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  • 1990-1994  (3.578)
  • 1980-1984
  • 1991  (3.578)
  • Polymer and Materials Science  (3.577)
  • Nuclear reactions
Materialart
Erscheinungszeitraum
  • 1990-1994  (3.578)
  • 1980-1984
Jahr
  • 101
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 1-10 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Experimental methods for comparing the reactivities of unsaturated substances towards the benzoyloxy radical are considered. Results for various monomers are discussed. It is shown that some substances show high reactivity towards the radical although they do not ordinarily give homopolymers or act as comonomers; they include β-methylstyrene, stilbene and related substances, and 1.4-diphenylbuta-1, 3-diene.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 102
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The introduction of mesogenic groups in main- and sidechains of epoxy thermosets results in an ordered multiphase network with cellular structure, if gelation occurs below the maximal cure temperature Tmax. Tmax is individual for a given combination of monomers. The multiphase network consists of relatively soft anisotropic cell nuclei and hard isotropic cell walls. If gelation occurs above Tmax single phase networks are obtained. The size of the cell nuclei strongly depends on the used monomers and varies up to two orders of magnitude. The multiphase structure was found to have no impact on the tensile elastic modulus.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 103
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 43-50 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The polymerisation of styrene and methylacrylate initiated by hydroperoxides is accelerated in the presence of strong acids such as sulfuric acid, p-toluene-sulfonic acid or perchloric acid. By copolymerising styrene and methylmethacrylate and by phenolic type inhibitors the radical nature of the catalytic effect of the acid was proved. Kinetic experiments demonstrated the acid involvement in the starting reaction.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 104
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 11-21 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: By modification of the resin matrix and by additives unsaturated polyesters result in materials with a large variety of properties. The mechanical values can be tailor-made by chemical modification of the polymer chain or rubber-like additives. Antistatic properties and electrical conductivity can be achieved by addition of carbon black, graphite or metallic fillers. Furthermore the thermal conductivity can be influenced. Other fillers improve the friction and wear behaviour or lead to a significant reduction of weight when microspheres are added. The tailored modification of properties effectively contributes to meet higher security requirements.
    Notizen: Ungesättigte Polyester ergeben durch Modifizierung der Harzkomponente oder durch Additive Werkstoffe mit einem breiten Eigenschaftsprofil. Die mechanischen Werte sind durch chemische Modifikation der Polymerkette oder durch kautschukartige Additive gezielt einstellbar. Antistatische Eigenschaften und elektrische Leitfahigkeit lassen sich durch Zugabe von Rußen, Graphit oder metallischen Füllstoffen erreichen. Gleichzeitig kann auch die Wärmeleitfähigkeit beeinflußt werden. Andere Füllstoffe verbessern das Reibungs- und Verschleißverhalten oder können bei Zugabe von Mikrohohlkugeln zu deutlicher Gewichtsverminderung führen. Die gezielte Veränderung der Eigenschaften trägt wesentlich zum Einhalten erhöhter Sicherheitsanforderungen bei.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 105
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 23-32 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Duroplastische Formmassen werden nach konventionellen Verfahren der Kunststofformgebung wie Formpressen und Spritzgießen bzw. deren Varianten Spritzpressen und Spritzprägen verarbeitet. Wie in anderen Industriezweigen hat auch hier der wachsende Kostendruck zu einer steten Weiterentwicklung dieser Verfahren geführt. Über erfolgreiche Verfahrensverbesserungen zur Reduzierung der Herstellkosten wird im folgenden berichtet.Die Einführung der Spritzgießverarbeitung für Duroplaste in den 60er Jahren bedeutete gegenüber der bis dahin ausschließlich betriebenen Preßverarbeitung einen erheblichen Rationalisierungsschritt. Die Zykluszeiten ließen sich durch das Aufschmelzen der Formmasse in der Plastifiziereinheit sowie durch das Einbringen von Friktionswärme beim Einspritzvorgang erheblich reduzieren. Heute erlebt die Preßverarbeitung eine Renaissance insbesondere dann, wenn es gilt, hochpräzise Formteile mit minimaler Schwindung und geringstem Verzug herzustellen. Durch Rundtischautomaten, Vorplastifiziergeräte und Entnahmegeräte ließen sich die wirtschaftlichen Nachteile der klassischen Preßverarbeitung weitgehend kompensieren.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 106
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 51-60 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: The crystallization and solidification behaviour of polyamides are influenced by additives such as nucleating agents or fillers. During processing morphological structures are obtained which affect the shrinkage, linear thermal expansion and dimensional changes due to water absorption. By studying the change of volume after water absorption, the dimensional change in length, breadth and thickness are easily understood.
    Notizen: Additive in Polyamiden wie Nukleierungsmittel oder Verstärkungsmittel beeinflussen das Kristallisations- und Erstarrungsverhalten. Während der Herstellung von Probekörpern bilden sich morphologische Strukturen, die die Verarbeitungsschwindung, den linearen Ausdehnungskoeffizienten und die Dimensionsänderung während der Wasseraufnahme beeinflussen. Anhand der Volumenänderungen wird der Zusammenhang zwischen der Wasseraufnahme und der Dimensionsänderung in allen drei Raumrichtungen verständlich dargestellt.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 107
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 75-86 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Poly(2,6-dimethyl-1,4-phenylene oxide) with exactly one functional endgroup was synthesized by oxidative polymerization, halogen substitution polymerization, and by phase transfer catalysis. Reaction with 4-vinylbenzoyl chloride resulted in a quantitative conversion to a macromonomer as shown by GPC and endgroup analysis. The macromonomer is a glassy material with a Tg from 150 to 190°C depending on the molecular weight.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 108
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die Eigenschaften von Poly[1-(2-hydroxyethyl) aziridin] wurden im Hinblick auf die Komplexbildung für die Metalle Co(II), Zn(II), Ni(II), Cu(II), Cr(III), Fe(III), Cd(II), Pb(II) und Sr(II) in wäßriger Lösung untersucht. Die LPR-Methode beruht auf der Retention von anorganischen Ionen durch lösliche Polymere in einer Membran-Filtrationszelle und nachfolgender Abtrennung der niedermolekularen Anteile vom gebildeten Polymerkomplex. Die Wechselwirkung des hydrophilen Polymeren wurde als Funktion von pH und Filtrationsfaktor bestimmt. Nach dem erhaltenen Wechselwirkungsmuster bildet Cu(II) die stabilsten Komplexe mit dem Polyaziridin innerhalb des pH-Bereiches von 3 bis 7. Bei pH 3 ist es möglich, Cu(II) von allen anderen Metallionen zu trennen. Sr(II) wird im ganzen untersuchten pH-Bereich nur schwach retentiert. Bei pH 7 traten alle Metalle, außer Sr(II), mit dem Polymeren in Wechselwirkung und wurden nahezu quantitativ retentiert.
    Notizen: The metal complexing properties of poly[1-(2-hydroxyethyl) aziridine] for the metals Co(II), Zn(II), Ni(II), Cu(II), Cr(III), Fe(III), Cd(II), Pb(II), and Sr(II) in aqueous phase were investigated. The LPR method is based on the retention of inorganic ions by soluble polymers in a membrane filtration cell and subsequent separation of low-molecular species from the polymer complex formed. The metal interaction with the hydrophilic polymer was determined as a function of pH and filtration factor. According to the interaction pattern obtained, Cu(II) forms the most stable complexes with the polyaziridine within the pH range 3 to 7. At pH 3, it is possible to separate Cu(II) from all other metal ions. Sr(II) is only slightly retained at the pH range investigated. At pH 7, all elements, except Sr(II), did interact with the polymer and were almost quantitatively retained.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 109
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 1-10 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Eine neue Klasse von Urethan-Acrylat-Monomeren wurde durch Umsetzung von Diisocyanaten wie Toluylendiisocyanat (TDI) und Hexamethylendiisocyanat (HMDI) mit Hydroxyethylmethacrylat oder Hydroxypropylmethacrylat und gesättigten Alkoholen wie Stearylalkohol oder Decanol hergestellt und durch IR- und NMR-Spektroskopie charakterisiert. Durch radikalische Polymerisation dieser Monomeren wurden Acrylatpolymere mit Urethanseitengruppen erhalten, die IR-spektroskopisch, viskosimetrisch und thermisch charakterisiert wurden.Die thermodynamischen Parameter des Polymerabbaus wurden berechnet; ein möglicher Abbaumechanismus wird vorgeschlagen.
