Search results for "polymerization"

Adsorption of water in Na-LTA zeolites: an ab initio molecular dynamics investigation

2021

The very wide range of applications of LTA zeolites, including the storage of tritiated water, implies that a detailed and accurate atomic-scale description of the adsorption processes taking place in their structure is crucial. To unravel with an unprecedented accuracy the mechanisms behind the water filling in NaA, we have conducted a systematic ab initio molecular dynamics investigation. Two LTA structural models, the conventional Z4A and the reduced one ZK4, have been used for static and dynamic ab initio calculations, respectively. After assessing this reduced model with comparative static DFT calculations, we start the filling of the α and β cages by water, molecule by molecule. This …

Kinetische Untersuchungen über die kationische Polymerisation von wasserfreiem Formaldehyd. 40. Mitt. Über polyoxymethylene

1971

Die Polymerisation von Formaldehyd in atherischer Losung bei −78°C mit SnCl4 und HClO4 als Initiatoren wurde untersucht. Die Konzentration der aktiven Zentren (Polyoxymethylen-Kationen) wurde bestimmt, indem die Polymerisationen durch Zugabe eines grosen Uberschusses an n-Amylalkohol abgebrochen und die entstandenen Pentoxylendgruppen nach Reinigung und Hydrolyse der Polymeren gaschromatographisch bestimmt wurden. Die Initiierung der Polymerisationerfolgt rasch und fuhrt zu vollstandigem Umsatz des Initiators wahrend der ersten Minuten. Unter gunstigen Reaktionsbedingungen ergibt jedes eingesetzte Initiatormolekul ein Polyoxymethylene-Kation. Ein kinetischer Abbruch wurde nicht festgestellt…

Änderung der polymerisationsaktivität und der zahl aktiver zentren bei der alterung der katalysatorsysteme Al(C2H5)3/TiCl3 und Al(C2H5)2Cl/TiCl3. Zur…

1965

Es wird das Alterungsverhalten der Katalysatorsysteme Al(C2H5)3/TiCl3 und Al(C2H5)2Cl/TiCl3 untersucht; an den drei Monomeren Athylen, Propylen und Buten-1 wird die Anderung der Polymerisationsaktivitat in Abhangigkeit vom Al/Ti-Verhaltnis fur verschiedene Alterungszeiten des Gesamtkatalysators gemessen. Nach anfanglichem Anstieg zeigt sich ein mehr oder weniger starker Abfall der Polymerisationsaktivitat mit steigender Alterungszeit und wachsendem Al/Ti-Verhaltnis. Die Aktivitatsanderung ist unter vergleichbaren Bedingungen fur die drei Monomeren verschieden. Daraus wird auf das Vorhandensein verschieden aktiver Zentren fur die Polymerisation der Monomeren geschlossen. The aging of the cat…

Eine methode zur untersuchung der polymerisation von äthylen und gasförmigen α-olefinen bei normaldruck. Zur polymerisation mit metallorganischen mis…

1963

Es wird eine einfache Apparatur zur Messung des Reaktionsverlaufs bei der Polymerisation gasformiger Monomerer beschrieben. In einem geschlossenen System wird der Verbrauch des Monomeren volumetrisch verfolgt. Der Einflus verschiedener Reaktionsbedingungen auf die Polymerisation von α-Olefinen mit metallorganischen Mischkatalysatoren wird diskutiert. Die Methode bietet eine gute Reproduzierbarkeit und weist eine Fehlerbreite von maximal ± 4% auf. A simple apparatus to measuring the course of the polymerization of gaseous monomers is described; the consumption of the monomer is measured volumetrically in a closed system. Influence and variation of reaction conditions on the polymerization of…

Time and Temperature Dependence of Macro-ion-Macro-ester Equilibrium in the Cationic Polymerization of Tetrahydrofuran by HOSO2F

