Internal Donor Research Articles

Structure of Donor Molecule 9,9-Bis(Methoxymethyl)-Fluorene in Ziegler-Natta Catalyst by Infrared Spectroscopy and Quantum Chemical Calculation

Infrared vibrational spectroscopy has been used to reveal the conformations of the Ziegler−Natta catalysts internal electron donor 9,9-bis(methoxymethyl)-fluorene and its selectively deuterated derivative (9,9-bis(1,1-dideutero-methoxymethyl)-fluorene), in the solid state, complexed with TiCl4 and MgCl2 and in the catalyst precursor. The experimental spectra have been interpreted by means of spectroscopic correlations and theoretical results from quantum chemical calculations on selected molecular models. From experimental and theoretical data two chelating geometries of the donors with both oxygen directly interacting with Ti or Mg atoms turn out to be favorable. They can be identified by the four dihedral angles along the CH3−(O−CH2−R−CH2−O)−CH3 residue that take on conformations of approximately trans (T), gauche+ (G), or gauche− (G′), namely, TGGT and TGG′T. We propose the TGGT conformations for the crystal phase of the donor, the TGG′T when it is complexed with TiCl4, and both TGGT and TGG′T when complexed with MgCl2 along the [110] lateral cut. In the precatalysts, donors molecules are complexed along the [110] MgCl2 lateral cut and likewise the MgCl2 complex. A model for the catalytic sites consisting of TiCl4 species and donor molecules complexed along the [110] lateral cut is proposed.

Preparation of ultra high molecular weight polyethylene with MgCl2/TiCl4 catalyst: effect of internal and external donor on molecular weight and molecular weight distribution

Ultra high molecular weight polyethylene (UHMWPE) was prepared by using MgCl2-supported TiCl4 catalyst in conjunction with triethylaluminium (TEA) cocatalyst. The effects of internal and external donor on polydispersity index (PDI) of UHMWPE were investigated. The catalyst activity with various kinds of internal donor decreased in the following order: none > succinate > phthalate > diether, while the catalyst activity was less influenced by the structure of external donor. The PDI of UHMWPE was examined by using gel permeation chromatography (GPC) analysis and/or rheometry measurements. The PDI obtained by rheometer was matched with the results obtained by GPC within an error of max. 20%. The highest molecular weight and PDI of UHMWPE were obtained by the catalyst of succinate as internal donor. It was also observed that the molecular weight and PDI of UHMWPE were less affected by the introduction of external donor.

Modifications of the active sites distribution in the Ziegler-Natta polymerization of propylene using Lewis acids

Heterogeneous Ziegler-Natta precatalysts (with phthalate as internal donor) were modified by treatments with various Lewis acids (MCln with M = Ga, Sn, Si, and Sb and n = 3, 4, or 5) before their use in the polymerization of propylene. If performed on previously “detitanated” precatalysts, treatments with SnCl4 and SiCl4 lead to a slight activation but especially to an increase of the tacticity whereas GaCl3 and SbCl5 treatments deactivate the catalyst. The modification method applied to conventional unmodified precatalysts gave similar trends. A significant increase of tacticity (and/or of Tm) and a narrowing of the molecular weight distribution were observed in the case of SnCl4 and SiCl4 treatments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2631–2635, 2010

Low-Temperature FTIR Study of Gloeobacter Rhodopsin: Presence of Strongly Hydrogen-Bonded Water and Long-Range Structural Protein Perturbation upon Retinal Photoisomerization

