Investigation of oligomethylmethacrylate-lithium and its donor-acceptor complexes with organometal compounds by means of infrared spectroscopy

Anionic polymerization of methyl methacrylate in THF and toluene at ?70° was studied by means of i.r. spectroscopy. The reaction mixtures show characteristic absorption at 1600–1750 cm^?1 caused by the stretching vibrations of the propagating centre as well as by the groups obtained in side reactions (metal splitting, addition to a carbonyl group, cyclization). Sec-butyllithium is more effective in THF than n-butyllithium, ethyllithium and fluorenyllithium. When polymerizing in toluene, small amounts of a donor (THF or HMPT) cause formation of active centres similar to those in pure THF. The “living” ends of oligo-MMA form 1:1 complexes with electron acceptors such as trialkylaluminium and triethylboron.     

Electric conductivity of polybutadienyl- and polyisoprenyl-lithium in tetrahydrofurane and dimethoxyethane

The electric conductivity of polybutadienyl-lithium and polyisoprenyl-lithium has been investigated in tetrahydrofuran and dimethoxyethane solutions over wide temperature and concentration ranges (0 to ?70°; 7·10^?2 to 1·10^?7 and 5·10^?3 to 1·10^?7 mol/l). Dissociation constants, enthalpy and entropy of dissociation of ion pairs, relative constants for formation of ion triplets, and interionic distances were calculated for each system investigated. The nature of “living” chains under these conditions is considered.     

On the nature of the active centres in the anionic polymerization of methacrylonitrile—II. Initiation with organomagnesium compounds

It is shown by i.r. spectroscopy that the anionic polymerization of methacrylonitrile using organomagnesium compounds as initiators leads to two types of “living” ends i.e.

and

The active centres form complexes with the monomer, as well as with the nitrile groups of the monomer units in the polymer chain, in a hydrocarbon medium. The complexes are characterized by bands in the 2250–2280 cm^?1 region. Addition of donors destroys the complexes and in some cases (hexamethylphosphorous triamide) converts the complex of organomagnesium compound with monomer into a “living” end. In ethers as solvent, the dominant side-reaction is addition of the initiator to the nitrile group of the monomer.     

Changes in the electrochemical characteristics and u.v.-spectra of polydienyl-lithium chains on storage in polar media

The parallel changes in the electric conductivity and u.v. spectra of polybutadienyl- and polyisoprenyl-lithium (M_nLi) have been investigated in tetrahydrofuran and dimethoxyethane solutions during prolonged storage at 0 and 25°. A considerable dependence of the rate of these changes on the nature of the medium and M_n Li concentration was found. The decrease in the initiating activity during storage has been estimated for the PBLi-THF system.     

Crosslinked poly(ethylene oxide) modified with tetraalkylammonium salts as phase transfer catalyst

Radiation crosslinked poly(ethylene oxide)s (PEO) modified with two tetraalkylammonium salts: allyldimethyldodecylammonium bromide and ethylmethacrylate dimethyldodecylammonium bromide were prepared. They have been characterized by elemental analysis, IR, ¹H-NMR spectra, and DSC measurements. Their activity as phase transfer catalysts (PTC) in the model displacement reaction of 1-bromooctane with aqueous sodium cyanide were studied. The reaction kinetics were followed under pseudo-first-order conditions. Small amounts of onium salt inserted into the PEO network gave rise to a five time increase in the rate constant. The recovered catalysts could be re-used without loss of activity. © 1995 John Wiley & Sons, Inc.     

Novel reactive thermosensitive polyethers – control of transition point

A new class of thermosensitive polymers based on polyethers is discussed. Using living anionic polymerisation techniques a series of homo- and block copolymers of 2,3-epoxypropanol-1 (the glycidol), ethoxy ethyl glycidol ether, its hydrophobic derivative, and ethylene oxide of different molar masses and topology (linear and comb-like) was obtained. By simple chemical modification of hydroxyl groups in polyglycidol segments hydrophobic elements were introduced into polymer chains, which allowed to control the transition point related to the lower critical solution temperature between 0 to 100°C. The relation between the transition temperature and the structure of obtained polymers is discussed.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

IR-Spektren der Anion-Radikale von aromatischen Mononitrilen und Elektronenübergänge zwischen Anion-Radikalen und neutralen Molekülen

Zusammenfassung Es wurden die IR-Spektren (680–2500 cm^–1) der Anion-Radikale (AR) von Benzonitril, 1- und 2-Cyannaphthalin, 9-Cyanphenanthren, 4-Cyanbiphenyl, 1-Cyanpyren und 9-Cyan-anthracen gemessen, die aus den entspr. Nitrilen und metallischem Kalium in Tetrahydrofuran (THF) erhalten wurden. Die Umwandlung der Moleküle inAR führt zur Frequenzerniedrigung der nichtebenen C-H-Deformationsschwingungen im Bereich 700 bis 800 cm^–1. Die Valenzschwingungv _CN imAR liegt im Intervall 2080–2125 cm^–1, entsprechend der erniedrigten Bindungsordnung CN imAR Die IR-Spektren im Bereich 2000 bis 2250 cm^–1 wurden zur Untersuchung der Elektronenübergänge zwischenAR und den neutralen Molekülen der Nitrile benutzt. Die Richtung der Elektronenübergänge entspricht im allgemeinen der nach HMO-Methode errechneten Energien der niedrigsten antibindenden MO in den untersuchten Nitrilen.

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IR spectra of anion-radicals of aromatic mono-nitriles, and electron transitions between anion radicals and neutral molecules

The infrared spectra (680–2500 cm^–1) are measured of the anion-radicals (AR) of benzonitrile, 1- and 2-naphthalenecarbonitriles, 9-phenanthrenecarbonitrile, 4-biphenylcarbonitrile, 1-pynitriles, 9-phenanthrenecarbonitrile, 4-biphenylcarbonitrile, 1-pyrenecarbonitrile and 9-anthracenecarbonitrile, obtained on treating the initial nitriles with metallic potassium in tetrahydrofuran. The formation of theAR leads to a decrease of the out-of-plane C–H frequencies in the region 700–800 cm^–1. The nitrile frequencies of theAR is observed in the region 2080 to 2125 cm^–1, which is in agreement with the decreased order of the CN bond (HMO). The IR-Spectra in the interval 2000 to 2250 cm^–1 are used in the study of the electron transitions between theAR and the nitrile molecules. The electron transitions in the examined nitriles are in general agreement with the energies of the first antibonding orbitals, calculated by HMO.

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Mit 8 Abbildungen