Top PDF Mechanistic Aspects of the Ziegler-Natta Polymerization

Mechanistic Aspects of the Ziegler-Natta Polymerization

Mechanistic Aspects of the Ziegler-Natta Polymerization

13a In the present case, the polymerization rate is faster than the alkyl exchange rate, and therefore the principal constituents of the reaction mixture are cyclopentylcapped oligomers [r]

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Investigation of Alkoxysilanes in the Presence of Hydrogen with Ziegler Natta Catalysts in Ethylene Polymerization

Investigation of Alkoxysilanes in the Presence of Hydrogen with Ziegler Natta Catalysts in Ethylene Polymerization

mentioned previously, Lewis bases were studied in many aspects in propylene polymerization. For example, the combination of internal and external donor, the mixed internal donors and/or mixed external donors [17, 18] including the different ratios of external donor to catalyst were investigated. However, the effect of external donor in ethylene polymerization is still open for discussion and less mentioned in the literature. Therefore, the aim of this work was to study the effect of alkoxysilane as external donor on catalytic activity using two commercial ZN catalysts with and without internal donor in the presence of hydrogen including thermal properties, molecular weight and its distribution of polymer in ethylene polymerization.
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Addition of a second alcohol in magnesium ethoxide synthesis as a way to vary the pore architecture of Ziegler-Natta catalysts

Addition of a second alcohol in magnesium ethoxide synthesis as a way to vary the pore architecture of Ziegler-Natta catalysts

In this study, Mg(OR) 2 samples as precursor particles for Zielger-Natta catalysts were prepared by mixing a small amount of different second alcohols in the reac- tion between metallic Mg and ethanol. The resultant influences were studied on the particle and pore char- acteristics of Ziegler-Natta catalysts. It was found that the particle morphologies were extremely sensitive to the molecular structure of the second alcohol. Sec- ond alcohols altered not only the macroparticle size and shape but also the shape of the building blocks, probably through the dissolution/precipitation equi- librium in the Mg(OR) 2 formation. The alternation of the building block shapes resulted in the generation of different pore volume distributions, which is expected to be useful for engineering the pore architecture of Ziegler-Natta catalysts. Further studies are required to clarify mechanistic aspects how a second alcohol modulates the particle formation of Mg(OR) 2 .
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A LITERATURE REVIEW ON ORAL HYPOGLYCEMIC DRUGS – MECHANISTIC ASPECTS

A LITERATURE REVIEW ON ORAL HYPOGLYCEMIC DRUGS – MECHANISTIC ASPECTS

Vol 12, Issue 11, 2019 Online 2455 3891 Print 0974 2441 A LITERATURE REVIEW ON ORAL HYPOGLYCEMIC DRUGS ? MECHANISTIC ASPECTS SYED WAJID1*, MENAKA M1, FAZIL AHMED2, SANA SAMREEN3 1Department of Pharmac[.]

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Synthetic and mechanistic studies into the kinetic resolution of alpha olefins using C1  and C2  symmetric zirconocene polymerization catalysts

Synthetic and mechanistic studies into the kinetic resolution of alpha olefins using C1 and C2 symmetric zirconocene polymerization catalysts

equiv.) and toluene (20 mL) were added to a glass reactor (125 mL, Andrews Glass Co, max. pressure 200 psig) equipped with a septum port, a three way valve connected to a quick disconnect, a large stir bar, and a pressure gauge (0-300 psig). CAUTION: this procedure should be preformed behind a blast shield. The flask was connected to the propylene tank and purged with propylene at pressures slightly greater than 1 atm for 5 minutes. The flask was pressurized to the appropriate pressure of propylene 14 for 15 minutes prior to catalyst injection. A catalyst stock solution (2 μM) was made in the glove box by dissolving the catalyst (5 mg) in toluene (3.5 mL). This solution was used within a few d and was stored at -30 ºC in the glove box. No differences in activity or tacticity were noticed for polymerizations run with older catalyst solutions. An aliquot of the stock solution (0.5 mL, 1 x 10 -3 mmol) was loaded in a 1 mL gas-tight syringe equipped with a long 18-gauge steel needle. The needle was stopped with a septum, and brought out of the glove box. The catalyst solution was injected via the septum port against the propylene pressure of the reaction. The reaction was run open to the propylene tank at the appropriate pressure with rapid stirring (700 rpm). The reaction was run for 10-30 minutes depending on the propylene pressures with lower propylene pressures requiring longer reaction times. The polymerization was stopped by slowly releasing the excess propylene pressure. The MAO was quenched by slow addition of 10% HCl/MeOH (20 mL). After stirring for 30 minutes, the polymer was further purified by precipitation into methanol (400 mL). This mixture was allowed to stir a few hours to dissolve all of the aluminoxane. The polymer was isolated by filtration and washed with fresh methanol (3 x 10 mL). The polymer was dried in vacuo at 110 ºC overnight. The polymer microstructure was determined by 13 C{ 1 H} NMR (1,1,2,2-tetrachloroethane-d 2 ,
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Micheal Ziegler Athiang Makuoi