Gloeobacter rhodopsin (GR) is a light-driven proton-pump protein similar to bacteriorhodopsin (BR), found in Gloeobacter violaceus PCC 7421, a primitive cyanobacterium. In this paper, structural changes of GR following retinal photoisomerization are studied by means of low-temperature Fourier-transform infrared (FTIR) spectroscopy. The initial motivation was to test our hypothesis that proton-pumping rhodopsins possess strongly hydrogen-bonded water molecules in the active center. Water O-D stretching vibrations at <2400 cm(-1) in D(2)O have been regarded as coming from such strongly hydrogen-bonded water, and there is a strong correlation between the proton-pumping activity and the presence of such water molecule. Since GR pumps protons, we expected that GR also possesses strongly hydrogen-bonded water molecule(s), and the FTIR results clearly show that this is indeed the case. In addition, another unexpected finding was gained from the frequency region of protonated carboxylic acids in the GR(K) minus GR spectra at 77 K, where we observed the unique bands of a protonated carboxylic acid at 1735 (+)/1730 (-) cm(-1). Comprehensive mutation study revealed that the vibrational bands originate from the carboxylic C=O stretch of Glu132 at the position corresponding to Asp96 in BR. Glu132 presumably functions as an internal proton donor for the retinal Schiff base, but they may be located far apart (ca. 12 A in BR). The present study demonstrates the long-range structural changes of GR along the proton pathway, even though the protein matrix is frozen at 77 K.

Synthesis of polypropylene with varied microstructure and molecular weights characteristics using supported titanium catalyst system

Propylene polymerizations were conducted in slurry phase batch process using different dialkyldimethoxysilanes as an external donor with magnesium dichloride (MgCl2) supported titanium tetrachloride (TiCl4) catalyst having diisobutylphthalate (DIBP) as an internal donor. The dialkyl group of the external donors like dimethyldimethoxysilane (DMDMS), diisopropyldimethoxysilane (DIPDMS) and dicyclopentyldimethoxysilane (DCPDMS) were found to influence on the microstructure and the molecular weight characteristics of synthesized polypropylene in addition to the initial rate of polymerization and decay index. DCPDMS gave highest productivity and high molecular weight polypropylene with improved kinetics while DMDMS gave lowest productivity in comparison. The molar equivalent combination of DCPDMS with DIPDMS and DMDMS respectively, resulted in producing polypropylene with tacticity pattern and molecular weight characteristics in between the individual alkoxysilane based system indicating the effect of alkyl group on the catalyst performance.

THE STRUCTURE AND MORPHOLOGY CHARACTERS OF PP/EPR &lt;I&gt;in situ&lt;/I&gt; BLENDS SEQUENTIALLY PREPARED BY ZIEGLER-NATTA CATALYST

PP/EPR in situ blends were prepared by the sequential polymerization technique using a Ziegler-Natta catalyst MgCl_2/TiCl_4/BMF(BMF is 9,9-bis(methoxymethyl)fluorine as an internal donor).The content of ethylene unit in blends was adjusted by modifying the time of ethylene-propylene copolymerization.The structure and morphology characters of the blends obtained were investigated by nuclear magnetic resonance(NMR),gel permeation chromatography(GPC),dynamic mechanical analysis(DMA),differential scanning calorimetry(DSC),scanning electron microscopy(SEM) and polarized light microscopy(PLM).The results suggested that PP/EPR is a complex multiphase mixture including PP,EPR and EP block copolymer.The presence of EP block copolymer greatly improved the compatibility between the PP matrix and the EPR dispersed phase in the multiphase system.The compatibility between the PP matrix and the EPR dispeersed phase in the multiphase system.The change of the ethylene unit content in PP/EPR remarkably influenced the crystalline morphology of PP with increasing the content of ethylene unit in the blend,the PP spherulites became smaller and irregular.

A pathogenic mutation in cytochrome c oxidase results in impaired proton pumping while retaining O 2-reduction activity

In this work we have investigated the effect of a pathogenic mitochondrial DNA mutation found in human colon cells, at a functional-molecular level. The mutation results in the amino-acid substitution Tyr19His in subunit I of the human Cyt cO and it is associated with respiratory deficiency. It was introduced into Rhodobacter sphaeroides, which carries a cytochrome c oxidase (cytochrome aa 3) that serves as a model of the mitochondrial counterpart. The residue is situated in the middle of a pathway that is used to transfer substrate protons as well as protons that are pumped across the membrane. The Tyr33His (equivalent residue in the bacterial Cyt cO) structural variant of the enzyme was purified and its function was investigated. The results show that in the structurally altered Cyt cO the activity decreased due to slowed proton transfer; proton transfer from an internal proton donor, the highly-conserved Glu286, to the catalytic site was slowed by a factor of ∼ 5, while reprotonation of the Glu from solution was slowed by a factor of ∼ 40. In addition, in the structural variant proton pumping was completely impaired. These results are explained in terms of introduction of a barrier for proton transfer through the D pathway and changes in the coordination of water molecules surrounding the Glu286 residue. The study offers an explanation, at the molecular level, to the link between a specific amino-acid substitution and a pathogenic phenotype identified in human colon cells.

