Search results for "Ethylene"
showing 10 items of 2589 documents
Hyaluronan-coated polybenzofulvene brushes as biomimetic materials
2016
Hyaluronic acid (HA) forms pericellular coats in many cell types that are involved in the early stages of cell adhesion by interacting with the CD44 receptor. Based on the largely recognized overexpression of the CD44 receptor in tumor tissues, a polybenzofulvene molecular brush has been enveloped into hyaluronan shells to obtain a tri-component polymer brush (TCPB) composed of intrinsically fluorescent backbones bearing nona(ethylene glycol) arms terminated with low molecular weight HA macromolecules. The nanoaggregates obtained in TCPB water dispersions were characterized on the basis of dimensions, zeta potential, and in vitro cell toxicity. This biomimetic multifunctional material beari…
Effect of hydrogen on the ethylene polymerization process over Ziegler–Natta catalysts supported on MgCl2(THF)2. II. Kinetic studies
2001
This article reports on a study of the effects of hydrogen on the activity of vanadium and titanium catalysts supported on MgCl2(THF)2 in ethylene polymerization. It was found that hydrogen did not change the stable nature of the active sites and the polydispersity index of the polyethylene obtained. The propagation rate, expressed as kp, was found to be independent of the presence and concentration of hydrogen, indicating that this reacting agent does not modify the reactivity of the active sites. However, the presence of hydrogen in the polymerization medium is responsible for partial deactivation of the active sites just before polymerization is initiated.
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…
In Vitro Evaluation of Poly(lactide-co-glycolide) In Situ Forming Gels for Bedaquiline Fumarate Salt and Pharmacokinetics Following Subcutaneous Inje…
2021
This study evaluated in vitro and in vivo drug release of bedaquiline from in situ forming gels (ISGs) containing 200 mg eq./g bedaquiline fumarate salt prepared with four different grades of poly(d,l-lactide) (PDLLA) or poly(d,l-lactide-co-glycolide) (PLGA) with a lactide/glycolide ratio of 50/50 or 75/25 and acid (A) or ester (E) end-capping in N-methyl-2-pyrrolidone at a polymer/solvent ratio of 20/80% (w/w). Mean in vitro drug release in 0.05 M phosphate buffer pH 7.4 with 1% (w/v) sodium lauryl sulphate was 37.3, 47.1, 53.3, and 62.3% within 28 days for ISGs containing PLGA5050A, PDLLA, PLGA7525A, and PLGA7525E, respectively. The data suggested that drug release was primarily controlle…
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…
The C–I･･･⁻O–N⁺ Halogen Bonds with Tetraiodoethylene and Aromatic N-oxides
2020
The nature of C–I⋯⁻O–N⁺ interactions, first of its kind, between non-fluorinated tetraiodoethylene XB-donor and pyridine N-oxides (PyNO) are studied by single-crystal X-ray diffraction (SCXRD) and Density Functional Theory (DFT) calculations. Despite the non-fluorinated nature of the C2I4, the I⋯O halogen bond distances are similar to well-known perfluorohaloalkane/-arene donor-PyNO analogues. With C2I4, oxygens of the N-oxides adopt exclusively 2-XB-coordination in contrast to the versatile bonding modes observed with perfluorinated XB-donors. The C2I4 as the XB donor forms with PyNO’s one-dimensional chain polymer structures in which the C2I4⋯(μ-PyNO)2⋯C2I4 segments manifesting two bondin…
CCDC 642893: Experimental Crystal Structure Determination
2007
Related Article: C.Peifer, D.Schollmeyer, M.Tschertsche, S.Laufer|2007|Acta Crystallogr.,Sect.E:Struct.Rep.Online|63|o1551|doi:10.1107/S1600536807009300
Reactive Compatibilization of PBT/EVA Blends with an Ethylene-Acrylic Acid Copolymer and a Low Molar Mass Bis-Oxazoline
2004
Polyesters and polyolefins form highly incompatible blends with poor properties and gross morphology that hinder any practical applications. In this work, the possibility to compatibilize an incompatible blend of poly(butylene terephthalate) (PBT) with ethylene vinyl acetate (EVA) by adding a bis-oxazoline compound, 2,2'-(1,3-phenylene)-bis(2-oxazoline) (PBO), and an ethylene acrylic acid copolymer (EAA) as compatibilizer precursors has been studied. The results indicate that the binary uncompatibilized blends show poor mechanical properties and a bad morphology with scarce adhesion between the phases. The situation is only slightly improved when the EAA is added while the best performance …