Search results for "POLYMERIZATION"
showing 10 items of 1689 documents
Organometallic VCl4-based catalyst supported on MgCl2(THF)2 for ethylene polymerization
1997
A Ziegler-Natta catalyst was obtained by milling VCl4 with the magnesium support in the from of the MgCl2(THF)2 complex, followed by activation with an organoaluminum compound. This catalyst was employed in low-pressure polymerization of ethylene. The system was found to offer a very high activity and to polymerize ethylene at a rate of a few hundred kg PE/(g Vh) with the resulting molecular weight of the product very high. The kinetic investgation of the polymerization process revealed over 80 % of the transition metal atoms to be involved in the forming catalytic active sites, undergoing virtually no deactivation over the period of time studied.
Weryfikacja kinetycznego modelu polimeryzacji etylenu wobec metaloorganicznych katalizatorów wanadowych na nośniku magnezowym
1998
The kinetic studies are reviewed on low-pressure polymerization of ethylene over two types of organovanadium catalysts, viz., MgCl 2(THF) 2/VCl 4/Et 2AlCl and MgCl 2(THF) 2VOCl 3Et 2AlCl, each deposited on a magnesium carrier. The polymerization rate was found to be directly related to the catalyst and monomer concentrations (Figs. 2 and 3), unless when the access of the monomer to the reactive V-C bond is restricted by diffusion. Polymer chain termination step was found to result from the reaction of the transfer onto the monomer and to be associated with the regeneration of the active site on which a new macromolecule can be formed. A kinetic model was developed for the ethylene polymeriz…
Synthesis of oxide-supported vanadium catalysts and their activity in ethylene polymerization
1999
The activity of oxide-supported vanadium-based catalyst systems (VOCl 3/Et 2AlCl) in low-pressure ethylene polymerization and the properties of the resulting polyethylenes were studied in relation to the type and mode of modification of the oxide support. Alumina, silica and an un"conventional silica-type material prepared by the sol-gel process were used as supports. Results are compared with those obtained earlier with a catalyst supported on MgCl 2(THF) 2. Of the oxides studied, the silica-type sol-gel material dehydrated and subsequently modified with Et 2AlCl proved to be the best carrier for a vanadium catalyst. The polyethylene prepared by using this catalyst support was found to exh…
Polysarcosine-Based Lipids: From Lipopolypeptoid Micelles to Stealth-Like Lipids in Langmuir Blodgett Monolayers.
2016
Amphiphiles and, in particular, PEGylated lipids or alkyl ethers represent an important class of non-ionic surfactants and have become key ingredients for long-circulating (“stealth”) liposomes. While poly-(ethylene glycol) (PEG) can be considered the gold standard for stealth-like materials, it is known to be neither a bio-based nor biodegradable material. In contrast to PEG, polysarcosine (PSar) is based on the endogenous amino acid sarcosine (N-methylated glycine), but has also demonstrated stealth-like properties in vitro, as well as in vivo. In this respect, we report on the synthesis and characterization of polysarcosine based lipids with C14 and C18 hydrocarbon chains and their end g…
Comparison of imidazolium and pyridinium ionic liquids as the media for biphasic ethylene polymerization in the presence of titanocene catalyst
2009
Chloroglinianowe ciecze jonowe z kationem 1-n-oktylo-3-metylopirydyniowym [C8-β-mpy]+[AlCl4]- lub 1-n-oktylo-4-metylopirydyniowym [C8-γ-mpy]+[AlCl4]- zastosowano jako jedną z faz w dwufazowej polimeryzacji etylenu w układzie ciecz jonowa/heksan, prowadzonej wobec katalizatora tytanocenowego (Cp2TiCl2) aktywowanego AlEtCl2. Wydajności polimeryzacji i właściwości polimerów otrzymanych z udziałem wymienionych cieczy jonowych porównano z odpowiednimi wielkościami uzyskanymi wcześniej przy udziale cieczy imidazoliowej ([C8-mim]+ [AlCl4]-) (tabele 1 i 2). Stwierdzono, że wprowadzenie do układu pirydyniowych zamiast imidazoliowych cieczy jonowych skutkuje wzrostem całkowitej wydajności procesu, wi…
Progression of Diiminopyridines: From Single Application to Catalytic Versatility
2015
Diiminopyridyl metal complexes, first characterized several decades ago, found practical application in 1998 when they were used as precatalysts in coordinative ethylene polymerization. This discovery contributed to the so-called postmetallocene revolution and triggered the large-scale experimental and theoretical research aimed at understanding diversified diiminopyridine chemistry. The results of this quest, some of which were intriguing and difficult to anticipate, are discussed and summarized in the current Review.
