Dynamic shear modulus in the splitting region of poly(alkyl methacrylates)

A systematic study of the dynamic shear modulusG ^*=G+G in three poly(alkyl methacrylates) (PEMA, PnPMA, PnBMA) at frequencies between 0.001 and 500 rad/s is presented. As the splitting frequencies _s are low, aging effects can be observed in the splitting region. There is a systematic shift of the splitting frequency _s to lower values with increasing length of the alkyl side group. In PnBMA a separate shear appearance is observed about two frequency decades below the local mode . This is discussed in terms of the concept of minimal cooperativity. Aging effects are: Shift of the maximum loss frequency to lower values, peak sharpening of the relaxation, and intensity changes of and . These effects are discussed in terms of the sequential aging concept. Aging leads to a pronounced bending of the traces upwards from the equilibrium line in the Arrhenius diagram. These non-equilibrium phenomena are promoted by the small slope m=d(log )/dT of the trace in the splitting region.Dedicated to Prof. E. W. Fischer at the occasion of his 65th Birthday Lieber Herr Fischer, die Hallenser Polymerphysiker danken Ihnen aufrichtig für die warmherzige und effektive Förderung der Polymerwissenschaften im Raum Halle-Merseburg.     

On the thermal analysis of mineral components in clays

The paper deals with the problem of the interactions of the mineral components in clay and argillite samples during the thermal analysis. It is shown that depending on the experimental conditions, the interaction of pyrite and carbonates may cause atypical course of DTA and TG curves. Also the common occurring of sylvine and halite shifts the temperature of their melting to a lower value and this phenomenon occurs in pure salts as well as in the great dilution to some percent in clays.

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Zusammenfassung Es wird über Zwischenreaktionen der mineralischen Komponenten von Ton und Argillit während der thermischen Analyse berichtet. Von den Versuchsbedingungen abhängend produzieren die Zwischenreaktionen von Pyrit und Karbonat DTA und TG Kurven deren Verlauf nicht charakteristisch ist. Das gemeinsame Vorkommen von Sylvin und Halit verschiebt ihren Schmelzpunkt in Richtung der niedrigen Temperaturen in reinen Salzen ebenso wie bei großer Verdünnung von einigen Prozenten in Ton.

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Résumé Les interactions des constituants minéraux des échantillons d'argile et d'argilite pendant l'analyse thermique ont été examinées. Suivant les conditions expérimentales, l'interaction de la pyrite et des carbonates peut provoquer un tracé des courbes ATD et ATG qui s'écarte de l'allure type. La présence simultanée de sylvine et d'halite produit un abaissement de leur point de fusion et ce phénomène apparaít aussi bien avec les sels purs qu'avec ceux fortement dilués, à raison de quelques pour cent, dans les argiles.

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, , ., () (). . , .

     

Liquid phase CO+H2 reactions in presence of ruthenium catalysts

Several effects on the hydrogenation of carbon monoxide in propanol in presence of ruthenium catalysts are examined. The homologation reaction is not observed, only propyl formate and propyl acetate are produced with any ruthenium catalyst. The pH-value is an important parameter: in acid media, the yield of propyl formate is noticeably increased indicating different catalytic active species. The addition of cesium salts is also benefitial for formate formation. This is not the case when water is associated with propanol as solvent. Finally, no ethylene glycol is detected. The process is found to be homogeneous and methanol seems to be the precursor of methyl formate.

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, . , . : , . . , . . , -, .