A stacked neural network approach for yield prediction of propylene polymerization

AbstractPrediction of reaction yield as the most important characteristic process of a slurry polymerization industrial process of propylene has been carried out. Stacked neural network as an effective method for modeling of inherently complex and nonlinear systems–especially a system with a limited number of experimental data points–was chosen for yield prediction. Also, effect of operational parameters on propylene polymerization yield was modeled by the use of this method. The catalyst system was Mg(OEt)2/DIBP/TiCl4/PTES/AlEt3, where Mg(OEt)2, DIBP (diisobutyl phthalate), TiCl4, PTES (phenyl triethoxy silane), and triethyl aluminum (AlEt3) (TEAl) were employed as support, internal electron donor (ID), catalyst precursor, external electron donor (ED), and co‐catalyst, respectively. The experimental results confirmed the validity of the proposed model. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation of MgCl 2-supported Ziegler–Natta catalyst systems with new electron donors

In the present work, the effect of new internal and external electron donors for Ziegler–Natta systems of the type MgCl 2/DI/TiCl 4/DE/AlR 3 was compared with the conventional use of n-butyl phthalate and dimethoxy-diphenylsilane as electron donors. Catalyst systems employing various internal and external donors were evaluated in propylene polymerization. The polymers were characterized by infrared absorption spectroscopy, differential scanning calorimetry and heptane extraction. The prepared catalysts with the new internal donors produced polypropylene with isotactic index up to 98% under the polymerization conditions employed.

DRIFTS study of the interaction of the internal donor in TiCl 4/di-n-butyl phthalate/MgCl 2 catalysts with AlEt 3 cocatalyst

The interaction of di-n-butyl phthalate (DBP as the internal donor) with AlEt 3 cocatalyst was studied by DRIFT spectroscopy for the DBP/MgCl 2 sample and supported TiCl 4/DBP/MgCl 2 catalysts. For DBP/MgCl 2 sample, it was shown that AlEt 3 partially removes all types of DBP complexes from the MgCl 2 surface and adsorbs on surface sites released by the removal of DBP. In the case of supported catalysts, the cocatalyst predominantly removes more weak DBP complexes. In addition, the cocatalyst completely removes loosely coordinated DBP and surface complexes of phthaloyl chlorides formed at the catalyst preparation. A part of removed DBP can adsorb again on the catalyst surface as complexes with surface alkylaluminum chloride compounds. The external donor alkylalkoxysilane does not markedly influence the removal of DBP complexes from the catalyst surface.

External Donor Induced Direct Contact Effects on Mg(OC2H5)2‐Based Ziegler‐Natta Catalysts for Propylene Polymerization

AbstractEffects 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.

Strong activation of MgCl2 -supported Ziegler-Natta catalysts by treatments with BCl3 : Evidence and application of the “cluster” model of active sites

Heterogeneous Ziegler-Natta precatalysts (with phthalate as internal donor) were modified by treatments with BCl3 (2 h in heptane; T = 20–90 °C; B/Ti = 0.1–5) before their use in the polymerization of propylene to modify the active sites distribution. If performed on previously “detitanated” precatalysts, the treatment leads to a strong increase of productivity (up to one order of magnitude) without drastic modifications of polypropylenes properties (tacticity, molecular weight distribution). In addition, these findings are in good agreement with the hypothesis of a “cluster” organization of active sites allowing to rationalize activation by BCl3 by formation of heteronuclear B-Ti clusters. The activation method was also applied to unmodified precatalysts and gave a significant gain of productivity. The simple and versatile activation process can also be performed under mild conditions (low T and low [BCl3]). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5784–5791, 2009