Micheal Ziegler Athiang Makuoi

Women and girls are the most vulnerable during conflict 6 and it is the duty of international community to come together and find out why this is, and how we can mitigate this problem[r]

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Mechanistic aspects of NF-κB regulation_The emerging role of phosphorylation and proteolysis.pdf

Mechanistic aspects of NF-κB regulation_The emerging role of phosphorylation and proteolysis.pdf

A Unifying Mechanism of NF-KB Activation: Phosphorylation of IKB Signals Ubiquitination and Subsequent Degradation by the Proteasome Since the inducible phosphorylati[r]

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Mechanistic aspects of biosynthesis of silver nanoparticles by several Fusarium oxysporum strains

Mechanistic aspects of biosynthesis of silver nanoparticles by several Fusarium oxysporum strains

ND conceived the study, together with OLA and EE and participated in its design and coordination and collected all the data and wrote the paper. PDM obtained all the SEM views, performed the enzymatic assays, the electron shuttling aspects and discussed the three related parts in the manuscript. GIHS performed all the fungal tests and measured all the spectroscopic variations of the plasmon resonance of the silver nanoparticles supervised by EE. OLA also supervised all the nanoparticles aspects in this work. All authors read and approved the final manuscript. Acknowledgements

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The mechanistic and evolutionary aspects of the 2′- and 3′-OH paradigm in biosynthetic machinery

The mechanistic and evolutionary aspects of the 2′- and 3′-OH paradigm in biosynthetic machinery

and 3′ hydroxyls of the conserved tRNA 3′-terminal adenosine (A76) observed during peptide bond forma- tion at the peptidyl transferase centre (PTC) of the ribo- some co-evolved with the two modes of attack on the aminoacyl-adenylate carbonyl typical of the two classes of aaRSs and also with the isomerase activity of EF-Tu. The authors recognize the fundamental roles of the 3′- OH and 2′-OH groups in protein synthesis and develop their arguments with several examples that highlight the relevance of the 2′-OH and 3′-OH chemistry at the amino acid activation, editing, transfer to the elongation factor and PTC levels. This is an expected outcome of the 2′-OH and 3′-OH multilayered chemistry, it would be surprising if it worked in a different manner. The value of this highly descriptive hypothesis paper that re- views old concepts is that it highlights the overlooked chemistry of the 2′-OH and 3′-OH, bringing it to current debate. This is important and sufficient to rec- ommend its publication. However, there are several aspects of the paper that should be improved before publication, namely:
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Structural and mechanistic aspects influencing the ADAM10-mediated shedding of the prion protein

Structural and mechanistic aspects influencing the ADAM10-mediated shedding of the prion protein

Proteolytic shedding of the prion protein has most re- cently attracted scientific interest with regard to di- verse pathological conditions affecting the brain. Using a novel antibody for the specific detection of shed PrP, we demonstrated structural and regulatory aspects influencing this cleavage and show that it can - in principle - be pharmacologically manipulated. The latter, together with the rather ubiquitous expres- sion of PrP C in several tissues and cell lines, as well as the lack of compensation by other proteases discussed above, also turns (i) PrP C into an ideal “ control ” substrate, (ii) assessment of PrP C shedding into a reliable “ read out ” , and (iii) our antibody into a valuable tool for any future studies investigating ADAM10-mediated cleavages and their pharmaco- logical accessibility. With direct regard to the shed- ding of PrP C , both, therapeutic stimulation as well as inhibition, may be conceivable depending on the pathological context.
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Reactions of cationic (allyl)Ni(II) complexes with 1,3-dienes and olefins : polymerization and mechanistic studies

