Search results for "Polymerization"
showing 10 items of 1689 documents
Synthesis and X-ray structure of cationic β-diimine palladium complexes containing π-methallyl ligand
2005
High yield of cationic palladium β-diimine complexes [(CH 2 (MeCNAr) 2 )Pd(η 3 -C 4 H 7 )][Y] (Ar = C 6 H 5 , Y = PF 6 (8); 2-Me-C 6 H 4 , Y = PF 6 (9); 2,6-Me 2 -C 6 H 3 , Y = PF 6 (10); 2,6-iPr 2 -C 6 H 3 , Y = PF 6 (11), Y = B(3,5-(CF 3 ) 2 -C 6 H 3 ) 4 (12)) have been obtained by an oxidative addition of the methallyloxyphosphonium salts (5, 6) to a preformed complex Pd(dba) 2 (7) in the presence of the β-iminoamine ligands (1-4). These complexes are thermally stable and have been characterized by 'H and 1 3 C{ 1 H} NMR as well as IR spectroscopy. The structure of the cationic allyl palladium complex (12) has been solved by X-ray crystallography.
The first member of a second generation family of ligands derived from metal-ion assisted reactivity of di-2,6-(2-pyridylcarbonyl)pyridine: Synthesis…
2012
Abstract Nucleophilic attack by the carbanion −CH2COCH3 at the carbonyl carbon atoms of 2,6-di-(2-pyridylcarbonyl)pyridine, pyCOpyCOpy, in the presence of Mnn+ ions under basic conditions has yielded the cationic cluster [Mn4(OH)2(L)2(H2O)2](ClO4)4 (1), where L2− is the (py)C(CH2COCH3)(O−)(py)C(CH2COCH3)(O−)(py) dianion. The cluster cation possesses a planar {MnII2MnIII2(μ3-OH)2(μ-OR)4}4+ rhombus core, resulting from two μ3-OH− ions and two η1:η2:η1:η1:η1:η2:η1:μ3 bridging L2− groups from the in situ formed ligand. Complex 1 is antiferromagnetically coupled with an unusual S = 2 ground state resulting from spin frustration effects within the triangular Mn3 subunits of the cluster.
Polymerization in black lipid membranes. Influence on ion transport
1986
A variety of different lipids containing dienoyl groups in the side chains were tested for membrane formation using the planar lipid bilayer approach. One of these lipids formed stable bilayers which could be polymerized using UV-illumination. The influence of the polymerization was studied in monolayers, lipid vesicles and planar bilayers. The stability of the lipid bilayer membranes was increased by polymerization. Thus, the lifetime of the membranes increased from about 1 h to 4–5 h or longer. Furthermore, the specific conductance of unmodified membranes and of carrier-mediated transport is reduced. The transport of lipophilic ions was investigated as a function of polymerization using t…
Average versus local structure in K2NiF4-type LaSrAlO4: direct experimental evidence of local cationic ordering
2012
The long-range ordering of a crystalline material can be accurately determined by analyzing the Bragg intensities and positions. In contrast, direct observation of short-range ordering in crystalline materials, which is increasingly considered of fundamental importance to unravel the structure-property relationships that underpin their technological applications, is a challenging task. In this study we have investigated the structure of LaSrAlO4, a representative example of compounds with the K2NiF4-type structure. By the combined use of synchrotron and neutron diffraction, pair distribution function analysis, Al-27 MQMAS NMR and atomistic simulations we have highlighted differences between…
Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers
2021
Bis[1]benzothieno[1,4]thiazines (BBTT) are particularly electron-rich S,N-heteropentacenes and their radical cations and dications can be relevant intermediates in charge transport materials. All three regioisomers of N-p-fluorophenyl-BBTT (syn–syn, syn–anti, and anti–anti) were studied. A reliable preparation of radical cations and dications using antimony pentachloride as an oxidant gives deeply colored salts. The electronic structure of the radical cations was assessed by EPR spectroscopy, whereas dicationic structures were characterized by NMR spectroscopy. In addition, a deeper insight into the electronic structure was experimentally and computationally obtained by UV/Vis spectroscopy …