Poly(1‐octene) synthesis using high performance supported titanium catalysts

AbstractPoly(1‐octene) was synthesized by polymerization of 1‐octene using high performance MgCl2‐supported TiCl4 in combination with triethyl aluminum (TEAl) as cocatalyst in n‐hexane for 2 h. Two catalysts, C1 (diester catalyst) having di‐isobutyl phthalate as internal donor and C2 (monoester catalyst) having ethyl benzoate as internal donor were utilized for the atmospheric polymerizations to evaluate the influence of structurally different internal donors on the productivity, rate of polymerization and molecular weight profiles. The kinetic profile assessed in terms of variation of reaction parameters like temperature, cocatalyst to catalyst molar ratio and monomer concentration was found to be dependent on them. From these kinetic analyses, optimize conditions for polymerizations of 1‐octene using diester as well as monoester catalyst were elucidated. The difference in the performance of diester and monoester catalyst system can be explained in terms of stability of active titanium species and chain transfer process. NMR spectroscopy of synthesized poly(1‐octene) indicate predominantly isotactic nature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Stereo- and enantioselective polymerization of hexa-1,5-diene on heterogeneous Ziegler-Natta catalysts obtained with the use of optically active internal donors

Pure racemates and individual enantiomers of diethyl 2,3-diisopropylsuccinate ((+,−)-DIPS and (−)-DIPS) and 2,3-diisopropyl-1,4-dimethoxybutane ((+,−)-DPDMB and (+)-DPDMB) were prepared. The synthesized compounds and diethyl phthalate were used as internal donors for the preparation of heterogeneous Ziegler-Natta catalysts. Polymerization of hexa-1,5-diene was carried out on these catalysts. The obtained samples of poly(methylene-1,3-cyclopentane) were studied by 13C NMR spectroscopy and polarimetry. The induction of optical activity to polymer is observed with (−)-DIPS as the internal donor. The induction value makes up 15–20% from the value recorded in the case of optically active metallocene catalysts. The emergence of induction may be associated with the presence of close contact between the titanium atom and the donor molecule within the active site of catalyst, as well as with the fact that the donor molecule either deactivates a part of the stereospecific titanium centers or influences the structure of the titanium centers during their formation and development.

NMR Characterization of Ethylene/Propylene Copolymers and Propylene Impact Copolymers from MgCl2/TiCl4/ID+AlR3/ED Catalytic Systems

AbstractSummary: The aim of this work was to study the comonomer distribution and the chemical composition distribution generated by different Ziegler‐Natta (ZN) systems (different internal donors, ID, dicyclopentadienyl‐dimethoxy silane, D donor, as the external donor) and to define the potentialities of different IDs to produce improved heterophasic copolymers (HECO). A methodology to quantify the amount of ethylene‐propylene copolymer (EP) portion in ZN‐HECO and ethylene content of the EP portion by 13C‐NMR was established. By using this method, it was possible to analyze the composition of ZN‐HECO obtaining results comparable to those obtained with a more complex fractionation technique.

Supported Ziegler–Natta catalysts for propylene polymerization. Study of surface species formed at interaction of electron donors and TiCl 4 with activated MgCl 2

Adsorption of various internal electron donors (IDs) and coadsorption of these IDs with TiCl 4 on activated MgCl 2 have been studied by DRIFT and analytical techniques. As a result, the structures of the ID species on the (1 0 4) and (1 1 0) MgCl 2 surfaces were proposed. Based on the ν(C O) band resolution data for the adsorbed ID, it was estimated that the activated MgCl 2 surface contains ca. 90% of the five-coordinated Mg cations residing on the (1 0 4) surface and ca. 10% of the four-coordinated Mg cations residing on the (1 1 0) surface. The size of ID molecule was found to influence its adsorption more significantly on the (1 0 4) MgCl 2 surface than on the (1 1 0) MgCl 2 surface. Coadsorption of the various ID and TiCl 4 demonstrated that TiCl 4 formed greatly weaker surface complexes than the ID; obviously, upon coadsorption TiCl 4 occupies mainly the adsorption sites that are inaccessible for the ID because of steric reasons.