    Notizen: A new class of urethane-acrylic monomers was synthesized from diisocyanates such as toluylene diisocyanate (TDI) and hexamethylene diisocyanate (HMDI), unsaturated alcohols like hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), and saturated alcohols such as stearly alcohol and decanol. The monomers were characterized by IR and NMR spectroscopy. Urethane pendent acrylic polymers, obtained by polymerizing these monomers, were characterized by IR, solubility viscosity, and thermal studies. The thermodynamic parameters for the degradation were calculated and a probable degradation mechanism is proposed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 110
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 33-39 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Durch Umsetzung von Rizinusöl mit Toluylen-2,4-diisocyanat, Hexamethylendiisocyanat, Isophorondiisocyanat oder 4,4′-Diphenylmethandiisocyanat wurden Polyurethan-Präpolymere erhalten, die mit einem Epoxidharz aus Bisphenol-F und mit 1,3-Diaminopropan als Härter in Aceton homogen gemischt wurden. Mit diesen Mischungen getränkte Glasfasermatten wurden in einer Presse ausgehärtet; die Lösungsmittelbeständigkeit, elektrische Eigenschaften, Biegefestigkeit, Izod-Schlagfe-stigkeit und Rockwell-Härte der so erhaltenen Laminate wurde bestimmt. Die Abhängigkeit der elektrischen Leitfähigkeit σ von der Temperatur folgt der empirischen Gleichung σ = σ0, exp(-E/2kT).
    Notizen: Prepolyurethanes were obtained by reacting the hydroxyl functionality of castor oil with diisocyanates, namely toluene-2,4-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and 4,4′-diphenylmethane diisocyanate, respectively. Homogeneous mixtures of prepolyurethanes and epoxy resin (prepared from bisphenol F in alkaline medium) were prepared in acetone containing 1,3-propanediamine as curring agent. Glass reinforced laminates were prepared by interacting PU/epoxy resin mixtures on glass cloth through compression moulding. The laminates were characterized by chemical resistance to solvents, flexural strength, izod impact strength, and Rockwell hardness. The variation of electrical conductivity σ with temperature was found to confirm with the empirical relation σ = σ0 exp(-E/2kT).
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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  • 111
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Durch Menschutkin-Reaktion wurden Polyurethane mit kationischen Viologen-gruppen hergestellt. Die photochromen Eigenschaften dieser Polymeren in einer Poly(vinylalkohol)-Matrix wurden mit UV- und Laserlicht untersucht.
    Notizen: The Photochromic properties by UV and laser irradiation of cationic polyurethanes with viologen groups introducted by Menschutkin reaction were studied and poly(vinylalcohol) was used as matrix.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 112
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 87-99 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Im Rahmen dieser Arbeit wurden drei verschiedene Meßmethoden für die Bestim-mung der Kristallinität von Polyethylen angewandt. HDPE, LLDPE und LDPE-Pro-ben wurden  -  nach verschiedener Vorbehandlung  -  durch Dichtebestimmung, DSC und Raman-Spektroskopie untersucht. Die mit verschiedenen Methoden gewonnenen Resultate wurden verglichen, und Korrelationen wurden bestimmt.
    Notizen: In this work three different techniques were used to determine the crystallinity of polyethylene. After different pretreatment HDPE, LLDPE, and LPDE samples were investigated by density measurements, differential scanning calorimetry, and Raman spectroscopy. The results were compared and relationships were estabilished between the values measured by the different methods.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 113
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 135-142 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Poly(N-vinylpyrrolidon-co-vinylamin) wurde mit Estern verschiedener Phosphorsäuren (Dimethylphosphit, Methanphosphonsäuredimethylester, Trimethylphosphat und Bis-(2-chlorethyl)-phosphonat methyliert, um physiologisch aktive Polymere zu erhalten. Die alkylierten Produkte wurden mittels IR- und NMR-Spektroskopie sowie Elementaranalyse charakterisiert. Der Alkylierungsumsatz hängt vom verwendeten Alkylierungsmittel ab. Die methylierten phosphorhaltigen Polymeren weisen Herbizidaktivität auf und könnten als Pflanzenwachstumshemmer verwendet werden.
    Notizen: Alkylation of amino groups bounded to a polymer chain with esters of phosphorous acids was studied in order to obtain physiologically active polymers. Poly(N-vinyl-pyrrolidone-co-vinylamine) was chosen as a polymer-carrier. The phosphorous acid esters used were dimethyl hydrogen phosphonate, dimethyl methanephosphonate, trimethyl phosphate and bis-(2-chloroethyl)-hydrogen phosphonate. The composition and structure of the isolated final products was proved by IR- and NMR-spectroscopy and elemental analysis. It is established that alkylation takes place to various extents.The obtained alkylated phosphorous-containing polymers exhibit herbicidal activity and could find application as plant growth retardants.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
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  • 114
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 153-167 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Um die Weichmacherpermanenz in PVC zu verbessern, wurde Decylmethacrylat (DMA) in Gegenwart eines Bleistabilisators (LS) mittels radikalischer Polymerisation auf PVC gepfropft. Die Molekulargewichte und Glastemperaturen der erhaltenen Produkte bestätigten, daß homogene PVC-g-PDMA-Copolymere entstanden waren.
    Notizen: In order to improve the permanence of the plasticizer in a poly(vinylchloride) (PVC) compound we have studied the free radical polymerization and grafting of decyl methacrylate (DMA) onto PVC in the presence of a lead stabilizer. The influence of different parameters has been investigated and homogeneous PVC-g-PDMA copolymers have been obtained. Their molecular weights and the glass transition temperatures were consistent with the grafted nature of the copolymers.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 115
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: The crosslinking behaviour of addition-crosslinking Wacker SilGel 600 silicone was investigated in the temperature range of 50 to 90°C with respect to its dependence on heating time. Measurements of the swelling of thin polymer films on special paper (Pecozet Z10) allow the observation of the swelling process which reaches the swelling equilibrium within a few minutes, the selection of a suitable swelling agent, and the rapid determination of the temperature dependence of the degree of swelling Q. Aside from Q, the „solubility parameter“ of the polymer network, the rate constants, and the activation energy of the crosslinking process can be obtained. Measurements of the swelling combined with determination of Huggins' interaction parameter additionally provide the possibility of determining the density of crosslinking of the polymer films.On the basis of these investigations, a rapid method for characterizing the sheathing of optical fibres could be developed. The cylindrical polymer films detach from the glass core during swelling in toluene (25°C). After 5 min the degree of swelling of the sheathing can be measured.
    Notizen: Das Vernetzungsverhalten des additionsvernetzenden Silicons Wacker SilGel 600 wurde im Bereich von 50 bis 90°C in Abhängigkeit von der Heizzeit untersucht. Quellungsmessungen an dünnen Polymerfilmen auf Spezialpapier (Pecozet Z10) gestatten eine Verfolgung des in wenigen Minuten bis zum Quellungsgleichgewicht ablaufenden Quellprozesses, die Auswahl eines geeigneten Quellmittels und die schnelle Ermittlung der Temperaturabhängigkeit des Quellungsgrades Q. Neben Q sind der „Löslichkeitsparameter“ des Polymernetzwerkes, die Geschwindigkeitskonstanten und die Aktivierungsenergie des Vernetzungsprozesses zugänglich. Bei der Kombination der Quellungsmessungen mit einer Bestimmung des Hugginsschen Wechselwirkungsparameters kann auch die Vernetzungsdichte der Polymerfilme ermittelt werden.Auf der Basis dieser Untersuchungen konnte eine schnelle Methode zur Charakterisierung der Ummantelung von Lichtleitfasern entwickelt werden. Die zylindrischen Polymerfilme lösen sich während der Quellung in Toluol(25°C) vom Glaskern. Nach 5 min kann der Quellungsgrad der Ummantelung bestimmt werden.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 116
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 207-224 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die Synthese und die thermischen Eigenschaften von zwei reaktiven, symmetrischen Azomonomeren und Modellverbindungen wurden untersucht, um thermolabile Mikrokapseln mit thermosensitiven Azogruppen herzustellen. Die Zerfallskinetik dieser thermisch und photochemisch instabilen Verbindungen ist von erster Ordnung, vergleichbar mit AIBN.Durch Grenzflächenpolykondensation der Azomonomeren mit Ethylendiamin, 1,6-Hexamethylendiamin oder Diethylentriamin wurden azogruppenhaltige Polyamide und Polyharnstoffe erhalten, aus denen thermosensitive Mikrokapseln hergestellt wurden. Mit optimierten Herstellungsbedingungen wurden in hohen Ausbeuten Mikrokapseln einheitlicher Größe mit guten Thermo-Transfer-Druckeigenschaften erhalten.