     

Untersuchung des Zerfalls verschiedener Azoinitiatoren in Lösung

The decomposition of various symmetric and unsymmetric azo-initiators (1,1-dichloro-1,1-diphenyl-1,1-azoethane, 2,2-dichloro-2,2-azopropane, 1,1-dichloro-1,1-azocyclohexane, 2,2-diacetoxy-2,2-azopropane, 1,1-diacetoxy-1,1-diphenyl-1,1-azoethane, 1,1-diacetoxy-1,1-azocyclohexane, 2,2-dipropionoxy-2,2-azopropane, 2,2-dicapronoxy-2,2-azopropane, 4,4-dimethyl-1,4-azobutyrolactone, azoisobutyronitrile, 2-t-butylazo-2-cyanobutan, 2-t-bytylazo-1-cyanocyclohexan) in solution was studied in dependence of temperature. Volumetry and differential-scanning-calorimetry (DSC) were used to determine decomposition rates; first order kinetics was found in all cases.

     

ESR and ENDOR Investigations on Various <Emphasis Type="Italic">Wurster</Emphasis>’s Radical Cations in Solution. Experimental Results,Theoretical <Emphasis Type="Italic">Ab Initio</Emphasis>, and DFT Calculations

Summary. ESR and ENDOR spectra are reported of several symmetrical substituted N,N,N,N-tetraalkyl-p-phenylenediamine radical cations in solution. Different N,N-alkyl substituted para-phenylenediamines, like the ethyl, n-propyl, and iso-propyl derivative are compared with the parent N,N,N,N-tetramethyl-p-phenylenediamine (Wursters Blue Cation). N,N,N,N-Tetrabenzyl-p-phenylenediamine, 1,4-dipyrrolidinylbenzene, and N,N-bis[4-(dimethylamino)phenyl]piperazine are additionally investigated. Experimental and calculated hyperfine coupling constants are compared. Characteristic UV-VIS data and redox potentials in acetonitrile are reported, together with the syntheses of the compounds.     

N-methyI-N-(triethoxysilylmethyl) andN-methyl-N-(silatran-1-ylmethyl) substituted glycine and alanine

Organosilicon derivatives of glycine, - and -alanine, and -methylalanine were prepared by the reaction of methyl esters of - and -halocarboxylic acids withN-methylaminomethyltriethoxysilane in the presence of triethylamine. The compounds synthesized were converted into the correspondingN-silatran-l-ylmethyl derivatives. Trimethylsilyliodoacetate reacts withN-methylaminomethyltrietoxysilane to give 2,2-diethoxy4-methyl-1-oxa-4-aza-2-silacyclohexane-6-one. Its reaction with triethanolamine leads toN-methyl-N-(silatran-l-ylmethyl)glycine.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 341–343, February, 1995.     

Catalyst deactivation in toluene steam dealkylation

Two deactivation factors of Rh/-Al₂O₃ catalysts in toluene steam dealkylation are examined: deactivation during working and sulfur poisoning. Onstream deactivation is only due to coke deposit. Specific activity per free exposed fraction of the metal is constant. Sulfur is a strong non-selective poison which may hinder coke formation.

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Rh/-Al₂O₃ : . . . , .

     

Steroid compounds from the Pacific starfishesLuidia quinaria andDistolasterias elegans

One new and four previously known steroid compounds were identified from the Pacific starfishesLuidia quinaria andDistolasterias elegans. The structure of the new steroid was established from spectral data and chemical correlations with other steroids such as 5-cholestane-3,5,6,15,16,26-hexaol 3-sulfate (1). The previously known compounds were identified as 5-cholestane-3,5,6,15,26-pentaol 15-sulfate (2) fromLuidia quinaria and sodium (24S)-O-(-d-giucopyranosyll-5-cholestane-3,6,8,15,24-pentaol 6-sulfate (3), sodium (24S)-5-cholestane-3,6,8,15,24-pentaol 24-sulfate (4), and sodium tornasterol A sulfate (5).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 473–476, February, 1996.     

Kinetics of the catalytic transformation of isobutene into methacrylonitrile with NO on supported nickel oxide aerogel

Kinetic studies of the nitroxidation of isobutene by NO show that the reaction follows a redox mechanism in the temperature range of 300–400°C. This mechanism implies an interaction between dehydrogenated isobutene -allyl radical and atomic nitrogen due to the decomposition of NO by the reduced catalyst, which is then reoxidized.

