Search results for "Polymerization"
showing 10 items of 1689 documents
Kompleksy metali przejściowych z zasadami Lewisa jako prekursory katalizatorów polimeryzacji olefin. Cz. I. Postęp w komputerowym modelowaniu procesu…
2001
A review with 35 references covering molecular modeling in coordination polymerization over homogeneous and heterogeneous Ziegler-Natta catalysts. The study includes supports, cocatalysts, Lewis bases and solvents. Recent progress in elucidating the mechanisrn of elementary polymerization steps is presented against the background of rapidly deveIoping computational methods and available computational power. Theoretical studies on polymerization mcchanisms and structure of active centers are described (egns. 1-4). Authors own calculations are used to compare [MtC14(THF)2] complex-based (Mt = Ti, Hf or Zr) heterogeneous catalysts. The geometrical characteristics of precursors is presented (Ta…
Inactivation and polymerization of human neuroserpin
2010
Neuroserpin is an inhibitory enzyme, belonging to the family of serpins and involved in several pathologies, such as ischemia, Alzheimer disease, and FENIB (Familial Encephalopathy with Neuroserpin Inclusion Body). Here, we study the mechanism of neuroserpin inactivation and polymerization by different experimental techniques (static and dynamic light scattering, liquid chromatography, Fourier transform infrared spectroscopy, emission spectroscopy). Our results show that at intermediate temperatures (45-55 °C) neuroserpin forms flexible polymers with a size from a few tens to a few hundreds of nanometers. At high temperatures, above 80 °C, our results reveal a different polymeric form, reac…
Rapid one-step solvent-free acid-catalyzed mechanical depolymerization of pine sawdust to high-yield water-soluble sugars
2017
Abstract One-step absolute solvent-free acid-catalyzed mechanical depolymerization of pine sawdust (PSD) and commercially available α-cellulose to water-soluble sugars was carried out using ball milling. For comparison purposes, the commonly reported “solvent-free” mechanocatalytic depolymerization of lignocellulose method, which normally involves three steps (acid impregnation in solvent, vacuum drying, and mechanical depolymerization of lignocellulose), was performed. The 3,5-dinitrosalicylic acid (DNS) method was used to measure the total reducing sugar (TRS) of the obtained sugar solution, and major monosaccharides in the solution were analyzed by capillary electrophoresis (CE). More th…
Acidic Co-Catalysts in Cationic Gold Catalysis.
2016
A systematic study on the effects of Lewis or Bronsted acid co-catalysts in gold-catalyzed reactions was undertaken using representative reactions (O-, N-, and C-nucleophilic additions to alkynes). Through these reactions, it was demonstrated that an acidic co-catalyst can increase the catalyst turnover significantly, enabling practical reaction rates at competitive catalyst loadings (<1 mol %). Further investigation is currently underway to improve the understanding of the subtle principles underlying these experimental observations.
Impact of Organoaluminum Compounds on Phenoxyimine Ligands in Coordinative Olefin Polymerization. A Theoretical Study
2013
The reduction of the phenoxyimine moiety in three individual species—namely free ligand, aluminum complex, and titanium complex—with aluminum alkyls and aluminum hydride has been studied by means of DFT. It was demonstrated that the free phenoxyimine ligand in an equimolar mixture with trimethylaluminum does not undergo reduction. Instead, experimentally observed formation of the six-membered cyclic aluminum–phenoxyimine complex, useful in the ring-opening polymerization of lactones, takes place as the kinetically and thermodynamically favored process. However, it is anticipated that a 2-fold excess of the aluminum compound, especially aluminum hydride, acting on the resulting cyclic comple…
Vanadium-based Ziegler-Natta catalyst supported on MgCl2(THF)2 for ethylene polymerization
1996
A supported magnesium‐vanadium‐aluminium catalyst was prepared by depositing –with the use of a milling technique–VOCl3 on the MgCl2(THF)2 support and subsequent activation with diethylaluminium chloride. Catalytic activity of the obtained system for ethylene polymerization was evaluated as a function of Mg/V and Al/V ratios as well as catalyst ageing time and polymerization temperature. High concentrations of THF in the catalytic system and considerable excess of an organoaluminium co‐catalyst were found to have no deactivating action on vanadium active sites. The catalyst obtained is stable and its activity for ethylene polymerization is high. It yields polyethylene with higher molecular …
Amino-Acid-Based Polymerizable Surfactants for the Synthesis of Chiral Nanoparticles
2016
Amino-acid-based chiral surfactants with polymerizable moieties are synthesized, and a versatile approach to prepare particles thereof with a chiral surface functionality is presented. As an example of an application, the synthesized particles are tested for their ability as nucleating agents in the enantioselective crystallization of amino acid conglomerate systems, taking rac-asparagine as a model system. Particles resulting from chiral surfactants with different tail groups are compared and the results demonstrate that only the chiral nanoparticles made of the polymerizable surfactant are able to act efficiently as nucleation agent in enantioselective crystallization.
Measurements on the temperature dependence of the cationic polymerization of styrene in CH2Cl2 with CF3SO3H as catalyst
1979
The cationic polymerization of styrene in CH2Cl2 with CF3SO3H as catalyst and at low monomer concentrations shows, at −15°C, −45°C and −60°C, the same formal dependence on monomer concentration. The dependence on the catalyst concentration is approximately but not exactly of a third order.
Tailoring polymers through interplay of ligands within precatalysts: 8-(Nitro/benzhydryl-arylimino)-7,7-dimethyl-5,6-dihydroquinolylnickel halides in…
2017
A series of 8-(nitro/benzhydryl-substituted arylimino)-7,7-dimethyl-5,6-dihydroquinolines and the corresponding nickel halide complexes were synthesized and characterized. Molecular structures of representative nickel complexes were determined by single crystal X-ray diffraction, showing the dinuclear dimers with distorted square-pyramidal geometry around the nickel center. The binding energies determined by X-ray photoelectron spectroscopy (XPS) indicate the effective coordination between the sp2-nitrogen and nickel atoms as well as the influence of both the halogen ligands and the substituents within dihydroquinolines on the strength of the NiN bond. Ethylene polymerization with the nicke…
Nature of activating effect of two-step polymerization of propylene
1999
The prepolymerization effect on propylene polymerization in the presence of a TiCl 3 -based catalyst, modified by di-n-buthyl ether, was studied. The influence of prepolymerization on the electron spin resonance spectra and morphology of the catalyst, as well as the properties and the morphology of both prepolymer and regular polymerization products, was investigated. The polymer morphology was evaluated through scanning electron microscopy, polymer bulk density, and particle size distribution. Some evidence of the enhancement effect of prepolymerization on the catalyst activity and stereospecificity was obtained. No influence from prepolymerization was observed on molecular weight and its …