrahydrofuran, ethyl benzoate, 2,2-dimethyl 1,3-dimethoxy propane, 2S,2R-di(2-tetrahydrofuryl) propane, dimethyl phthalate, and dimethyl succinate. Structural defects are generated into the ideal (104) and (110) MgCl2 surfaces, and both ideal and defective surfaces are saturated by the donors. The quantum chemical calculations (PBE0 density functional theory method), performed with periodic boundary conditions, show that all donors stabilize all surfaces. Stabilization energy of the surfaces by the ethers is linearly dependent on surface site coordination, the four-coordinate (110) surface being stabilized the most, the five-coordinate (104) surface the least, and all the defective structure fitting in between the two limiting cases of the ideal surfaces. However, the esters can additionally stabilize the defective surfaces depending on the steric effects at the point of coordination. The results suggest that defects need to be taken into account to properly address the surface–donor complexation.

The present invention relates to a propylene homopolymer with reduced emission value and high melt flow rate. The object of the present invention provides a polymer material which is rather stiff and characterized by low emissions. The finding of the present invention is that a propylene homopolymer must be produced with a Ziegler-Natta catalyst containing an internal donor (ID) not belonging to the class of phthalic acid esters. With such a catalyst propylene homopolymer can be produced having excellent stiffness and low emission values.

Coadsorption of titanium tetrachloride and two representative bidentate electron donors on magnesium dichloride surfaces is systematically studied by means of periodic quantum chemical calculations. The two catalytically relevant surfaces in the ZieglerNatta catalysis, (104) and (110) surfaces of the MgCl2 support, are taken into account. Adsorption of TiCl4 leads to formation of three types of mononuclear species on the magnesium dichloride surfaces. However, TiCl4 alone cannot properly stabilize the support. Coadsorption of electron donors along with TiCl4, on the other hand, is shown to significantly improve the strength of TiCl4 adsorption on the magnesium dichloride surfaces. Our findings indicate the importance of electron donors as promoters of titanium tetrachloride adsorption. The model is readily extendable to evaluate other electron donors and binuclear titanium species.

We describe a concept for modeling structural defects in crystalline magnesium dichloride used as a support in the Ziegler–Natta polymerization catalysis. The defects are systematically generated into the catalytically relevant (104) and (110) MgCl2 surfaces and stabilized by methanol, selected as a model electron donor. Periodic quantum chemical calculations indicate a strong effect of surface site coordination on the relative stabilities of both ideal and defect surfaces, favoring sites with five-coordinate magnesiums. Saturation of the surfaces by the donor completely reverses the stability order in comparison to the plain surfaces, ending up favoring four-coordinate magnesium atoms. The approach can be readily expanded to include more complex donors as well as titanium chlorides.

In this study, solid state (13)C NMR spectroscopy was utilised to characterize and identify the metal-ester coordination in active fourth generation (phthalate) Ziegler-Natta catalysts. It is known that different donors affect the active species in ZN catalysts. However, there is still limited data available of detailed molecular information how the donors and the active species are interplaying. One of the main goals of this work was to get better insight into the interactions of donor and active species. Based on the anisotropy tensor values (δ(11), δ(22), δ(33)) from low magic-angle spinning (MAS) (13)C NMR spectra in combination with chemical shift anisotropy (CSA) calculations (δ(aniso) and η), both the coordinative metal (Mg/Ti) and the symmetry of this interaction between metal and the internal donor in the active catalyst (MgCl(2)/TiCl(4)/electron donor) system could be identified.

We evaluate methods and models for the periodic quantum chemical treatment of defects in MgCl2 polymerization catalyst support and demonstrate the applicability of the approach for a study of chemical substitution of chlorine with bromine. Effects of the defects are evaluated through binding of methanol to catalytically relevant MgCl2 surfaces. Our results show that the hybrid density functional PBEO method reproduces the MgCl2 crystal structure in good agreement with experiments and that a triple-zeta quality basis set is required to evaluate the donor binding properties. Furthermore, the effects of the defects depend on their position in the crystal lattice, and destabilization of the crystal lattice results in increased donor binding energy. Therefore, substitutions at the coordinatively unsaturated edges typically stabilize the crystallites and lower the donor binding energies, whereas substitutions at the coordinatively saturated bulk typically destabilize the crystallites and increase the donor binding energies. The effects are stronger on the (104) than on the (110) surface. The study is readily extendable to other kinds of defects occurring in crystallites.

The ability to control the microstructure of magnesium dichloride (MgCl2) crystallites by electron donors was demonstrated by quantum chemical calculations, using methanol as a model donor. Investigation of sets of differently shaped MgCl2 crystallites showed the dominance of the five-fold coordinated (100) crystal surface over the four-fold coordinated (110) surface to emerge as a factor increasing crystallite stability. To study the role of electron donors in controlling MgCl2 crystallite shape, crystallites were saturated with methanol. The stability order of the crystallites was significantly affected by donor adsorption. Reverse to the case of pure MgCl2, crystallites with the highest (110) to (100) surface site ratio became the most stable after donor adsorption. This indicates control of the shape of MgCl2 crystallites to be attainable by appropriate choice of electron donor, a result utilizable in heterogeneous Ziegler–Natta olefin polymerization catalysis.

Complex formation of MgCl2 with 2-(2-ethylhexyloxy)ethanol was studied by IR and NMR spectroscopic methods and molecular modeling to determine the binding mode of the alcohol to MgCl2. According to both experimental and theoretical studies, during the reaction of the alcohol and MgCl2, two alcohol molecules form an adduct with MgCl2 through the oxygen atoms of the alcohol and ether groups, giving rise to a chelated structure. Crystallization of the MgCl2/2-(2-ethylhexyloxy)ethanol complex was attempted by various methods. Toluene was used as solvent in the dissolution of MgCl2 in alcohol, and heptane was used to adjust the solubility of MgCl2 during the crystallization. Crystals piled up as thin plates. Single-crystal X-ray structure analysis revealed a chelated structure formed through the oxygen atoms of the ether and alcohol groups. Two water molecules are also bound to the magnesium, as seen in the IR spectrum of the crystals as well.

Particle growth and fragmentation of solid Ziegler–Natta-type catalysts prepared via emulsion technique were studied in propylene polymerization. Before polymerizations the catalyst particles were activated with triethyl aluminum (TEA) and cyclohexyl methyl dimethoxy silane (CMMS). Polymerizations were carried out in gas-phase in a micro-reactor system that allows the particle growth to be observed with a microscope. Several polymerizations were done under a propylene pressure of 2bar and with polymerization times from 20s to 2h. Fragmentation morphology of the catalyst particles and cross-sections of the particles after polymerization were studied by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Fragmentation morphology of the catalysts prepared via emulsion technique was compared with the fragmentation morphology of a conventional MgCl2-supported Ziegler–Natta-type catalyst, which could be described by the multigrain model. Polymer growth appeared to occur throughout the emulsion-based catalyst particle right from the start of the polymerization, even though the surface area and porosity of the catalyst were low. The surface of the catalyst particles broke up at the beginning of the polymerization, and catalyst fragments appeared on the surface as plates between which the polymer was growing.