Donor Polymers Containing Benzothiadiazole and Four Thiophene Rings in Their Repeating Units with Improved Photovoltaic Performance

A series of internal donor−acceptor type of copolymers containing benzothiadiazole and four thiophene rings (bis(2,2′-dithienyl)benzothiadiazole) in their repeating units were synthesized and characterized. The effect of the position of alkyl groups attached to different thiophene rings of the new polymers on their optical, electrochemical, and photovoltaic properties was investigated and compared with poly(2,7-(9,9-dioctylfluorene)-alt-5,5-(4′,7′-di-2-thienylbenzo[c][1,2,5]thiadiazole)) (PFO-DBT). One of the new polymers, poly(2,7-(9,9-dioctylfluorene)-alt-5′,5′-(4,7-bis(3′-hexyl-2,2′-bithiophen-5-yl)benzo[c][1,2,5]thiadiazole)) (PFO-M3), showed the best device performance with a power-conversion efficiency of 2.63%, an open-circuit voltage of 0.86 V, a short-circuit current density of 5.86 mA cm−2 and a fill factor of 0.52, which is better as compared with PFO-DBT. This work demonstrated that increasing the number of thiophene rings in the repeating units of the donor−acceptor polymers is a simple and effective method to red-shift their absorption spectra and also improve their solar cell performance.

Investigation of Planar Ziegler-Natta Model Catalysts Using Attenuated Total Reflection Infrared Spectroscopy

A sensitive method is presented for the investigation of planar Ziegler-Natta model catalysts by means of attenuated total internal reflection Fourier transform infrared spectroscopy. A solution of MgCl2 in ethanol, optionally containing an internal donor, was spin-coated directly onto a planar ZnSe ATR crystal. Ethylene and propylene polymerization was monitored in situ and ex-situ, respectively, and interaction of a diester internal donor with MgCl2 and TiCl4 was investigated. The isotacticity of the polypropylene produced in the presence and absence of donor was estimated based on characteristic peaks in the infrared spectra.

Chemical structure–stereospecificity relationship of internal donor in heterogeneous Ziegler–Natta catalyst for propylene polymerization by DFT and MM calculations

The effect of chemical structure of 2,2′-disubstituted 1,3-dimethoxypropane (so-called 1,3-diether) on the performance of Ziegler–Natta (ZN) catalyst was investigated by using density functional theory and molecular mechanics. Calculation of the energy barrier during insertion of propylene reveals that the isospecific active site created on the (1 0 0) surface of MgCl 2 is more active than the aspecific active site created on the (1 1 0) surface of MgCl 2 for propylene polymerization. When the adsorption energies of various 1,3-diethers are calculated and analyzed in terms of isotacticity, it is found that the isotacticity of polypropylene increases as 1,3-diether is adsorbed more preferentially on the (1 1 0) surface. Since analysis of energetics for insertion of propylene into the active site created on the (1 1 0) surface with 1,3-diether coordinated to Mg atom in the vicinity of the active site reveals that the coordination of 1,3-diether does not transform the aspecific active site on the (1 1 0) surface into isospecific one, it is concluded that the primary function of 1,3-diether is to prevent the formation of aspecific site on the (1 1 0) surface, without significant decrease in the number of the isospecific active site created on the (1 0 0) surface. A systematic analysis of various model compounds for 1,3-diether suggests that the substitution of highly branched hydrocarbon at the C 2 position of 1,3-diether results in better performance of ZN catalyst.

Nature of Phthalates as Internal Donors in High Performance MgCl2 Supported Titanium Catalysts

High performance MgCl2 supported titanium catalyst having diisobutyl phthalate (DIBP) as internal donor has been synthesized. The organic components present in the catalyst have been studied through FTIR, 1D and 2D NMR spectroscopy. The results indicate presence of diethyl phthalate also in addition to DIBP. WAXD analysis has been done to study the features of MgCl2 crystallites. Impact of donor components on the catalyst preparation leading to reaction pathways and performance for propylene polymerization has been evaluated.