    Notizen: In view of applying thermolabile microcapsules with azo groups as thermosensitive sites it was necessary to study the preparation and the thermal behaviour of two reactive, symmetrical azo monomer-compounds and model compounds. They are thermally and photochemically instable and the kinetics of their decomposition is of first order, comparable to that of AIBN.Azo group-containing polyamides and polyureas were prepared by interfacial polycondensation reaction from ethylendiamine, 1,6-hexamethylenediamine, diethylenetriamine and azo monomer-compounds.These polymers were used to prepare thermosensitive microcapsules. Favourable conditions were found to obtain microcapsules of uniform size, in a high yield, and with good properties in thermo-transfer-print.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 117
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 188 (1991), S. 27-40 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die Fluorierung von Polyethylen und Polyvinylalkohol wurde mit Dichlordifluormethan CCl2F2 (Freon 12) unter Verwendung von Cobalt-60 γ-Strahlung bzw. elektrischer Lichtbogenentladung durchgeführt und der Einfluß von Reaktionstemperatur und -zeit, Katalysator, Verdünnung etc. untersucht. Dabei wurde bei Polyethylen sowohl die Fluorierung als auch die gleichzeitige Chlorierung beobachtet, wobei der Anteil an Fluorierung bei elektrischer Lichtbogenentladung gewöhnlich höher war als bei Verwendung von γ-Strahlung; in beiden Fällen war dennoch die Chlorierung deutlich bevorzugt. Bei Polyvinylalkohol konnten noch höhere Fluorierungs-bzw. Chlorierungsgrade ermittelt werden.
    Notizen: Fluorination of polyethylene and polyvinyl alcohol was carried out by dichloro-difluoromethane under cobalt-60 gamma radiation and under electric spark discharge. The effect of temperature, reaction time, catalyst, inert diluent etc. was studied. Simultaneous chlorination of the polymer samples was observed along with fluorination. The extent of fluorination under electric spark discharge is usually higher than that under gamma radiation. Again, the extent of chlorination is higher than that of fluorination in both the cases. The extent of fluorination as well as chlorination is the highest in case of polyvinyl alcohol.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 118
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Celluloseacetatphthalat (CAP) mit einem Acetylgehalt von 19,5 Gew.-% und einem Phthalylgehalt von 21,4 Gew.-% wurde hergestellt und durch fraktionierte Fällung in fünf Fraktionen mit gleichmäßig abnehmendem Molekulargewicht aufgetrennt. Die Werte für das zahlenmittlere Molekulargewicht (M̄n) dieser Fraktionen wurden membranosmometrisch in 0,05 N NaHCO3 gemessen; die Werte für die Grenzviskosität ([η]) wurden ebenfalls von allen fünf Fraktionen bei verschiedenen Temperaturen bestimmt. Die Beziehung zwischen [η] und M̄n wurde nach der Mark-Houwink-Kuhn-Sakurada-Gleichung ausgewertet, und aus den dabei erhaltenen Werten für v zeigte sich, daß CAP offensichtlich ein sehr steifes Polymeres ist. Die Temperaturabhängigkeit der Viskosität verdünnter CAP-Lösungen wurde nach der Methode von Moore durch einen Arrhenius-Ausdruck beschrieben. Die Aktivierungsenergie der Durchflußgeschwindigkeit hängt sowohl von der Konzentration als auch vom Molekulargewicht ab; aus dem dabei erhaltenen empirischen Parameter Ke kann ebenfalls auf ein steifes Polymeres geschlossen werden.
    Notizen: Cellulose acetate phthalate (CAP) having an acetyl content of 19.5 wt.-% and a phthalyl content of 21.4 wt.-% was prepared and fractionated into five fractions of regularly decreasing molecular weight. The values of the number average molecular weight (M̄n) of these fractions were measured in 0.05 N NaHCO3 by the help of high-speed membrane osmometer. The intrinsic viscosity [η] values for all the fractions of CAP in 0.05 N NaHCO3 were also determined at different temperatures. The Mark-Houwink-Kuhn-Sakurada equation was applied to the obtained results and the [η]-M̄n relationships for CAP have been established. The results of the values of v suggest that CAP is a stiff polymer. The temperature dependence of the viscosity of dilute CAP solutions has been described by an Arrhenius expression according to Moore's treatment. The activation energy of flow was found to depend on both concentration and molecular weight through an empirical parameter (Ke). The Ke value obtained for CAP also indicates that CAP is a rigid polymer.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 119
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 188 (1991), S. 63-72 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Methylhydro-dimethylsiloxancopolymere wurden aus den Hydrolysaten von Dichlordimethylsilan mit 10, 20, 30, 50 und 70 Vol.-% Dichlormethylsilan hergestellt. Die Copolymeren wurden IR-, 1H-NMR-spectroskopisch und chemisch charakterisiert und als Härter für ein funktionalisiertes RTV-Siliconmaterial eingesetzt. Die Vulkanisateigenschaften wurden geprüft; die Copolymeren mit hohem Hydridgehalt verbesserten die mechanischen Eigenschaften und die thermische Stabilität der Vulkanisate.
    Notizen: Synthesis of hydride terminated methylhydro-dimethylsiloxane copolymers from the hydrolyzates of 10, 20, 30, 50 and 70% vol.-% dichloromethylsilane with dichlorodimethylsilane have been carried out. The copolymers were characterized by IR-and 1H-NMR-spectroscopy and standard chemical analysis. They were used as curatives for a standard vinyl functional room temperature vulcanizing (RTV) silicone material based on addition cure, and the vulcanizate properties have been evaluated. The copolymers with high hydride content gave better mechanical properties and thermal stability to the vulcanizates.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 120
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 188 (1991), S. 73-84 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die thermischen Eigenschaften von Polystyrol and Poly(methylmethacrylat) mit verkapseltem und dispergiertem TiO2 wurden verglichen. Die verkapselnden Polymeren zeigen zwei thermische Relaxationsbereiche, deren nach Wunderlich ermittelte Aktivierungsenergien denen von dynamischen Dispersionen ähnlich sind. Es wird vorgeschlagen, daß die Niedertemperaturrelaxation durch lokale Änderungen der Konformation der Makromoleküle hervorgerufen wird, während die Hochtemperaturrelaxation dem normalen Glasübergang einschließlich der Wechselwirkung mit TiO2 vergleichbar ist. Das thermische Verhalten nahe der Zersetzungstemperatur in verschiedenen Atmosphären deutet darauf hin, daß in den verkapselnden Polymeren spezifische Strukturen vorhanden sind, die eine große Menge Sauerstoff adsorbieren können.
    Notizen: Comparing the thermal properties of TiO2 encapsulating polystyrene and poly(methyl methacrylate) with those of TiO2 dispersion polymers it was found that the encapsulating polymers have two thermal relaxation regions. The activation energy of those thermal relaxation regions was determined using the Wunderlich method and it was found that the values are similar to the activation energy for the dynamic dispersion. It is suggested that the low-temperature thermal relaxation is caused by the local change of conformation of molecular chains, while the high-temperature thermal relaxation is similar to that of the normal glass transition temperature including the interaction with TiO2. In addition, the thermal behaviour near the degradation point in different atmospheres indicates that the encapsulating polymer has a specific structure for adsorbing a large amount of oxygen.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 121
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 188 (1991), S. 105-111 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Poly(3-dodecylthiophen) (PDDT) wurde auf chemischem Weg synthetisiert und 1H-NMR-, IR- und UV-spektroskopisch charakterisiert. Das bei Raumtemperatur aufgenommene ESR-Spektrum von PDDT zeigt einen g-Wert von 2.0091 und eine Linienbreite von 6.60 Gauss. Aus der Lösung gegossene und mit Iod dotierte PDDT-Filme hatten eine elektrische Leitfähigkeit von 12 S/cm.
