Search results for "olefin"

Studien zum Vorgang der Wasserstoffübertragung, 39. Langlebige Hydrierkatalysatoren durch kovalente Verknüpfung von Phosphin-Rhodium-Komplexen an Aer…

1976

Homogene Phosphin-Rhodium-Katalysatoren werden durch kovalente Bindung an ‘Aminoaerosil’ heterogenisiert. Die Abhangigkeit der Hydriergeschwindigkeit von der Entfernung der aktiven Zentren zur Oberflache, von der Temperatur, vom Losungsmittel und von der Struktur der eingesetzten Olefine wird untersucht. Studies on the Occurrence of Hydrogen Transfer, 39. — Long-Lived Hydrogenation Catalyst by Covalent Fixation of Phosphine-Rhodium-Complexes on the Surface of Aerosil 200 The covalent binding of hitherto homogeneous phosphine-rhodium catalysts to “Amino-aerosil” is described. The dependence of the rate of catalysed hydrogenation upon the distance between the reaction centre and the silica su…

The effect of reaction conditions on the chain end structure and functionality during dehydrochlorination oftert-chlorine-telechelic polyisobutylene …

1998

Dehydrochlorination of tert-chlorine-telechelic polyisobutylene with potassium tert-butoxide in refluxing tetrahydrofuran is quantitative after 22 h, but results in ca. 3% endo olefin chain ends which are not reactive in some subsequent functionalization reactions. The formation of these undesired structures is most likely due to simultaneous thermally induced HCl loss. Lower temperatures and longer reaction times led to exclusive formation of external double bonds in some cases but to incomplete dehydrochlorination.

Oxovanadium(IV) complexes with [ONNO]-chelating ligands as catalysts for ethylene homo- and copolymerization

2014

Oxovanadium(IV) complexes with (ONNO)-type tetradentate Schiff base ligands: salen, acacen, aceten, acetph (H2salen = N,N'-ethylenebis(salicylideneimine), H2aceten = N,N'-ethylenebis(2-hydroxyacetophenoneimine), H2acacen = N,N'-ethylenebis(acetylacetonimine), H 2 acetph = N ,N ' -phenylene-1,2-b is (2-hydroxyacetophenoneimine)), were the first time investi- gated in ethylene polymerization and ethylene/1-octene copo- lymerization processes. In general, all these complexes are moderately active precatalyst for ethylene polymerization up- on activation with EtAlCl2 and they give high molecular weight linear polyethylenes. Their activity in copolymeriza- tion was found relatively low. However,…

Uncatalyzed photofunctionalization of C-H bonds

2010

Influence of the matrix on photo-oxidative degradation of polyolefin based nanocomposite films

2008

Effect of Different Matrices and Nanofillers on the Rheological Behavior of Polymer-Clay Nanocomposites

2010

In this work, a comprehensive study of the rheologi-cal behavior under shear and isothermal and nonisothermal elongational flow of low density polyethylene (LDPE) and ethylene-vinyl acetate copolymer (EVA) based nanocomposites was reported to evaluate their "filmability", that is, the ability of these material to be processed for film forming applications. The influence of two different kinds of organoclay - namely Cloisite 15A and Cloisite 30B - and their concentration was evaluated. The presence of filler clearly affects the rheological behavior in oscil-latory state of polyolefin-based nanocomposites but the increase of complex viscosity and the shear thinning are not dramatic. A larger …

Novel silicon microparticles to improve sunlight stability of raw polypropylene

2015

Oxidation of polyolefins by ultraviolet/visible irradiation is a significant limitation for their use in several technological applications. The use of high-tech additives such as silicon microparticles becomes a compositing strategy that can improve the performance of these materials at long-term service conditions. Silicon particles were added to non-additivated raw polypropylene (PP) prepared by hot melt extrusion and subjected to accelerated sunlight irradiation tests. The stability of thermal properties, mechanical performance and thermal decomposition behaviour of composites was evaluated by differential scanning calorimetry, dynamic mechanical thermal analysis and thermogravimetry. T…

Stepwise synthesis and selective dimerisation of bis- and trisloop tetra-urea calix[4]arenes.

2008

Tetra-urea calix[4]arenes substituted with four mono- or bisalkenyl residues have been converted into bis- or tetraloop compounds by intramolecular olefin metathesis, with use of a tetratosylurea calix[4]arene as template. The same strategy has now been used to synthesise trisloop compounds and bisloop compounds with adjacent loops, completing the series of the loop-containing tetra-urea derivatives. A tetra-urea calix[4]arene of the AABB type, where A stands for a bisalkenyl- and B for a monoalkenyl-substituted urea unit, was used as precursor for the three loops. It was easily synthesised from a tetraamino calix[4]arene in which two adjacent amino groups were Boc-protected. The ABCB-type …

Photochemical Generation of Cyclophanes from 1,3,5-Trisubstituted Benzenes with Chalcone Chromophores

2007

(E,E,E)-1,3,5-Tricinnamoylbenzene (7a) photodimerizes in solution to the [4.4.4](1,3,5)cyclophane 8a. The process consists of three consecutive steps in which cisoid enone conformations of 7a react in regio- and stereoselective anti-head-to-head cycloadditions. (E,E,E)-1,3,5-Tris(3-oxo-3-phenylpropenyl)benzene (13a), an isomer of 7 with reversed enone units, shows a single [2π+2π] cycloaddition of the same type. Due to steric reasons, it is afterwards not capable of intramolecular processes and oligomerizes by intermolecular photocycloadditions. Photolyses in the crystalline state yield dimers by topochemically controlled syn-head-to-tail processes (7a → 10a, 13a → 15a). An efficient dimeri…

Early lanthanide organometallic hydrides: electronic and steric control of the stability

2000

Abstract Steric and electronic effects on the stability of early lanthanide, neodymium and samarium, organometallic hydrides are discussed. The instability of (tmp)2SmH (tmp=tetramethylphospholyl) is attributed to electronic factors and the low stability of (tBuC5H4)2SmH is related to steric reasons. The analogous neodymium hydride (tBuC5H4)2NdH, could not be obtained, whereas the more hindered triethylborohydride was formed. Access to bisphospholyl bridged heterobimetallic ruthenium–lanthanide hydrides is also related to the size of the lanthanide atom. The bimetallic structures are accessible for lanthanides of ionic radii smaller than 1 A. The role of organometallic hydrides versus alkyl…