Reactions of cationic (allyl)Ni(II) complexes with 1,3-dienes and olefins : polymerization and mechanistic studies

The stereoselective polymerization of 1,3-dienes has been a significant challenge and efforts have been made in both academia and industry to design metal catalysts that polymerize 1,3-dienes in a selective fashion. 1 The unique microstructures (cis-1,4, trans- 1,4, 1,2, 3,4) that exist for diene polymers influence polymer properties and therefore applications and potential uses of these materials (see chapter 1). For example, cis-1,4- polybutadiene is important because of its industrial use for synthetic rubber production. 2 The integrity of synthetic rubber is highly dependent on the percent 1,4-cis content. There is a significant difference in the elastic properties between 98% and 99% cis-1,4- polybutadiene. 3 Complexes containing early metals, lanthanides (Ln), and late metals have been synthesized and used as stereoselective 1,3-diene polymerization catalysts.
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Investigation of Effective Factors on the 4th Generation Ziegler-Natta Catalyst Activity by Design of Experiments - Volume 2 Number 4 (Aug. 2011) - IJCEA

Investigation of Effective Factors on the 4th Generation Ziegler-Natta Catalyst Activity by Design of Experiments - Volume 2 Number 4 (Aug. 2011) - IJCEA

In studies on the complexation of different alkoxysilanes with triethylaluminium Iiskola et al. [12] found that, at room temperature, TEA and alkoxysilane instantly form a 1:1 complex independent of the number of alkoxy groups in the silane. The stability of the complex depends on the structure of the alkoxysilane, Al/Si mole ratio, temperature and time. Under typical polymerization conditions, the greatest part of the complex seems to persist in its original form. Spitz et al. [3] studied the effect of triethylaluminium and triethoxyphenylsilane concentration and Al/Si mole ratio on MgCl 2 /dibutylphthalate/TiCl 4 . It was found that at increasing
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Mechanistic aspects of the monooxygenase system from Methylococcus capsulatus

Mechanistic aspects of the monooxygenase system from Methylococcus capsulatus

A Thesis Submitted for the Degree of PhD at the University of Warwick Permanent WRAP URL: http://wrap.warwick.ac.uk/110294 Copyright and reuse: This thesis is made available online and i[r]

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Preparation of Ultra High Molecular Weight Polyethylene Using Ziegler-Natta Catalyst System: Optimization of Parameters by Response Surface Methodology

Preparation of Ultra High Molecular Weight Polyethylene Using Ziegler-Natta Catalyst System: Optimization of Parameters by Response Surface Methodology

Ethylene monomer (industrial-grade) was supplied by Amir Kabir Petrochemical Co. (Mahshahr, Iran) and further purified by passing through molecular sieve columns (4A type having a 4-A pore size). High- purity argon (≥99.999%) was used to produce an inert atmosphere for the catalytic system preparation as well as the polymerization. Industrial grade n-hexane was supported by Amir Kabir Petrochemical

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Synthetic, reactivity, and mechanistic studies relevant to olefin oligomerization and polymerization

Synthetic, reactivity, and mechanistic studies relevant to olefin oligomerization and polymerization

bridged bisphenolate was found to undergo intramolecular CH activation faster than metal-alkyl protonolysis by a pendant phenol, un unprecedented process for early metals. An α-H abstraction reaction has afforded access to a tantalum benzylidene supported by the pyridine linked bisphenolate. Isotope labeling studies and variable temperature kinetics measurements were used to investigate the mechanisms of these transformations. Group 4 complexes supported by the present bisphenolates were found to have interesting catalytic behavior for the propylene polymerization and oligomerization, upon activation with excess MAO. The propylene polymerization activity of present zirconium complexes is excellent, exceeding 10 6 g polypropylene / (mol Zr • h), in some cases.
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D1T3 - Paul Sebastian Ziegler - Hacking in the Far East.pdf