    Notizen: The chemical synthesis of poly(3-dodecylthiophene) is reported. The polymer was characterized by 1H-NMR, IR and UV absorption spectroscopic techniques. The room temperature electron spin resonance spectrum yielded a g value of 2.0091 and a linewidth of 6.60 Gauss. The solution cast polymer films after doping with iodine exhibited an electrical conductivity of 12 S/cm.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 122
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 188 (1991), S. 85-96 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Zwei Methoden zur Herstellung hochmolekularer poröser “Bromamine” (—SO2NBr-Na+) mit Poly (styrol-co-divinylbenzol)-Matrix wurden untersucht, und zwar (a) die Einwirkung von Hypobromiten auf das die entsprechenden Sulfonamidseitengruppen enthaltende Copolymere, und (b) die Einwirkung von Bromiden auf das entsprechende hochmolekulare “Chloramin”. In beiden Fällen wurden Metallsalze des hochmolekularen “Bromamins” erhalten. Das Natriumsalz wurde mit einer 100-proz. Ausbeute an funktionellen Gruppen erhalten; es enthielt 2.1 mmol · g-1 —SO2NBr-Na+ Gruppen, d. h. 4.2 meq · g-1 aktives Brom. Es wurde auch die Stabilität des Harzes getestet, und zwar im Bereich von 20-100°C sowohl im trockenen Zustand als auch in wäßrigen Medien. Darüber hinaus wurden thermoanalytische Messungen bis 1000°C durchgeführt. Es wurden auch Beispiele für die Anwendung des“Bromamins” als polymeres Reagenz für Bromierungen (Iodierungen), Oxidationen, Wasserdesinfektion und Kationenaustausch gegeben. Dieses sehr reaktive polymere Reagenz kann ohne merklichen Verlust seiner Eigenschaften wiederholt debromiert und bromiert werden.
    Notizen: Macromolecular pendant group N-monobromosulphonamide metal salts —SO2NBr-M+ having a macroporous styrene-divinylbenzene matrix structure have been obtained by two methods:(a) by the action of aqueous metal hypobromites on the appropriate macromolecular pendant group sulphonamide, and(b) by the action of an aqueous metal bromide on the appropriate macromolecular N-chlorosulphonamide metal salt.In each case the sodium salt product was obtained with a 100% functional yield and it contained 2.1 mmol.g-1 —SO2NBr-Na+ groups, i. e., 4.2 meq · g-1 of active bromine. The stability of the resin was investigated in the range 20-100°C in the dry state as well as in aqueous media.A thermoanalysis (TG, DTG, and DTA curves) was carried out up to 1000°C and its course was interpreted. The resin has brominating, oxidative, microbiocidic, and ionexchanging properties. It reacts in a reversible way: after the loss of the active bromine, it can be reactivated again.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 123
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 511-518 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ability of tracts of synthetic oligopurine · oligopyrimidines containing both adenosine and guanosine residues to approach the conformation of analogous polypurine · polypyrimidines has been examined as a function of tract length by CD spectroscopy. Tracts of up to 19 contiguous, alternating dA and dG residues yield CD spectra that are distinctly different from that of the analogous alternating polymer. Thus the structural changes reflected in the unusual CD spectrum of poly[d(AG)] · poly [d(CT)] must require even longer tract lengths. Tracts of contiguous adenosines flanked by guanosine residues were seen to approach the CD spectrum of poly[dA] · poly[dT] quite slowly as a function of tract length, requiring more than 24 contiguous adenosines to give CD spectra similar to the homopolymer. These results lead us to the conclusion that oligopurine tracts in vivo are not well modeled by synthetic polypurine · polypyrimidines with one or two base pair repeating units.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 124
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 537-545 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oligomers of (-)-epicatechin with 4β → 8 interflavan bonds, and as many as five monomer units, have been studied by conformational analysis and time-resolved fluorescence. The conformational analysis yields 2x-1 conformations for each oligomer with x monomer units. There are two conformations accessible at each interflavan bond. These conformations are denoted by + and -. The dominant conformations for the trimer and higher oligomers have an interaction between the phenolic hydroxyl groups on monomers i and i+2. This interaction involves the hydroxyl group at C(5) on monomer i, and either C(13) or C(8) of monomer i+2, depending on whether the conformation of the two intervening interflavan bonds is + + or + -, respectively. Minor contributions to the ensemble for the tetramer and pentamer are made by conformations that contain the sequence of successive interflavan bonds denoted by -+ or --. In -+ the interaction between monomer units i and i + 2 involves an aliphatic hydroxyl with a phenolic hydroxyl, and there are no hydroxyl-hydroxyl interactions between units iand i + 2 in --. The onset of a different decay law for the fluorescence when x increases from 3 to 4 may be associated with the appearance of the -+ and -- conformations as minor constituents in the ensemble.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 125
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: C-terminal analogues of neuropeptide Y (NPY) of small molecular size have been synthesized. The influence of chain length, single or multiple amino acid substitution, and segment substitutions on receptor binding, pre- and postsynaptic biological activity, and conformational properties have been investigated. Receptor binding and in vivo assays revealed biological activity for NPY Ac-25-36 that increased with increasing α-helicity. In attempts to stabilize the α-helical content, three independent types of modified NPY Ac-25-36 analogues were synthesized. Strong agonistic activities could be detected in a series of discontinuous analogues, which are constructs of N-terminal parts linked via different spacer molecules to C-terminal segments. One of the most active molecules was NPY 1-4-Aca-25-36 (Aca, ε-aminocaproic acid). For the first time conformational properties of a series of small NPY analogues have been investigated by CD, and correlated with biological activity and receptor binding. A C-terminal dodecapeptide segment of NPY with an amount of 50% substitution to the native C-terminal sequence of NPY was found to exhibit significant receptor binding.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 126
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 663-670 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The possibility of using molecular dynamics techniques as a tool for simulated annealing is tested in the case of the molecule of biological interest N-acetyl, N′-methyl amides of 3(S)-hydroxy, 4(S)-amino 6-methyl heptanoic acid [(3S, 4S)-statine] and of its (3R,4S) diastereomer. The approach is able to reach global minimum in the conformational space in the case of the mentioned molecule. A description of the method is given. The use of fractional fluctuations of the internal potential energy as an indicator able to point out transition from a given minimum region to a deeper one is investigated. The results about the lowest energy conformation of (3S,4S) diastereomer are in fairly good accordance with the results obtained in the case of search within the whole Conformational hyperspace.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 127
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Automated assignment of proteins is greatly simplified using data from 3D-nmr spectra. A strategy is presented which makes use of 3D-TOCSY-TOCSY and 3D-TOCSY-NOESY; its potential is demonstrated with the example of the spectra of BPTI.The discussion of the potential of 3D-nmr includes the introduction of a simple graph for the description of the information content of multidimensional nmr spectra.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 128
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 725-733 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1,4-Piperazine and 4-hydroxy proline, two small cyclic polyfunctional systems with defined stereochemistry, were introduced as “molecular scaffolds.” We define a “bioactive topology,” which is a derived putative low-energy conformation obtained through theoretical conformational analysis of substance P. Substitution of these molecular scaffolds by pharmacophors characteristic of the bioactive topology of the C-terminal hexapeptide of substance P resulted in active, partially nonpeptidal substance P mimetic agonists. The study discusses the concepts arid tools used to achieve this structural transformation, and points out the need to address flexibility-rigidity issues in an attempt to maintain sufficient molecular plasticity.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 129
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 803-811 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 21-peptide amide antibiotic gallidermin is a potential therapeutic against acne disease. It belongs to the class of polycyclic lanthionine and α,β-clidehydroamino acids containing polypeptides, which were named “lantibiotics.” The structural gene of the recently elucidated lantibiotic gallidermin encodes a precursor peptide containing Ser, Thr, and Cys residues in the Oterminal prolantibiotic part, and an unusually hydrophilic leader peptide. The ribosomally synthesized pregallidermin is posttranslationally modified and processed to a complex peptide antibiotic with four/sulfide rings and two unsaturated residues.The complete solution structure of gallidermin was determined in triffuoroethanol : water (95 : 5) and dimethylsulfoxide by two-dimensional 1H-nmr at 500 MHz, using a combination of double quantum filtered correlated spectroscopy, homonuclear Hartman-Hahn, and nuclear Overhauser enhancement spectroscopy experiments. Using a total number of 152 distance constraints from NOEs and 14 torsional constraints, derived from coupling constants, we obtained a screwlike solution structure of gallidermin. Restrained molecular dynamics simulations yielded a set of five converging structures with an atomic rms difference of 1.7 Å for the backbone atoms, not dependent on the starting structure. The spatial structure model is in excellent agreement with the amphiphilic and channel-forming properties of gallidermin on membranes and its tryptic cleavage at the exposed site between residues 13 and 14.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 130