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NO , 300–400°C. - , NO , .

     

Differential thermal analysis of potassium perchlorate

A study has been made of the differential thermal analysis of (i) potassium perchlorate in powdered form, (ii) potassium perchlorate in pelletized form, (iii) potassium perchlorate recrystallized from liquid NH₃, and (iv) potassium perchlorate preheated for 24 hours at 375°. Pretreatment of potassium perchlorate leads to a desensitization of both endothermic and exothermic processes. Additionally, the pretreatment tends to convert the symmetric exotherm into an asymmetric exotherm due to merging of the two exotherms. An analysis of the factors causing asymmetry in the exotherm has thrown fresh light on the mechanism of thermal decomposition of potassium perchlorate.

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Zusammenfassung Eine differentialthermoanalytische Untersuchung wurde an, (i) Kaliumperchlorat in Pulverform, (ii) Kaliumperchlorat in pelletisierter Form, (iii) Kaliumperchlorat, umkristallisiert aus flüssigem Ammoniak und (iv) Kaliumperchlorat, 24 Stunden bei 375° vorgeheizt, durchgeführt. Die Vorbehandlung von Kaliumperchlorat führt zu einer Verdichtung sowohl der endothermen als auch der exotherman Vorgänge. Ausserdem führt die Vorbehandlung zur Umwandlung der symmetrischen Exotherme in eine asymmetrische Exotherme durch Vereinigung der zwei Exothermen. Die Analyse der die Asymetrie der Exothermen verursachenden Faktoren zeigte den Mechanismus der thermischen Zersetzung des Kaliumperchlorats unter neuen Gesichtspunkten.

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Résumé On a effectué l'étude par analyse thermique différentielle du perchlorate de potassium: (i) en poudre, (ii) sous forme comprimée, (iii) recristallisé dans NH₃ liquide, (iv) préchauffé à 375° pendant 24 heures. Le traitement préalable du perchlorate de potassium entraîne la désensibilisation des processus endothermiques et exothermiques. De plus, le traitement préalable tend à convertir l'exotherme symétrique en un exotherme asymétrique, du fait de la fusion des deux exothermes. Une analyse des facteurs causant l'asymétrie de l'exotherme a donné une vue nouvelle du mécanisme de la décomposition thermique du perchlorate de potassium.

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, , , 375° 24 . . , , . , , .

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This work has been supported by a grant from the Indian Space Research Organization (I.S.R.O). It also includes financial support to one of the authors (D. S.). This support is gratefully acknowledged.     

Modification of the sorption kinetic characteristics of natural zeolite adsorbents used in pressure swinging adsorption operations

The adsorption kinetic characteristics of natural zeolite based adsorbents can be improved significantly by grinding, size fractionation and regranulation. The sorption characteristics of such materials with tridisperse pore-size distributions are discussed here. (Tridisperse structure: the holes of crystallites, the macropore system among crystallites and macropores produced by granulation.)

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- , . .

     

Catalytic deamination on solid surfaces part 2.-Deamination of dicyclohexylamine on aluminium oxide

Deamination of dicyclohexylamine gives the same final products as those obtained from the respective primary amine on a similar surface. A theoretical rate equation derived permits the calculation of various rate constants from the experimental data. It is concluded that one of the intermediates formed from the two amines must be identical.

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, . . , , , .