1977

Abstract Reactivity and equilibrium of two active species-tertiary oxonium ion (TOI) and superacid ester (SAE)-in the system of cationic polymerization of tetrahydrofuran (THF) initiated by fluorosulfonic acid (FSO3H) in dichloromethame has been studied. In the given system, it was found that TOI is mainly responsible for the polymerization at the initial stage; however, the cocentration of TOI decreases rapidly with the progress of polymerization and finally becomes almost untraceable. On the other hand, [SAE] monotonically increases as the polymerization proceeds. The stability of TOI appears less than that of SAE under the given reaction conditions. Results demonstrate that both the prog…

Carbocatalytic Oxidative Dehydrogenative Couplings of (Hetero)Aryls by Oxidized Multi‐Walled Carbon Nanotubes in Liquid Phase

2019

HNO3-oxidized carbon nanotubes catalyze oxidative dehydrogenative (ODH) carbon-carbon bond formation between electron-rich (hetero)aryls with O-2 as a terminal oxidant. The recyclable carbocatalytic method provides a convenient and an operationally easy synthetic protocol for accessing various benzofused homodimers, biaryls, triphenylenes, and related benzofused heteroaryls that are highly useful frameworks for material chemistry applications. Carbonyls/quinones are the catalytically active site of the carbocatalyst as indicated by model compounds and titration experiments. Further investigations of the reaction mechanism with a combination of experimental and DFT methods support the compet…

1987

ESR spectroscopic analyses of the deep-green solutions of living poly(2-isopropenylnaphthalene) [poly(2-IPN)] in THF at −80°C provided no evidence of the presence of radical anions as long as butyllithium (BuLi) was used as initiator. In contrast to this finding, radicals could indeed be detected if the polymerization was performed with metallic potassium in THF. These radicals were found to be only stable at low temperatures. UV/VIS spectra of solutions of 2-IPN in THF or toluene and of catalytic quantities of BuLi were recorded at temperatures between −45 and +20°C. On heating to >0°C, the colour of the deep-green solution changes irreversibly to reddish-brown, and this colour change is a…

Reversible Dimerization and Polymerization of a Janus Diradical To Produce Labile C−C Bonds and Large Chromic Effects

2016

Conducting polymers can be synthesized by irreversible diradical monomer polymerization. A reversible version of this reaction consisting of the formation/dissociation of σ‐dimers and σ‐polymers from a stable quinonoidal diradical precursor is described. The reaction reversibility is made by a quinonoidal molecule which changes its structure to an aromatic species by forming weak and long intermolecular C−C single bonds. The reaction provokes a giant chromic effect of about 2.5 eV. The two opposite but complementary quinonoidal and aromatic tautomers provide the Janus faces of the reactants and products which produces the observed chromic effect. A reaction mechanism is proposed to explain …

Electrochemical studies on organometallic compounds—xx. Electrogeneration of an unusual organometallic derivative of ruthenium(I)

1989

Abstract The two-electron reduction of dinuclear ruthenium complexes [RuCl 2 (η 6 - p -cymene)] 2 ( p -cymene = p -CH 3 C 6 H 4 CH(CH 3 ) 2 ] give the corresponding relatively stable ruthenium(I) dimer derivative. The same species can also be obtained by electrochemical reduction of the cationic complexes [(η 6 - p -cymene)Ru(μ-Cl) 3 Ru(η 6 - p -cymene)]PF 6 . A redox mechanism is proposed.

Study of the thermal behaviour of ordered bimetallic EDTA complexes

1986

Abstract The study of the thermal behaviour of a family of isostructural ordered bimetallic MM'(EDTA)·6H 2 O complexes has been performed using TG and DTA. Formal kinetic analysis of the dehydration step has been approached using non-isothermal procedures. The resulting correlation among the calculated E a values and the cationic sizes implies a common dehydration mechanism. Copper-containing complexes show distinctive behaviour during the ligand pyrolysis processes. A mechanistic interpretation involving formation of Cu(I) and Cu(0) intermediates is furnished. The evolution of the inorganic residues in systems containing both Co and Ni is especially considered given the interest in the (Co…