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We have solved the crystal structures of nine pseudo-peptide analogues deriving from the hydrazino analogue of glycine or valine (NβH2-NαH-CαHR-CO2H, R = H or iPr) or proline (NβH2-Nα-CαH-CO2H) and containing the hydrazide (CO-NβH-Nα) or Nβ-Z-aminoamide peptidomimetic link. This study gives access to the average geometry of these two links, to their inter- and intramolecular interaction modes, and to their influence on the conformational properties of the molecules.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 131
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1471-1481 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: DNA is generally found within viruses and cells in a tightly packaged state, typically occupying only 10-4-10-6 of the volume of the uncondensed DNA wormlike coil. Condensation can be induced in vitro at low salt by the naturally occurring polyamines spermidine3+ and spermine4+, by hexammine cobalt (III), and even by Mg2+ in methanol-water mixtures. These condensates generally have an orderly, toroidal, or rodlike shape and size similar to that of DNA gently lysed from phage heads. It is also striking that the condensate size distribution is independent of DNA molecular length from 400 to 40,000 base pairs (bp), but that shorter DNA molecules (e.g., 150-bp mononucleosomal DNA) cannot condense in this fashion. We have constructed a successive association equilibrium theory to attempt to explain these results, using an equation devised by Tanford for micelle formation. Most of the obvious attractive and repulsive free energy contributions (mixing, bending, hydration, and other nearest-neighbor interactions) are linear in the amount of DNA incorporated, but the net attractive ΔG° grows nonlinearly because of the increasing average number of nearest neighbors of each duplex as the particle grows. In order that the size distribution have a maximum, a quadratic repulsive free energy is also required, arising from the electrostatic self-energy of the incompletely neutralized particles. The net attractive free energy per base pair interaction is tiny, on the order of 10-3 kT. Despite the apparent generally correct order of magnitude of the various free energy terms, the calculated size distribution is smaller and narrower than observed experimentally. It appears that the size distribution of condensed particles is determined kinetically rather than thermodynamically. Very short DNA molecules cannot nucleate stable aggregates because they cannot develop adequate overlap, either internally or intermolecularly. A substantial fraction of rodlike condensates is observed in aqueous solutions only with a rather inefficient condensing agent, permethylated spermidine. This suggests that slow condensation kinetics may be required to overcome the high activation energy of highly distorted DNA bends or kinks at the turning points of rods. Evidence is reviewed that condensation may be associated with localized helix structure distortion provoked by condensing agents.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 132
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1503-1512 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of cyclic retro-inverso dipeptides - 2-[(4-hydroxy)benzyl]-5-benzyl-4,6(1H,2H,3H,5H)-pyrimidinedione (c[mPhe-gTyr]), 2-benzyl-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione (c[mTyr-gPhe]), and 2-benzyl-5-amino-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione {c[(α-amino)mTyr-gPhe]} - were synthesized in order to define the minimum structural requirements for binding affinity with opiate receptors and biological activity. Although the first two compounds lack a free amine proposed to be necessary for receptor recognition, the c[mPhe-gTyr] and c[mTyr-gPhe] analogues serve as model molecules in conformational studies of the target analogue, c[(α-amino)mTyr-gPhe]. The cis- and trans-c[(α-amino)mTyr-gPhe] contain all the functional groups such as the amine and phenolic groups in the tyrosine, and the aromatic group in the phenylalanine, necessary for opiate activity. In addition, the c[(α-amino)mTyr-gPhe] analogues possess similar geometries to the Tyr-Pro part of morphiceptin (Tyr-Pro-Phe-Pro-NH2) whose high μ-receptor activity is attributed to conformations with the Tyr-Pro amide bond in a cis conformation because the peptide bonds assume a cis conformation. However, both analogues are inactive in the guinea pig ileum and the mouse vas deferens assays. This may result from wrong orientation of the benzyl group of the gPhe residue with respect to the (α-amino)mTyr residue.Conformational studies of these molecules using 1H-nmr spectroscopy and molecular mechanics calculations will be reported in the following paper. Results of conformational analysis should provide information about backbone-side-chain interactions in the retro-inverso peptide chains since all the fundamental structural elements of the retro-inverso peptides are included in these model systems even though the peptide bonds must assume a cis conformation.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 133
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new model structure is proposed for the silk I form of the crystalline domains of Bombyx mori silk fibroin and the corresponding crystal form of poly(L-Ala-Gly). It was deduced from conformational energy computations on stacked sheet structures of poly(L-Ala-Gly). The novel sheet structure contains interstrand hydrogen bonds but is composed of antiparallel polypeptide chains whose conformation differs from that of the antiparallel β-sheets that constitute the silk II structure. The strands of the new sheet have a two-residue repeat, in which the Ala residues adopt a right-handed and the Gly residues a left-handed sheet-like conformation. The computed unit cell is orthorhombic, with cell dimensions a = 8.94 Å, b = 6.46 Å, and c = 11.26 Å. The model accounts for most spacings in the observed fiber x-ray diffraction patterns of silk I and of the silk-I-like form of poly(L-Ala-Gly), and it is consistent with nmr and ir spectroscopic data. As a test of the computations, the well-established β-sheet structure of silk II and the corresponding form of poly(L-Ala-Gly) have been reproduced. The computed energies for the two forms of poly(L-Ala-Gly) indicate that the silk-II-like form is more stable, by about 1.0 kcal/mol per residue. The main difference between the two structures is the orientation of the Ala side chains of neighboring strands in each sheet. In the Pauling-Corey β-sheet and in the silk II form, referred to as an “in-register” structure, the Ala side chains of every strand point to the same side of a sheet. In the silk I structure, referred to as “out-of-register,” the side chains of Ala residues in adjacent strands point to opposite sides of the sheet.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 134
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational dynamics of α- (1 → 4)- and α- (1 → 6)-glucan homooligomers in the nanosecond time domain have been compared by measuring the 13C-nmr longitudinal relaxation times T1 for carbons of the terminal and interior sugar residues. Measurements are reported on monomeric glucose and on oligomers containing up to ten glucose residues at room temperature in aqueous solution at concentrations of 3 and 20 g/dL. The carbons of terminal residues display longer relaxation times than do those of interior residues, presumably as a consequence of a greater degree of conformational mobility of the chain ends. The T1s of the reducing terminal residues of all oligomers are significantly longer than those of the corresponding nonreducing termini, a phenomenon that we associate tentatively with the anomeric equilibrium at the reducing end. Carbons of the reducing terminal residues in the β-anomeric form relax more slowly than their α-anomeric counterparts. At 20 g/dL the mean T1s for carbons of the terminal and interior residues attain asymptotic behavior with increasing chain length at a chain length of about six residues, and carbons of the α- (1 → 4)-linked maltooligomers relax significantly more slowly than those of the corresponding α-(1 → 6)-linked isomaltooligomers. The T1s of both glucan series increase with decreasing concentration. This concentration dependence disappears below 3 g/dL, where the T1s of the two series of homoligomers are no longer distinguishable. This suggests that in dilute aqueous solution at room temperature viscous damping effects predominate over contributions to the T1-sensitive conformational dynamics from structural differences in the glycosidic linkage region. At 3 g/dL the approach to long chain-length asymptotic behavior is more protracted than at 20 g/dL, and the T1s of carbons of interior oligomeric residues appear to match the corresponding high-polymer behavior at a chain length of eight and greater.
    Zusätzliches Material: 5 Ill.