     

Synthesis of some 5′-O-amino acid derivatives of uridine as potential inhibitors ofUDP-glucuronosyltransferase

Summary In an attempt to develop potential inhibitors ofUDP-glucuronosyltransferase, some 5-O-amino acid derivatives of uridine were synthesized. N-protectedL-amino acids were coupled at the 5-O-position of 2,3-O-isopropylideneuridine by esterification employing the method of symmetrical anhydrides in presence of 4-dimethylaminopyridine, 5-O-(N-benzyloxycarbonyl-O-tert.butyl-L-threonl)-23-O-isopropylideneuridine (1), 5-O-(N-tert.butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylideneuridine and (2), 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (3), and 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (4) were obtained in good yield after column chromatography on silica gel. The treatment of2 withTFA/CH₂Cl₂ (6:1) at room temperature for 30 min led to a selective removal of theBoc group without deblocking of the 2,3-O-isopropylidene group of uridine. Treatment of2 withTFA/H₂O (5:1) at room temperature for 1 h, however, released bothBoc and 2,3-isopropylidene groups. TheZ group of1 was deprotected by catalytic hydrogenolysis over 10% Pd/C/ammonium formate.

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Synthese von 5-O-Aminosäurederivaten des Uridins als potentielle Inhibitoren derUDP-Glukuronosyl-Transferase

Zusammenfassung In einem Versuch, potentielle Inhibitoren derUDP-Glukuronosyl-Transferase zu entwickeln, wurden einige 5-O-Aminosäurederivate des Uridins synthetisiert. N-GeschützteL-Aminosäuren wurden durch Veresterung mit der 5-O-Position des 2,3-isopropylidenuridins gekuppelt (Methode der symmetrischen Anhydride in der Gegenwart von 5-Dimethylaminopyridin). Solcherweise wurden 5-O-(N-Benzyloxycarbonyl-O-tert.butyl-L-threonly)-2,3-O-isopropylidenuridin (1), 5-O-(N-tert.Butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylidenuridin (2), 5-O-(N-tert.Butyloxycarbonyl-L-leucyl)-2,3-O-isopropylidenuridin (3) und 5-O-(N-tert.Butyloxycarbonyl-L-valyl)-2,3-O-isopropylidenuridine (4) nach Säulenchromatographie (Kieselgel) in guter Ausbeute hergestellt. Die Behandlung von2 mitTFA/CH₂Cl₂ (6:1) bei Zimmertemperatur (30 min) führte zu einer selektiven Abspaltung derBoc-Gruppe ohne Deblockierung der 2,3-O-Isopropylidengruppe des Uridins. Eine Behandlung von2 mitTFA/H₂O (5:1) bei Zimmertemperatur für 1 Stunde führte hingegen zur Abspaltung sowohl derBoc als auch der 2,3-O-Isopropylidengruppe. DieZ-Gruppe von1 wurde durch katalytische Hydrogenolyse auf 10% Pd/C/Ammoniumformiat abgespalten.

     

Influence of o-benzoquinone nature on initiation of radical polymerization by the o-benzoquinone—tert-amine system

o-Benzoquinones initiate radical polymerization of methacrylates under visible light irradiation in the presence of tertiary amines. Spectral sensitivity of the initiating system coincides with absorption bands of o-benzoquinone attributed to the S(*) (_max 400 nm) and S(n*) (_max 600 nm) transitions. The amine radicals (Am^·) initiating polymerization are generated by the photoreduction of Q in the presence of AmH from the triplet radical pair ³(QH^·, Am^·). The yield of Am^· depends on the difference between the volumes of substituents in the 3 and 6 positions of the quinoid ring and is maximal for symmetrically substituted o-benzoquinones. For a series of derivatives of symmetrical 3,6-di-tert-butyl-o-benzoquinone, the rate of photopolymerization of ,-bis(methacryloyloxyethyleneoxycarbonyloxy)ethyleneoxyethylene (OCM-2) in the presence of N,N-dimethylaniline is determined by the free energy (G _e) of electron transfer from the amine to photoexcited o-benzoquinone. The G _e value includes the energies of oxidation of the amines and reduction of the o-quinones and the energy of the 00 transition of the triplet excited state of o-benzoquinones, which are equal to their redox potentials. The photopolymerization rate is maximal for G _e 0.     

