Search results for "Catalysis"

Poly(carbonate) copolymers with a tailored number of hydroxyl groups from glycidyl ethers and CO2

2014

Functional poly(carbonate)s with multiple hydroxyl functionalities have been prepared by copolymerization of carbon dioxide (CO2) with glycidyl methyl ether (GME) and benzyl glycidyl ether (BGE) in various ratios, using a diethylzinc–pyrogallol catalyst system. Subsequent catalytic hydrogenation was employed for removal of the benzyl protecting groups at the polymer backbone. A series of copolymers with varying comonomer fractions from 0 to 100% was obtained. The copolymers possessed a broad range of molecular weights from 9000 to 30 000 g mol−1 and showed polydispersities Mw/Mn between 2.4 and 3.6. The materials were characterized via1H and 13C NMR, SEC and differential scanning calorimetr…

Crystalline CO2 -Based Aliphatic Polycarbonates with Long Alkyl Chains

2018

Carbon dioxide (CO2 ) is an easily available, renewable carbon source and can be utilized as a comonomer in the catalytic ring-opening polymerization of epoxides to generate aliphatic polycarbonates. Dodecyl glycidyl ether (DDGE) is copolymerized with CO2 and propylene oxide (PO) to obtain aliphatic poly(dodecyl glycidyl ether carbonate) and poly(propylene carbonate-co-dodecyl glycidyl ether carbonate) copolymers, respectively. The polymerization proceeds at 30 °C and high CO2 pressure utilizing the established binary catalytic system (R,R)-Co(salen)Cl/[PPN]Cl. The copolymers with varying DDGE:PO ratios are characterized via NMR, FT-IR spectroscopy, and SEC, exhibiting high molecular weight…

Synthesis of aldonamide siloxanes by hydrosilylation

1998

Abstract The synthesis of hydrophobic/hydrophilic hybrid polymers based on polydimethylsiloxanes (PDMS) and carbohydrate derivatives involving a hydrosilylation step is reported. Starting with poly(dimethyl- co -hydromethyl)siloxanes (PDMS- co -HMS), O -acetylated N -allylaldonamides of various sugars can be attached to the siloxane backbone using platinum catalysts. The characteristics of different transition metal complexes in the polymer-analogous formation of SiC bonds are investigated. A generalized reaction pathway applicable to several reducing carbohydrates is established to synthesize aldonamide siloxanes in a broad variety of molecular weight and composition. The products obtaine…

Biphasic ethylene polymerisation using 1-n-alkyl-3-methylimidazolium tetrachloroaluminate ionic liquid as a medium of the Cp2TiCl2 titanocene catalyst

2008

Abstract A systematic analysis was performed on a series of 1- n -alkyl-3-methylimidazolium tetrachloroaluminates (where alkyl = ethyl, butyl, hexyl, and octyl), applied as a medium of the Cp 2 TiCl 2 titanocene catalyst, to evaluate the influence of the physical properties of the ionic liquids on the polymerisation reaction carried out in the biphasic ionic liquid/hexane mode. Two alkylaluminium compounds, AlEtCl 2 and AlEt 2 Cl, were used as activators. The influence of the activator/catalyst molar ratio on the performance of the ethylene polymerisation was determined for each ionic liquid studied. The best results were obtained using 1- n -octyl-3-methylimidazolium tetrachloroaluminate. …

Polymerizations of Cyclic Esters Catalyzed by Titanium Complexes Having Chalcogen-Bridged Chelating Diaryloxo Ligands

2002

A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands, [TiX2{2,2‘-Te(4-Me-6-tBu-C6H2O)2}]2 (5:  X = Cl; 6:  X = OiPr), catalyzed the ring-opening polymerization of cyclic esters such as e-caprolactone, δ-valerolactone, and l-lactide. The strong dependence of polymerizations on the solvent was observed in this catalytic system. When the polymerizations of e-caprolactone and l-lactide were carried out in toluene at 100 °C, tellurium-bridged bis(aryloxo)titanium complex 5 was found to give polymers with rather broad molecular weight distribution due to back-biting. When the polymerizations of e-caprolactone and l-lactide was carried out in anisole or in dioxane…

Polymerizable phospholipid analogues--new stable biomembrane and cell models.

1980

On the handedness of helical aggregates of C3 tricarboxamides: a multichiroptical characterization

2015

A complete chiroptical characterization of the supramolecular polymers formed by tricarboxamides (S)-1 and (R)-1 is performed using ECD, VCD and CPL dichroic techniques. The helical aggregates show an intense CPL signal and their absolute P- or M-configuration is assigned with the help of theoretical calculations.

The effect of potassium on the selective oxidation ofn-butane and ethane over Al2O3-supported vanadia catalysts

1995

The catalytic properties of undoped and K-doped (K/V atomic ratio of 0.5) Al2O3-supported vanadia catalysts (∼4.5 wt% of V2O5) for the oxidation ofn-butane and ethane were studied. Isolated tetrahedral V5+ species are mainly observed in both undoped and K-doped samples. The incorporation of potassium decreases both the reducibility of surface vanadium species and the number of surface acid sites. Potassium-free vanadium catalysts show a high selectivity during the oxidative dehydrogenation (ODH) of ethane but a low selectivity during the ODH ofn-butane. However, the presence of potassium on the vanadium catalysts strongly influences their catalytic properties, increasing the selectivity to …

Crown ethers derived from bicyclocalix[4]arenes as chromoionophores

2001

The synthesis of calix[4]arenes in which opposite phenolic units are connected by a poly(oxyethylene) bridge at the narrow rim and a 2,6-dimethylene-4-nitrophenol bridge at the wide rim is reported. For two derivatives with tetra- (4) and penta(oxyethylene) (5) bridges UV-Vis spectrophotometric studies were carried out in buffered solution in the presence of alkali metal ions. Their complexation was associated with changes in their UV-Vis spectra, especially with an increase of the absorption band at 450 nm. For 4 and 5 this was most intense in the presence of potassium and caesium ions, respectively, indicating that the calixarene with the shorter crown ether bridge is selective towards po…

Die alkoholyse des triethylsilans katalysiert von [(CH3)3P]2Ru(CO)2Cl2

1983

Abstract [(CH 3 ) 3 Pl 2 Ru(CO) 2 Cl 2 is an effective catalyst for the reaction of alcohols with triethylsilane. The rate of this reaction varies with the substituents in the hydroxy compound; it is fastest for short primary alcohols. Even in the presence of groups which can be hydrosilated (CC triple or double bonds, as well as ketones), a hydroxy group reacts preferably and completely with the silane. Kinetic experiments have been performed with the system Et 3 SiH/CH 3 CH(OH)COOEt/Ru complex.