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  • 135
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 136
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We describe statistical mechanical theory that aims to predict protein stabilities as a function of temperature, pH, and salt concentration, from the physical properties of the constituent amino acids: (1) the number of nonpolar groups, (2) the chain length, (3) the temperature-dependent free energy of transfer, (4) the pKa's (including those in the native state) and their temperature dependencies. We calculate here the phase diagrams for apomyoglobin and hypothetical variant proteins. The theory captures essential features of protein stability including myoglobin's Tm vs pH as measured by P. L. Privalov [(1979) Advances in Protein Chemistry, Vol. 33, pp. 167-241] and its ionic strength vs pH phase diagram as measured by Y. Goto and A. L. Fink [(1990) Journal of Molecular Biology, Vol. 214, pp. 803-805].The main predictions here are the following: (1) There are three stable states, corresponding to native (N), compact denatured (C), and highly unfolded (U), with transitions between them. (2) In agreement with experiments, the compact denatured state is predicted to have enthalpy closer to U than N because even though there is considerable hydrophobic “clustering” in C, this nevertheless represents a major loss of hydrophobic contacts relative to configurations (N) that have a hydrophobic “core.” (3) C becomes more prominent in the phase diagram with increasing nonpolar content or decreasing chain length, perhaps thus accounting for (a) why lysozyme and α-lactalbumin differ in their denatured states, and (b) why shortened Staph nuclease molecules are compact. (4) Of major importance for protein calorimetry is Privalov's observation that the enthalpy of folding, ΔH (T, pH) is independent of pH. The theory accounts for this through the prediction that the main electrostatic contribution to stability is not enthalpic; the main contribution is the entropy, mainly due to the different distributions of protons and small ions in the native and denatured states.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 137
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1709-1720 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A systematic theoretical study of the CD of double-stranded poly (dG-dC) and its complexes with small molecules is presented. The intrinsic CD of the polymer and the induced CD of a transition belonging to a molecule bound to DNA are calculated using the matrix method. The calculations show considerable differences between pyrimidine-purine and purine-pyrimidine binding sites, and we find that the induced CD of a groove bound molecule is one order of magnitude stronger than that of an intercalated molecule. The results form a sound basis for interpreting the CD of ligand-DNA systems in terms of molecular geometry, interactions, and spectroscopy.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 138
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1737-1746 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular dynamics simulations without explicit inclusion of solvent molecules have been performed to study the motions of Lewisa and Lewisb blood group oligosaccharides, and two blood group A tetrasaccharides having type I and type II core chains. The blood group H trisaccharide has also been studied and compared with the blood group A type II core chain. The potential energy surface developed by Rasmussen and co-workers was used with the molecular mechanics code CHARMM. The lowest energy minima of the component disaccharide fragments were obtained from conformational energy mapping. The lowest energy minima of these disaccharide fragments were used to build the tri- and tetrasaccharides that were further minimized before the actual heating/equilibration and dynamics simulations. The trajectories of the disaccharide fragments, e.g., Fuc α-(1 → 4) GlcNAc, Gal β-(1 → 4) GlcNAc, etc., show transitions among various minima. However, the oligosaccharides were found to be dynamically stable and no transitions to other minimum energy conformations were observed in the time series of the glycosidic dihedral angles even during trajectories as long as 300 ps. The stable conformations of the glycosidic linkages in the oligosaccharides are not necessarily the same as the minimum energy conformation of the corresponding isolated disaccharides. The average fluctuations of the glycosidic angles in the oligosaccharides were well within the range of ±15°. The results of these trajectory calculations were consistent with the relatively rigid single-conformation models derived for these oligosaccharides from 1H-nmr data.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 139
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 449-458 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The solution conformation of tubulin-β(422-434)-NH2 (YQQYQDATADEQG-NH2) and its Nac-DATADEQG-NH2 fragment has been studied by two-dimensional 1H-nmr spectroscopy in CD3OH/H2O (90/10 v/v) at neutral and low pH. The 13 amino acid peptide is a segment of the C-terminal region of tubulin, and is directly involved in the selective binding site with microtubule-associated proteins MAP-2 and the τ protein. Based on correlated spectroscopy, total correlation spectroscopy, and rotating frame nuclear Over-hauser effect spectroscopy experiments, a complete assignment of all proton resonances was achieved, and the conformation of the backbone could be deduced from coupling constants, NH temperature coefficients, and nuclear Overhauser effects. The spectroscopic evidence indicates that the T8-Q12 section of both molecules forms one complete α-helical turn, stabilized by a NH(Q12)-C=O(T8) hydrogen bond. Furthermore, strong pH-dependent backfolding of the E11 side chain to its own NH proton was found. In addition, close proximity between the aromatic side chains of Y1, Y4, and the α-helical part, resulting in some substantial chemical shift changes when comparing the entire 13-mer with the octamer, could be explained in terms of a nonclassical kink in the DATA section. The conformational space is dominated by extended structures and the nonextended conformers are only a minor, yet spectroscopically clearly discernible entity. The presence of the α-helical region at the C-terminus of the 13-mer is important because binding studies of this peptide with MAP-2 indicate that the D10-E11-Q12-G13 fragment is critical for the binding interaction.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 140
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 529-535 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Absorption and CD spectra of the π-π* transition near 200 nm are calculated for helical (Pro)10 forms I and II with a variable proline ring conformation characterized by torsion angle χ2 in the range -60° to 60°. The spectra for poly (Pro) I are not sufficiently sensitive to χ2 to suggest a preferred ring conformation. The spectra for poly (Pro) II are more sensitive to χ2, and suggest preferred ring conformations near either or both of the χ2regions -50 ± 10° and 50 ± 10°.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 141
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 569-586 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An improved model for calculating the CD of polypeptides has been developed. Excited state wavefunctions were derived from CNDO/S (complete neglect of differential overlap, spectroscopic) calculations on N-methylacetamide. Four discrete peptide-localized transitions were employed: π0π*(NV1), π+π* (NV2), nπ*, and n′π*. Inclusion of the π+π*transition (λ0 = 140 nm) significantly improves the accuracy of the calculated CD spectra in the 180-250-nm region. Spectra were computed for various helical structures, including right-handed α-, αII-, ω-, π-, 310-, and poly(proline)I-helices, and the left-handed poly(proline)II-helix. Sensitivity to changes in the peptide backbone geometry and chain length are examined. Electronic factors such as ground-state charge distribution, hybridization effects, and basis set deorthogonalization have been investigated. The nonconservative nature of the poly (Pro) I and II CD spectra is reproduced, and the helix band present in earlier exciton calculations on the α-helix has been diminished.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 142
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1087-1094 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ultraviolet hyperchromicity experiments indicate that in DNA duplex formation, a C-T mismatch is destabilizing in the center of a duplex, but behaves as a stable base pair at the terminus of a duplex. The C-T base pair is thought to contain two hydrogen bonds, but has thermodynamic parameters (ΔH° and ΔG° of dissociation) that are similar to a G-C base pair. AMBER molecular mechanics calculations were performed to study the possible structural properties of DNA duplexes with central and terminal C-T combinations. These calculations also indicate that a central C-T pair destabilizes a duplex, while terminal C-T forms a stable base pair. Hydrogen bonding between cytosine and thymine occurs only in the energy-minimized structures when the helix diameter decreases and the propeller twist angle between the bases increases. These changes are found to occur only at the end of a duplex in the calculations, which may explain the experimental results.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 143
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1115-1134 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An understanding of helix dynamics can aid in interpreting the motions of proteins. The conformational transitions that occur also appear to play a role in protein folding. Structural studies of isolated peptides in solution are just becoming available. However, detailed analysis of the helix-coil transition is still not available and will be difficult to obtain experimentally. For these reasons, we performed a long molecular dynamics simulation of polyalanine at high temperature. Using this approach, we obtain a description of the overall structure and inherent flexibility of the chain as well as a structural picture of the conformational changes that occur. In this way, we can address both equilibrium properties of the peptide and the dynamics and mechanism of the structural transitions. Our results correlate fairly well with the available experimental data and previous simulations aimed at addressing α-helix dynamics. The peptide spends the bulk of its time fluctuating between different conformations with intermediate helix contents. Transitions between highly ordered and highly disordered structures were rare, but they occurred rapidly. Our distribution of conformations favored collapsed states. Hence, our transitions to structures with high helical content were from fluctuating compact structures. The conversion between helix and coil occurred sequentially on a residue-by-residue basis. However, there was local cooperativity; the transition of a residue to the coil state was facilitated after a neighboring group became non-helical. The relevance of our results to protein folding is also discussed.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 144
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1171-1180 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complex dielectric response of calf thymus DNA in aqueous saline solutions has been measured from 1 MHz to 1 GHz. The results are presented in terms of the relaxation of the incremental contributions to the permittivity and conductivity from the condensed counterions surrounding the DNA molecules. Measurements of the low-frequency conductivity of the samples also lends support to the condensed counterion interpretation.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 145
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Neurotoxic peptides from venoms of scorpions and honey bees exhibit a consensus pattern in the two disulfide bridgings related to the sequence portions Cys-X-Cys and Cys-X-X-X-Cys. A revised three-dimensional structure of charybdotoxin, as determined by two-dimensional nmr spectroscopy, confirms that the consensus cystine dislocation generates in all these toxins a common structural element, i.e., the cystine-stabilized α-helical (CSH) motif, which may be correlated with their common ion channel blocking activity.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 146