Concerning the absorption and emission properties of phenanthro[1,10,9,8,o,p,q,r,a]perylene-7,14-dione

Summary In contrast to hitherto published data, phenanthro[1,10,9,8,o,p,q,r,a]perylene-7,14-dione, the fundamental chromophoric system of hypericin type compounds, exhibits an absorption with a long wavelength band at 423 nm in aprotic solvents like dimethylsulfoxide (7000). Its fluorescence in these solvents is below the detection limit. In protic solvents like methanol, the long wavelength absorption is bathochromically shifted to 546 nm, and a fluorescence at 565 nm is observed. This behavior was interpreted from the reversal ofn – * and – * transitions. The data have not been recorded yet due to the very low solubility of this compound. Its monoprotonation in ground and excited states is characterized bypK _a andpK* _a values of –6 and 2; diprotonation occurs at apK _a=–7.

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Absorptions- und Emissions-Eigenschaften von Phenanthro[1,10,9,8,o,p,q,r,a]perylen-7,14-dion (Kurze Mitt.)

Zusammenfassung Im Gegensatz zu bislang publizierten Daten zeigt Phenanthro[1,10,9,8,o,p,q,r,a]perylen-7,14-dion, das fundamentale chromophore System der Hypericintyp-Verbindungen, in aprotischen Lösungsmitteln wie Dimethylsulfoxid eine Absorption mit einer langwelligen Bande bei 423 nm (7000). In diesen Lösungsmitteln ist Fluoreszenz nicht nachweisbar. In protischen Lösungsmitteln wie Methanol wird die langwellige Bande bathochrom verschoben (546 nm) und bei 565 nm tritt Fluoreszenz auf. Dieses Verhalten wurde mit der Umkehr in der Reihenfolge vonn – * und – * Übergängen interpretiert. Die Daten wurden wegen der extremen Schwerlöslichkeit dieser Verbindung bislang nicht erhalten. Die Monoprotonierung im Grund- und Anregungszustand ist durchpK _a- undpK* _a -Werte von –6 und 2 charakterisiert; die Diprotonierung tritt beipK _a=–7 ein.

     

Kinetics of oxidation of water by Mn(IV) sulfate in acid media

Kinetics of the Mn(IV)Mn(III) transition in the oxidation of watet to O₂ was investigated at 60–100°C in 6–15 M H₂SO₄. The reaction is approximately 2-nd order in Mn(IV) concentration in the process of oxidation and 1-st order in initial Mn(IV) concentration. The kinetics is interpreted by the existence of dimeric forms Mn(IV)·Mn(IV), Mn(IV)·Mn(III) and Mn(III)·Mn(III). The suggested mechanism includes O₂ formation directly in the coordination sphere of the Mn(IV)·Mn(IV) dimer in a polyelectronic process.

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Mn (IV)»Mn (III) O₂ 60–100°C 6–15 M H₂SO₄. Mn (IV) I- Mn (IV). [Mn (IV)]₂; [Mn(III)]₂ Mn(IV)·Mn (III). , [Mn (IV)]₂

     

TheT 1 state ofp-nitroaniline and related molecules: A CNDO/S study

The nature of the lowest energy triplet state (T ₁) ofp-nitroaniline (PNA), N,N-dimethyl-p-nitroaniline (DMPNA) and nitrobenzene (NB) is reexamined using the semiempirical CNDO/S-CI method with selected parameter options. The present results indicate that in the case of theunperturbed molecules the short-axis polarized * n() triplet largely localized at the acceptor end of the molecule may lie lower in energy than the triplet manifold counterpart of the intense intramolecular charge-transferD ⁺ A ^–singlet excitation. Computations suggest, however, that polar solvents strongly stabilize the PNA and DMPNA * charge-transfer triplet relative to other excitations, whereas specific solvent hydrogen-bonded interactions stabilize the * n() triplet of NB below those of * character. These assignments allow a rationalization of phosphorescence lifetime data,T _n T ₁ absorption measurements and relative photochemical behavior.