Ivan M. Panayotov

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

ZusammenfassungEs 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 ValenzschwingungvC≡N imAR liegt im Intervall 2080–2125 cm−1, entsprechend der erniedrigten Bindungsordnung C≡N 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.AbstractThe 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 C≡N 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.

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

Abstract 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.

On the nature of the active centres in the initial stages of methacrylonitrile anionic polymerization—I: Spectral studies

Abstract The active centres in the initial stage of methacrylonitrile anionic polymerization have been studied by means of electronic and i.r.-spectra as well as by use of model compounds. The attachment of the first monomer unit to the initiator causes formation of the carbanion , characterized by an absorption band at 2020–2055 cm −1 . Addition of more monomer units leads to the appearance of a new band at 2100 cm −1 , due to the group . The appearance of a new band at 2260 cm −1 and the shift of the band at 2020–2055 cm −1 towards higher frequencies, as the number of adjacent monomer units is increased, is explained by interaction of the active centres with the nitrile groups of the polymer chain.

Investigation by means of I.R. spectroscopy of styrene oligomers containing acrylonitrile active ends

Abstract The successive addition of acrylonitrile (AN) portions to oligostyrene anionic ends was studied by means of i.r. spectroscopy. The attachment of AN to the oligostyrene active centre took place mainly across the double bond of the monomer accompanied by formation of the carbanion CHCN with characteristic absorption band at 2030–2040 cm−1. Comparatively high temperatures of the experiments (above −40°) provided conditions for side reactions in the polymerization. The latter were checked spectrophotometrically: cyclization according to Ziegler-Thorpe and formation of anionic centre and proton transfer reaction between this centre and AN causing the formation of enaminonitrile structure. By study of model compounds, the band at 2110–2130 cm−1 was assigned to the group.

Interactions of ligands with lithium picrate in dioxane

The interaction of several cyclic ethers, poly(ethylene glycol dimethyl ether)s, nitriles, esters and ketones with lithium picrate in dioxane at 25°C was investigated by means of a competition method using cross-linked poly(ethylene oxide) (PEO) as the insoluble ligand. The Langmuir-Klotz isotherm of LiPi binding to the PEO gel gave an apparent binding constant, K′, as a function of the concentration of added ligand. Plots of 1/K′ vs. the ligand concentration then yielded the formation constant, KL, of the ligand complex with LiPi. The results demonstrate that in dioxane one ligand molecule binds to LiPi. While there is some dependence on the Gutmann donicity number of the respective ligands, steric factors often play a dominant role in determining the value of KL. The results were compared with complexation data obtained on similar systems but by different methods.

Synthesis and Some Properties of Graft Copolymers with Uniform Polyoxyethylene Side Chains

Abstract Graft copolymers with uniform polyoxyethylene (PEO) side chains were synthesized by transesterification of poly(methyl, ferf-butyl fumarate) (PMtBF) or poly(methyl, tert-butyl fumarate-co-styrene) poly-(MtBF-co-St) with potassium alkoxide of PEO monoether. The grafting efficiency increased with enhanced alkoxide reactivity, but the main factor in the ester exchange proved to be the structure of the backbone. This effect was ascribed to the thermodynamic incompatibility between fumaric polymers and PEO. The polymers were characterized by spectral methods, GPC, and DSC. In THF the graft copolymers comprising a polyfumarate backbone with PEO side chains eluted at higher elution volumes than did the backbone homopolymers. In benzene their intrinsic viscosities were lower than those of the backbones. In aqueous eluents, micelles were detected, and their aggregation number depended on the composition of the copolymer and the eluent.

Poly(ether-ester) networks prepared by polycondensation of R,S-malic acid with diols and polyether alcohols in the presence of N,N′-dicyclohexylcarbodiimide

Abstract The possibility of preparing polyester and poly(ether-ester) networks from R,S-malic acid and diols or poly(ether alcohol)s by polycondensation was investigated. The reactions were carried out in tetrahydrofuran in the presence of N , N ′-dicyclohexylcarbodiimide and p -toluenesulfonic acid and pyridine as catalyst. I.r., 1 H n.m.r. and mass spectra of the crosslinked products obtained, confirmed their ester and ether-ester structure. The dependence of swelling and some thermodynamic parameters upon the kind of alcohol used was established. The new synthesized crosslinked polymers, which can be swelled in a variety of solvents and are thermohydrolytically unstable, can be used as biodegradable carriers for drugs and microelements.