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1205-1212 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The structure of valinomycin in a range of organic solvents of varying polarity and in detergent and lipid dispersions has been studied by Fourier transform ir Spectroscopy. In solvents of low polarity such as chloroform, ir spectra of valinomycin are fully consistent with the bracelet structure proposed on the basis of nmr Spectroscopy, showing a single narrow amide I component attributable to the presence of β-turns and a single band arising from nonhydrogen-bonded ester C=O groups. K+ complexation results in a downward shift in the amide I band frequency, indicating an increase in the strength of the amide hydrogen bonds, along with a shift to lower frequencies of the ester C=O absorption due to a reduction in electron density in these bonds upon complexation. Identical results were obtained with NH4+, a finding not previously reported.In solvents of both medium (CHCl3/DMSO 3 : 1) and high (pure DMSO) polarity, we find evidence of significant disruption of the internal hydrogen-bonding network of the peptide and the appearance of a band suggesting the presence of free amide C=O groups. In such solvents, complexation with K+ and NH4+ was not observed.The structure of valinomycin in detergent micelles resembles that in nonpolar organic solvents. However, changes were found in the amide I and ester carbonyl maxima as 2H2O penetrated the micelle which suggest significant interaction between the solvent and peptide. Complexation with K+ was reduced in cationic detergent micelles as a result of a decrease in the effective K+ concentration due to charge repulsion at the micelle surface.In lipid bilayers the structure again appears identical to that found in chloroform. As in detergent micelles, the amide I and ester carbonyl bands exhibit shifts that indicate interactions with solvent. Complexation with both K+ and NH4+ is efficient, producing spectral changes similar to those seen in organic solvents.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 147
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Modified self-consistent phonon theory when applied to the DNA double helix indicates the existence of fairly long-lived states in which single interbase H bonds are disrupted. One can then postulate a number of situations in which particular disrupted H bonds can enhance particular proton exchange. In this paper we postulate a number of such partially open states for a B-conformation GC base pair and calculate the probability of each of these states for a B-conformation poly(dG) · poly(dC). We compare these probabilities to those probabilities needed to explain various observed proton exchange rates. We propose that, for a GC base pair in B conformation, there are two amino proton exchangeable states - a cytosine amino proton exchangeable state and a guanine amino proton exchangeable state; both require the disruption of only the corresponding inter base H bond. The imino proton exchange, however, requires the disruption of all three inter base H bonds and this defines a third open state. Our calculated probabilities for a GC base pair in these three states are in fair agreement with available experimental estimates from measurements of amino and imino proton exchange.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 148
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Individual DNA molecules in the Mb size range were monitored by epifluorescence video microscopy during field inversion gel electrophoresis (FIGE). DNA migrating in an agarose gel gives rise to characteristic V-conformational elements and when doing so exhibits a reduced mobility. When the V-conformational elements per DNA molecule are few, the degree of retardation appears proportional to the number of V's, and since larger DNA species exhibit more V's, to DNA size. For a particular pulse frequency, the proportionality breaks down progressively as the number of V-conformational elements per DNA molecule increases. The loss of proportionality between DNA length and migration rate is being correlated with the macroscopically observed loss of electrophoretic size discrimination known as band compression. For a particular pulsing frequency and size class of DNA, the loss of size discrimination is thought to be due to the different orientations of migration, caused by the asymmetric distribution of V-conformational elements when the number of these elements is moderate. Small and very large DNA by contrast migrate with the direction of the biased field. These events, analyzed by microscopic measurement, are consistent with the known macroscopically observed double-valued mobilities in FIGE.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 149
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 415-425 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: An expanded series of alkoxy-and oligo(oxyethylene)-substituted thermotropic polyesters with flexible decamethylene spacers in the main chain, which have higher molecular weights than those described in an earlier report, were prepared and characterized. All of the polymers in the series are soluble in common organic solvents, and have low melting temperatures (Tm) and isotropization transition temperatures (Ti). The members of the series with oligo(oxyethylene) substituents form both smectic and nematic phases.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 150
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 447-460 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The interactions of the polyelectrolyte carboxymethylcellulose (sodium salt) with salts, dyes and surfactants have been studied by viscometry, conductometry, spectrophotometry and membrane potential measurements. The compact conformation of the polyelectrolyte has been realized in all the environments. The average radius of gyration, s̄, and the intrinsic viscosity, [η], decline with increasing concentration of the additives. This and the narrow pseudoternary single-phase zones for both the carboxymethylcellulose (sodium salt)/CTAB (cetyltrimethylammonium bromide)Systematic name: hexadecyltrimethylamounium bromide. / Triton X-100 (α-alkylphenyl-ω-hydroxypoly(oxyethylene))/water and the carboxymethylcellulose (sodium salt)/CTAB/Tween 20 (poly(oxyethylene)sorbitan monolaurate)/water system suggest instability of the polymer in presence of the additives. The spectral results indicate dye aggregation (stacking) on the flexible polymer chain. The binding of CTAB with the polyelectrolyte is Langmuirian in absence of KCl and strongly co-operative in its presence. Thermodynamic parameters have been evaluated in the light of both Langmuir and Scatchard equations. Considering water and polymer to be in separate phases, the free energy of transfer of CTAB from the aqueous to the polymer phase has been calculated.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 151
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 603-616 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A statistical theory is presented, concerning polyfunctional crosslinking of polymer initially heterogeneous with respect to molecular weight. It is an extension of Flory's theory concerning tetrafunctional crosslinking. Relationships between the equilibrium shear modulus, the crosslinking index, the sol fraction, and the functionality of the crosslinks are given for uniform polymer and for non-uniform polymer of unknown as well as known molecular weight distributions. It appears that at and just beyond the gel point, fractionation of the primary polymer has occurred in such a way that the number- and weight-average molecular weights of the primary polymer molecules, present in the network fraction, are equal to the weight- and z-average molecular weights of the original primary polymer, independent of the functionality of the crosslinks.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 152
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polyesters were prepared from 4,4′-dihydroxybiphenyl and various aryloxyterephthalic acids or various disubstituted terephthalic acids. The aryloxyterephthalic acids were prepared by nucleophilic substitution of dimethyl nitroterephthalate with phenoxide ions. The disubstituted terephthalic acids were synthesized by double alkylation of diethyl 2,5-dihydroxyterephthalate with various alkyl bromides containing aromatic rings in the ω-position. The silyl method was primarily used for the polycondensation procedure. The resulting polyesters were characterized by elemental analyses, viscosity measurements, wide-angle X-ray scattering and differential scanning calorimetry measurements, and by optical microscopy. All polyesters proved to be semicrystalline, meltable materials forming a nematic phase above their melting points. The substituents of terephthalic acid enhance the solubility in organic solvents, so that all polyesters are soluble in CH2Cl2/trifluoroacetic acid mixtures and some of them even in hot N,N-dimethyl-formamide or methyl benzoate.
    Zusätzliches Material: 4 Ill.
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  • 153
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 673-677 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Dextran derivatives containing primary amino functions were prepared by reacting 4-nitrophenyl carbonate-substituted dextran with the mono-protected diamine N-tritylenediamine (7). Acidic treatment of the resulting dextran N-[2-(N-trityl)aminoethyl]carbamate (8) yields dextran N-(2-aminoethyl)carbamate (5a). Alternatively, aminodextran derivatives were prepared by adding 4-nitrophenyl carbonate-substituted dextran to a large excess of a diamine or a triamine.
    Zusätzliches Material: 1 Ill.
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  • 154
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 709-720 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Tracer diffusion coefficients D* of both components were measured in mixtures of polystyrene (PS) and polymethylstyrene (PMS), a random copolymer from 60 wt.-% of m-methylstyrene and 40 wt.-% of p-methylstyrene. The results are interpreted in terms of the free-volume theory which yields master curves even for “asymmetric” mixtures of oligomer and polymer chains, if D* is drawn versus the distance from the glass transition temperature, T-Tg. Whereas D* was measured by the forced Rayleigh scattering technique, we also studied photon correlation spectroscopy in these mixtures and observed “slow modes” with decay constants that correspond to diffusion coefficients 2-3 decades smaller than the interdiffusion coefficient.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 155
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The synthesis of highly amino-sensitive activated carbonates based on tert-butoxycarbonyl(BOC)-modified monomers was performed by reaction of phthalimido chloroformate and phenyl chloroformate with the free OH groups of N-(2-hydroxy-2-methylpropyl)methacrylamide (1), N-(3-hydroxy-3-methylbutyl)methacrylamide (2) and N-(2-hydroxy-2-methylpropyl)-6-methacrylamidohexanamide (6), respectively. The monomeric carbonates were radically homo- and copolymerized with methyl methacrylate (MMA). The kinetics of aminolysis of these polymers with hexanamide was followed by UV and NMR spectroscopy. Differences between phthalimide- and phenyl-containing systems, neighbouring group effects, influence of different comonomers and spacer groups on the reactivity of the activated carbonates are discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 156
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: With calorimetric measurements the kinetics of the free-radical polymerization of various diacrylates in several polymeric binders have been investigated. The reaction was initiated by radicals formed through photolysis of α-isopropoxydeoxybenzoin. In each case, the polymerization rate depends on the conversion degree. Mainly, this fact results from changes in the termination mechanism of the polymerization chain reaction. By means of the light intensity exponent such mechanistical changes can be quantitatively followed. Both, the results obtained by stationary and non-stationary irradiation experiments lead to the same conclusions. The properties of the polymeric binders possess a stronger influence on the kinetics compared with the structural changes of the diacrylates used.