Self-assembly of square planar rhodium carbonyl complexes with 4,4-disubstituted-2,2′-bipyridine ligands
2020
The impact of non-covalent interactions and reaction conditions on formation and self-assembly of ionic pairs of Rh complexes with 4,4’-disubstituted bipyridine ligands ([Rh(L1)(CO)2][Rh(CO)2Cl2])n (1), [Rh(L1)2Cl2][Rh(CO)2Cl2] (2), ([Rh(L1)(CO)2][Rh(CO)2Cl2][Rh(L1)(CO)2]n([Rh(CO)2(Cl)2])n) (3), ([Rh(L2)CO2] [Rh(CO)2Cl2])n∙EtOH (4), ([Rh(L2)(CO)2])n ([Rh(CO)2Cl2])n (5) (L1 = 4,4’-dimethyl-2,2’-bipyridine, L2 = 4,4’-diamine-2,2’-bipyridine) have been studied. Packing of square planar Rh complexes favor formation of one-dimensional chains. In structure 1, the polymeric chain is formed by the alternating cationic [Rh(L1)(CO)2]+ and the anionic [Rh(CO)2Cl2]- units leading to a neutral pseudo li…
The Effect of Mechanocatalytic Pretreatment on the Structure and Depolymerization of Willow
2020
In this study, the effect of a mechanocatalytic pretreatment on the structure of willow and sugar release from pretreated willow was explored. In the mechanocatalytic approach, the pretreatment consists of solvent-free impregnation with sulfuric acid and a mechanical treatment with ball milling. Willow sawdust and pretreated samples were analyzed with field emission scanning electron microscope and X-ray diffraction. The products in the sugar solution were determined as the total reducing sugars with the 3,5-dinitrosalicylic acid method and monosaccharides with capillary electrophoresis. According to the results, milling increased the sugar production, depending on the sulfuric acid load. T…
Metal salen complexes as ethylene polymerization catalysts - effect of catalytic system composition on its activity and properties of polymerization …
2008
Zsyntetyzowano i zastosowano [po aktywacji metyloaluminoksanem (MAO) lub Et2AlCl] w charakterze katalizatorów niskociśnieniowej polimeryzacji etylenu serię salenowych kompleksów metali przejściowych różniących się rodzajem atomu centralnego (M=Ti, Zr lub V) i budową chemiczną ligandu (schemat A). Stwierdzono, że salenowe kompleksy cyrkonu są aktywne w polimeryzacji jedynie wówczas, gdy aktywator stanowi MAO, natomiast kompleksy tytanu i wanadu są aktywniejsze w przypadku gdy kokatalizatorem jest typowy związek glinoorganiczny - dietylochloroglin. Aktywność kompleksów w układzie z Et2AlCl zmienia się w szeregu V>Ti>>Zr?0, podczas gdy w odniesieniu do kompleksów aktywowanych MAO maleje ona w …
Extraordinary Performance of Carbon‐Coated Anatase TiO 2 as Sodium‐Ion Anode
2015
The synthesis of in situ polymer‐functionalized anatase TiO2 particles using an anchoring block copolymer with hydroxamate as coordinating species is reported, which yields nanoparticles (≈11 nm) in multigram scale. Thermal annealing converts the polymer brushes into a uniform and homogeneous carbon coating as proven by high resolution transmission electron microscopy and Raman spectroscopy. The strong impact of particle size as well as carbon coating on the electrochemical performance of anatase TiO2 is demonstrated. Downsizing the particles leads to higher reversible uptake/release of sodium cations per formula unit TiO2 (e.g., 0.72 eq. Na+ (11 nm) vs only 0.56 eq. Na+ (40 nm)) while the …