D1T3 - Paul Sebastian Ziegler - Hacking in the Far East.pdf

Aufbau eines XSS-Angriffs gegen eine ungesicherte Webanwendung | 2 Effekte, die ein Angreifer durch XSS hervorrufen kann | 8 Schutzmechanismen, die zu kurz greifen | 19 Der[r]

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Modeling and Simulation of the Autocatalytic Kinetics of Haemoglobin SS Polymerization: Onset of Polymerization

Modeling and Simulation of the Autocatalytic Kinetics of Haemoglobin SS Polymerization: Onset of Polymerization

Therapeutic options available from kinetic studies and currently in use in some cases, are: In particular, the discovery of the enormous concentration dependence of the rate of polymerization suggested decreasing the in- tracellular haemoglobin concentration as a new approach to the treatment of sickle cell disease; Decreasing the intracellular haemoglobin concentration (by crowding) with non-polymerizing agents like fetal haemoglobin Hb F or normal Hb AA (as currently used in Stroke Prevention Trial in Sickle Cell Anemia, STOP). A decrease in the intracellular haemoglobin concentration of only 10% - 15% has been predicted to have some therapeutic ef- fect as evidenced in blood exchange therapies; Increasing the oxygen affinity so that the concentration of mole- cules capable of polymerization will be grossly decreased; Drugs that will prevent cellular dehydration.
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Atom Transfer Radical Polymerization (ATRP)in Amplification-by-Polymerization for DNA Sensing

Atom Transfer Radical Polymerization (ATRP)in Amplification-by-Polymerization for DNA Sensing

As for metal catalysts, a complex of a copper (I) halide and 2,2’-bipyridyl is the most widely used catalyst. 104, 105 The catalyst undergoes a one-electron oxidation with concomitant abstraction of a halogen atom from a substrate. Ni, 106 Pd, 107 Ru, 108 Fe, 109 and other metals 110 have been used as well. So far, the copper-based ATRP system has been adapted successfully for the controlled/living polymerization of styrenes, acrylates, methacrylates, acrylonitrile, and other monomers. The current generation of catalyst systems is not sufficiently efficient to polymerize less reactive monomers, such as ethylene, a-olefins, vinyl chloride, and vinyl acetate, which produce non-stabilized, highly reactive radicals. Acrylic and methacrylic acid cannot be polymerized with currently available ATRP catalysts, because these monomers react rapidly with the metal complexes to form metal carboxylates which are inefficient deactivators and cannot be reduced to active ATRP catalysts.
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Homo polymerization and co-polymerization of n-pentenyl carbazole (N-PCz) by cold plasma and radicalic polymerization (glow discharges)

Homo polymerization and co-polymerization of n-pentenyl carbazole (N-PCz) by cold plasma and radicalic polymerization (glow discharges)

Key words: Electrophotographie, charge transfer, donor of electrons: acceptor of electrons, donor-acceptor complexes, cold plasma, thin film deposition.. phenomenon of the photoconductio[r]

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Polymerization of propylene in a minireactor: Effect of polymerization conditions on particle morphology

Polymerization of propylene in a minireactor: Effect of polymerization conditions on particle morphology

This series of experiments (NC6-1,2, NC4-1) was in- tended to explore the effect of the reaction progress on the particle morphology, so a number of experiments performed at similar conditions and stopped at differ- ent times. Figure 13 shows the morphology of parti- cles obtained from the polymerizations at 70°C and 8 bar, in different polymerization times. It is obvious in Figure 13 that particle morphology is transformed from a smooth closed surface to a rough porous as the reaction proceeds. Figure 13 clearly shows the devel- opment of the particle morphology. In Figure 13a, the particle morphology after 3 min is shown. The cauli- flower like morphology of the particle shows disinte- gration of clusters and onset of crack formation after 3 min. Figure 13b shows the growth of initial cracks and initiation of new cracks. In Figure 13c, the devel- opment of subglobules and appearance of wide cracks and holes are obvious. Therefore, three different steps in the development of particle morphology can be dis- tinguished. The first step is initiation of cracks in the particle due to internal particle pressure as reaction proceeds and more polymers are produced inside the particle. In the second step, fragments can be clearly distinguished and cracks get wider as a result of particle growth. In this step, cracks initiate at each fragment.
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