K. Rühlmann
Dresden University of Technology
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Featured researches published by K. Rühlmann.
Journal of Organometallic Chemistry | 1985
Uwe Scheim; H. Grosse-Ruyken; K. Rühlmann; A. Porzel
Abstract The acetolysis reactions of compounds of the type XSiMe 2 Cl (I) with acetic acid in the presence of acetic anhydride were studied kinetically by means of 1 H NMR spectroscopy. We found these reactions exclusively influenced by steric effects (ϱ = 0) The steric susceptibility constant (δ) of the acetolysis reaction, using alkylchlorodimethylsilanes was found to be 1.3. In this investigation the Taft E s values showed a better correlation than the E s (Si) values of Cartledge. From the rate constants of the acetolysis reactions with I (X = Cl, acetoxy or siloxy) we could then obtain for the first time E s values for Cl, acetoxy and a series of siloxy groups at silicon.
Journal of Organometallic Chemistry | 1986
Uwe Scheim; H. Grosse-Ruyken; K. Rühlmann; A. Porzel
Abstract For a series of siloxy groups at the silicon atom the inductive substituent constants σ* and σI have been determined by means of 29Si NMR spectroscopy.
Journal of Organometallic Chemistry | 1988
Uwe Scheim; A. Porzel; K. Rühlmann
Abstract The cleavage of siloxane bonds by BF 3 was investigated kinetically by 1 H NMR spectroscopy. The reactions could be evaluated by use of a pseudo-first order rate law, when a sufficiently large excess of BF 3 was used. The order with respect to BF 3 was found to be 4.7. The rate constants obtained could be correlated to σ * -values with a ϱ * -value of −1.0. The σ * -value found previously by 29 Si NMR spectroscopy for the Me 3 SiO group of 0.35 was confirmed.
Journal of Organometallic Chemistry | 1986
Uwe Scheim; K. Rühlmann; H. Grosse-Ruyken; A. Porzel
Abstract The acetolysis reaction of 1-chloro-1,3,5-trimethyl-3,5-bis(trimethylsiloxy)cyclotrisiloxane was investigated using 29 Si NMR spectroscopy. The three possible configurational isomers, formed in the synthesis, could not be separated. Taking into account the concentration of the three isomers in the mixture, the rate of their acetolysis reactions, the position and the order of the 29 Si NMR signals of the chloro- and acetoxycyclotrisiloxane isomers from one set of 29 Si NMR data information was obtained on the configuration of the isomers assigned to the NMR signals, the rate constants of the three isomers, and the stereochemistry of the acetolysis reaction. We found that the isomer present in the lowest concentration, showing the largest high field shift and the lowest reactivity has the all- cis configuration, and that the acetolysis reaction proceeds with retention of configuration.
Polymer Degradation and Stability | 1993
Holger Friedrich; Irene Jansen; K. Rühlmann
Abstract Polymeric light stabilizers were synthesized by hydrosilylation of unsaturated 2-hydroxybenzophenone derivatives or pentamethylpiperidine derivatives with different hydridosiloxanes. Investigations of the hydrosilylation reaction by NMR and HPLC show that the stabilizer groups are mainly bound to the siloxane chain by non-hydrolysable SiC bonds. When allyl ethers are used as starting material, side reactions such as ether cleavage, hydrogenation and isomerization take place. To avoid these side reactions, unsaturated ethers or esters with long methylene chains between the double bond and the oxygen were used. The polymeric light stabilizers were tested as stabilizers of polypropylene and compared with TINUVIN 770. The activity of polymeric light stabilizers decrease, with increasing molecular weight. Extraction experiments demonstrate that the polymeric stabilizers are resistant against extraction by organic solvents while TINUVIN 770 is extracted under the same conditions. Thus, our polymeric HALS show a higher effectiveness than TINUVIN 770. The polymeric HALS derivatives with the best activity have molecular weights (Mn) between 2000 and 4000.
Journal of Organometallic Chemistry | 1991
K. Käppler; A. Porzel; Uwe Scheim; K. Rühlmann
Abstract The reaction of organotrichlorosilanes with acetic acid in acetic anhydride forming organodichloroacetoxysilanes was investigated kinetically by means of 1 H-NMR spectroscopy. It was found that the reaction takes place exclusively with the acetic anhydride under the conditions used. The ϱ-value of the reaction was found to be 1.8 and the δ-value to be 1.2. A reaction mechanism is proposed.