Syntheses, Structure, and Reactivity of Chiral Titanium Compounds: Procatalysts for Olefin Polymerization
2001
Titanium complexes with chelating alkoxo ligands have been synthesised with the aim to investigate titanium active centres in catalytic ethylene polymerisation. The titanium complexes cis-[TiCl2(η2-maltolato)2] (1, 89 %), and cis-[TiCl2(η2-guaiacolato)2] (2, 80 %) were prepared by direct reaction of TiCl4 with maltol and guaiacol in toluene. The addition of maltol to [Ti(OiPr)4] in THF results in the formation of species [Ti(OiPr)2(maltolato)2] (3, 82 %). The titanium compound cis-[Ti(OEt)2(η2-maltolato)2] (4, 74 %) was obtained by the transesterification reaction of species 3 with CH3CO2Et. When compound 4 is dissolved in THF a dinuclear species [Ti2(μ-OEt)2(OEt)4(η2-maltolato)2] (5, 45 %)…
Synthesis and structure of stable cis-dimethyl complex of oxotungsten(VI)
2007
Abstract Oxotungsten(VI) complex cis -[WO(L t Bu )Me 2 ] (L t Bu = methylamino- N , N -bis(2-methylene-4-methyl-6- tert -butylphenolate) dianion) was prepared by the transmetallation reaction of [WO(L t Bu )Cl 2 ] (either cis or trans isomer) with methyl magnesium iodide. This unexpectedly stable dialkyl complex can be activated by Et 2 AlCl to catalyze the ring-opening metathesis polymerization of norbornene.
Stamping of monomeric SAMs as a route to structured crystallization templates: patterned titania films.
2000
Gold-coated glass slides have be patterned by using self-assembled monolayers (SAM) of alkane thiols. Through the use of a special thiol terminated with a styrene monomer, microstructures of 5 to 10 microm width and 70 A height have been formed on the surface by graft polymerization of styrene. These patterned gold slides have then been used to template the precipitation of thin titania films from ethanolic solutions of titanium isopropoxide to create microstructured architectures in the film. Plasmon resonance spectra have established the presence of different steps in the process and have been used to follow the kinetics of the precipitation of titania on the surface. The structured TiO2 …
Poly(glycolide) multi-arm star polymers: Improved solubility via limited arm length.
2010
Due to the low solubility of poly(glycolic acid) (PGA), its use is generally limited to the synthesis of random copolyesters with other hydroxy acids, such as lactic acid, or to applications that permit direct processing from the polymer melt. Insolubility is generally observed for PGA when the degree of polymerization exceeds 20. Here we present a strategy that allows the preparation of PGA-based multi-arm structures which significantly exceed the molecular weight of processable oligomeric linear PGA (<1000 g/mol). This was achieved by the use of a multifunctional hyperbranched polyglycerol (PG) macroinitiator and the tin(II)-2-ethylhexanoate catalyzed ring-opening polymerization of gly…
Üuber eine abgekürzte Fraktioniermethode zur Bestimmung von Molekulargewichtsverteilungen
1950
Es wird ein Verfahren beschrieben, welches die Breite und ungefahre Gestalt der Verteilungskurve cines polymolekularen Stoffs auf Grund folgender experimenteller Daten zu bestimmen erlaubt: 1 Mittlerer Polymerisationsgrad (z. B. durch eine osmotische Bestimmung). 2 Gewichtsanteil und mittlerer Polymerisationsgrad einer obersten Fraktion. 3 Gewichtsanteil und mittlerer Polymerisationsgrad einer untersten Fraktion. Anwendungsbereich und Grenzen des neuen Verfahrens werden experimentell ermittelt. A method is described permitting to determine latitude and approximate shape of the distribution curve of a polymolecular substance by means of the following experimental data: 1 Average degree of po…