Mechanism of the anionic polymerization of lactones, initiated by intercalation graphite compounds

SummaryThe anionic polymerization of β-propiolactone (PL)oxethane-2-one, pivalolactone (PVL) — 3,3-dimethyloxethane-2-one and ɛ-caprolactone (CL) — oxepane-2-one, initiated by binary and ternary intercalation compounds (IC) of lithium and potassium in graphite is investigated. The polymerization is carried out in bulk or in xylene. It is established that the lactones penetrate in IC and polymerize in their interlayer spacings. The polymerization causes a delamination of IC. High polymers of the lactones can be obtained by the action of some IC investigated.

Über die Reduktionsformen einiger nichtenolisierenden aromatischer Ketone und Chinone, welche die Vinylpolymerisation zu initiieren vermögen

ZusammenfassungBekanntlich lösen die Reduktionsformen aromatischer Carbonylverbindungen (ACV) eine anionische Polymerisation von Vinylmonomeren aus. Das Vermögen der Reduktionsformen vonACV, den mit ihnen in Wechselwirkung tretenden Molekülen ein Elektron zu übertragen, wird von der Elektronenaffinität beider Partner bestimmt. Um Angaben bezüglich der Elektronenaffinität zu ermitteln, wurden die Potentiale der polarographischen Reduktion gemessen und mit den nach derHückel-Methode berechneten Energiewerten des niedrigsten antibindenden Molekülorbitals korreliert. Für eine Reihe strukturell verwandter Verbindungen wurde eine lineare Abhängigkeit zwischen den Halbstufenpotentialen der polarographischen Reduktion und des niedrigsten antibindenden Molekülorbitals gefunden. Die so erhaltene Reihe stimmt mit einer bereits früher aufgestellten überein.Auf Grund quantenmechanischer Berechnungen und der gemessenen polarographischen Halbstufenpotentiale derACV wurden die Änderungen der Freien Enthalpie, die Enthalpie-Änderung und die Gleichgewichtskonstante des Überganges eines Elektrons von der Reduktionsform zum Monomeren ermittelt. Ferner wurde der Zusammenhang zwischen Initiierungsvermögen der Reduktionsformen vonACV und der Elektronenaffinität diskutiert.AbstractIt is known that the reduction forms of aromatic carbonyl compounds (ACC) initiate anionic polymerization of vinyl monomers. The ability of the reduction forms to transfer an electron to the interacting molecules is defined also by the electron affinity of the partners. To obtain data about the electron affinity the half-wave potentials of polarographic reduction were measured and compared with the values of the lowest antibonding molecular orbital, according to theHückels method.A linear correlation between the potentials of polarographic reduction and the energy of the lowest antibonding molecular orbit was found.The results prove the correctness of the previously determined electroaffinity defined by electron transfers between the reduction forms and neutral molecules.From the data of quantum chemical calculation and the polarographic reduction ofACC the changes of the free energy, enthalpy and the equilibrum constant for electron transfer reaction were calculated. The initiation ability of the reduction forms ofACC and the elctron affinity discussed.

Influence of the polyether chain on the dissociation of “living” polymers obtained in the anionic polymerization of ethylene oxide☆

Abstract Conductivity studies were carried out on block copolymers of composition K + , −(EO) n - α MeSt-(St) x - α MeSt-(EO) n − , K + , where n = 1–5 or 20, in THF. The conductivity of the solutions exhibits a strong tendency to increase as n is raised up to 3, and to change only slightly on further extension of the polyether chain. An equilibrium between ion pairs and free ions is established in the solution only when n is 1 or 2; for n ⩾ 3, ion triplets are formed also. The dissociation constants for the ion pairs and the ion triplets and their temperature dependence were determined. The formation of ion triplets, as well as the changes in dissociation of the ion species on extending the polyether block, are explained by solvation of the counter-ion by the polyether chain.