Journal of Inorganic and Organometallic Polymers and Materials | 1991
Holger Friedrich; Irene Jansen; K. Rühlmann
Block copolymers of polystyrene and poly(dimethylsiloxane) or of polybutadiene and poly(dimethylsiloxane) with nonhydrolyzably bound 2-hydroxybenzophenone and 2,6-di-tert-butylphenol residues were prepared by terminating the “living” block copolymers with glacial acetic acid to form siloxanol end groups, followed by condensation with diethoxysilyl derivatives of the stabilizers in the presence of dibutyltin dilaurate. The polymeric UV absorbers were proved to be nonextractable from polystyrene. At Xenotest aging (40°C) the polymeric UV absorbers were less effective than 2-hydroxy-4-octyloxybenzophenone. The polymeric antioxidants were superior to antioxidants of low molecular weight both in thermooxidative aging of vulcanized polybutadiene films at 70°C and in oxygen-uptake studies with stabilized polypropylene at 180°C over long periods.
Journal of Organometallic Chemistry | 1989
Rainer Gewald; K. Rühlmann; Uwe Scheim; A. Porzel
Abstract 1-Substituted 1,3,5-trimethyl-3,5-bis(trimethylsiloxy)cyclotrisiloxanes ([(MT) 2 D X ]; X = Cl, Br, OAc, OMe, H, OH) were prepared to investigate the stereochemistry of nucleophilic substitution reactions at silicon atoms of cyclosiloxanes. The signals of the 1 H and 29 Si NMR spectra of these compounds were assigned to the three possible configurational isomers and the proportions of the isomers in the synthesized mixtures were established. The reactions of [(MT) 2 D Cl ] with alcohols and acetic acid, the bromination of [(MT) 2 D H ] and the hydrolysis of [(MT) 2 D OAc ] were studied by 1 H and 29 Si NMR spectroscopy without separating the isomer mixtures. Taking into account the intensity and the shift of the signals of the structural isomers of educts and products it was possible to determine the relative rate constants of the isomers and the stereochemistry of the reaction. It was found that all investigated reactions proceed with retention of configuration.
Phosphorus Sulfur and Silicon and The Related Elements | 1995
K. Käppler; Uwe Scheim; K. Rühlmann
Abstract The reactions of dichloromethylorganylsilanes (RSiMeCl2) and dichlorosiloxanes ([tbnd]SiOSiMeCl2) as well as of trichloroorganylsilanes (RSiCl3) and trichlorosiloxanes ([tbnd]SiOSiCl3) with lithium t-butoxide in diethyl ether were investigated kinetically by turbidimetric measurements in order to verify the inductive substituent constants σ∗ for siloxy groups determined earlier by the 29Si NMR shifts of compounds (Me3SiO)3Si—Y (Y = siloxy group) and the steric substituent constants Es for siloxy groups which were obtained by the rate constants of the acetolysis reactions of compounds ClMe2Si—Y (Y = siloxy group). The reaction constants were determined using chloroorganylsilanes to be: p∗ (RSiMeCl2) = 0.85; δ (RSiMeCl2) = 0.85; p∗ (RSiCl3) = 1.02; δ (RSiCl3) = 1.28. The correlation of lg krel – p∗ · σ∗ values of the corresponding chlorosiloxanes with Es values using σ∗- and Es-constants of siloxy groups determined earlier gave correlation straight lines with the slope of 0.81 ([tbnd]SiOSiMeCl2) or...
Journal of Organometallic Chemistry | 1988
Uwe Scheim; Robert Lehnert; A. Porzel; K. Rühlmann
Abstract 1 H NMR spectroscopy has been used in a kinetic study of the cleavage of siloxane bonds by hydrogen chloride in dioxane. The cleavages show an induction period which is associated with the autocatalytic effect of the water formed during the reaction. The kinetic behavior can be expressed in terms of a rate law that includes rate contants for cleavage by both dioxane. HCl ( k 1 ) and H 2 O·HCl( k 2 ). The k ′ 1 ( k ′ 1 k 1 · [HCl] −4 ) and k ′ 2 ( k ′ 2 k 2 · [HCl] −3 ) values correlated with σ * values; thus ϱ * values of 1.4 and 0.7 were obtained for k ′ 1 and k ′ 2 , respectively. The σ * values of 0.35 that we previously derived for the Me 3 SiO group applies in this reaction. The reaction of 1,3-bis( p -methoxyphenyl)tetramethyldisiloxane with hydrogen chloride involves cleavage of silicon-aryl rather than SiO bonds.