    Zusätzliches Material: 6 Ill.
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  • 157
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 857-861 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The influence of experimental conditions and the nature of the catalytic system on the yield of products insoluble in methanol from the carbonyl-olefin exchange reaction (COER) was investigated. It was established that the COER of some α, β-unsaturated carbonyl compounds can be catalyzed by transition metal halides (WCl6, MoCl5), by oxo compounds (WOCl4), and by binary systems (WCl6 + AlCl3, MoCl5 + AlCl3). Under the influence of these catalysts, some α,β-unsaturated ketones can be transformed into conjugated polymers via different pathways. That is why the yield of the polymer product can be higher than calculated on the basis of the simple COER.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 158
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 863-866 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The processes which take place with the α,β-unsaturated compound 1,2,3,3-tetraphenyl-2-propen-1-one (1) under the influence of WCl6 were investigated. Special attention was paid to the low-molecular-weight products. It was established that beside polydiphenylacetylene and benzophenone also benzil, tetraphenylethylene and molecular oxygen are present in the product mixture. Their formation is explained as a result of a redistribution of the atoms connected with double bonds according to olefin metathesis (OM), carbonyl-olefin exchange reaction (COER) and reductive coupling (RC) of carbonyl compounds, accompanied by molecular oxygen evolution. The yields of products insoluble in methanol are sometimes higher than a simple stoichiometry would allow. This can be attributed to the participation of both the inner double bonds of the polymer and the low-molecular-weight products.
    Materialart: Digitale Medien
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  • 159
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The cationic polymerization of 3,3-bis(azidomethyl)oxetane (BAMO) was compared with the polymerization of 3,3-bis(chloromethyl)oxetane (BCMO). The initiating system, boron trifluoride diethyl etherate/diethylene glycol (system. name: 2,2′-oxydiethanol) was used and it was shown that unusually high concentrations were necessary to observe polymerization. NMR analysis of poly(BAMO), produced by this initiating system, suggested that BAMO polymerization proceeds through the activated-monomer mechanism. The oligomer functionality, which was found close to 2, supports this suggestion. It was also shown that by copolymerization of BAMO with 3-chloromethyl-3-(2,5,8-trioxadecyl)oxetane the crystallization tendancy and the glass transition temperature of poly(BAMO) decreased.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 160
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 945-957 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Upon n → π* (436 nm) excitation of azobenzene probes 1, 2 and 3 in a solid film of poly(methyl methacrylate) we observe cis-trans isomerization and a monoexponential approach towards the photostationary state; upon π → π* (313 nm) irradiation this approach is bi-exponential. The latter is not due to the loss of concentration homogeneity during the reaction. By transferring the concept of dual isomerization mechanisms (rotation and inversion) from former work we reinterpret the “fast” component of isomerization at 313 nm excitation as being due to rigidly held molecules unable to isomerize via the rotation mechanism, but undergoing internal conversion and subsequent inversion, and the “slow” component as being due to molecules isomerizing by rotation. On 436 nm irradiation only one isomerization mechanism is active, viz. inversion.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 161
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 21-34 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In order to improve our comprehension of the crystalline structure of polyamides, two regular odd terpolyamides containing 3-aminopropanoyl, 5-aminopentanoyl and 7-aminoheptanoyl units were prepared by the active ester polycondensation method. The choice of the sequencing order in the starting compounds (called here heterotrimers) and the various routes leading to them are discussed. It was found that both the reactions and the purification of intermediates were most conveniently performed by combining the heterodimer of the lower amino acids with the higher amino acid. The polycondensation was carried out through a multiple step process either in solution or in the solid-state at a temperature below 200°C. 13C NMR spectra showed that no rearrangement during the polycondensation occurs under these conditions. The terpolyamides have sufficiently high molecular weights to provide good films for crystallographic studies. The two terpolyamides of inversed order do not cocrystallize even when coprecipitated from a solution, probably because of their different crystalline structures.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 162
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 75-83 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Partially acetylated cellulose was synthesized by homogeneous acidic and basic saponification of cellulose triacetate (fully acetylated cellulose) and by homogeneous acetylation of cellulose dissolved in molten N-ethyl-pyridinium chloride. The result of 1H NMR spectroscopic investigations was that acetylation and acid saponification lead to products with different esterification of the hydroxy groups at C2, C3 and C6 whilst basic saponification leads to uniform acetylation. Furthermore, the solubility of the cellulose acetates depends on the method of preparation.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 163
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polymers with chiral asymmetric crown ether units (5, 6, 7 and 8) were synthesized via cationic cyclopolymerization of methyl 2,3-bis{O-[2-(2-vinyloxyethoxy)ethyl]}-4,6-O-benzylidene α-D-altro-, α-D-galacto-, α-D-gluco- and α-D-manhopyranosides (1, 2, 3 and 4), respectively. The enantioselective transport of the methyl ester of phenylglycine (PhGlyOCH3) and phenylalanine (PhAlaOCH3) was examined through a bulk chloroform solution of chiral polymers from one aqueous solution to another. The transport rate of PhAlaOCH3 was larger than that of PhGlyOCH3 for every host polymer. For polymer 7, the optical purity of PhAlaOCH3 transported from one to the other phase was 12,6%, and the ratio of rate constants for the faster moving enantiomer A and the slower moving enantiomer B (kA*/kB*) was 1,48. The faster moving enantiomer was the L-isomer except for the systems polymer 7 - PhAlaOCH3 and polymer 8 - PhAlaOCH3. This enantioselectivity is caused by the diastereotopic faces of the crown ether units in the host polymers.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 164
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1649-1654 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The emission characteristics of the excited state of tris(2,2′-bipyridine)ruthenium(II), Ru(bpy)32+, adsorbed on a silk fibroin membrane is studied. The life time of the excited state of the adsorbed Ru(bpy)32+ is unusually longer (1 000 ns) than that of Ru(bpy)32+ in aqueous solution (598 ns). The excited state of the adsorbed Ru(bpy)32+ is quenched by oxygen when dipped in methanol, but not in water. The quenching by oxygen in methanol follows the Stern-Volmer equation. The luminescent characteristics of the adsorbed Ru complex is discussed in terms of binding in hydrophobic domains composed of tyrosine residues of the protein.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 165
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The cationic copolymerization of 3,3-bis(azidomethyl)oxetane (BAMO) was studied, initiated by a mixture of boron trifluoride diethyl etherate/diethylene glycol (2,2′-oxydiethanol). The copolymerization of BAMO with 3-azidomethyl-3-(2,5-dioxaheptyl)oxetane (AMDHO) and 3-azidomethyl-3-(2,5,8-trioxadecyl)oxetane (AMTDO) was investigated in order to obtain at the same time a decrease of the crystallization tendency and of the glass transition temperature of poly(BAMO). The interest in this copolymerization is linked with the fact that, when BAMO was copolymerized with 15 wt.-% of AMTDO, it was possible to obtain bifunctional oligomers with a glass transition temperature in the -50 to -60°C range, without significant loss in the nitrogen content.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 166
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 959-966 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The composition of the copolymers of maleic anhydride (MA) with ethyl cinnamate (EC) and with anethole (ANE) polymerized in chloroform solutions with a radical initiator is reported. A strong alternating tendency is observed in the ANE-MA copolymer but EC is incorporated dominantly into the EC-MA copolymer. Both ANE and EC form 1 : 1 charge-transfer complexes with MA with the equilibrium constants determined to be 0,0845 and 0,026 L/mol, respectively. Applicability of the terminal, the penultimate and the complex participation models of the copolymerization mechanism is examined by non-linear least-square minimization technique using the most general forms of the composition equations. The complex participation model is found to be slightly in favor for both EC-MA and ANE-MA copolymerizations in CHCl3.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 167
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 967-979 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The synthesis, solubility, and thermal behavior of soluble, fusible, liquid-crystalline derivatives of poly(1,4-phenylenevinylene) (1) is described. The improved solubility and fusibility were accomplished by reducing interchain interactions without change of the rigid rod-like character. The interchain interactions were lowered by decreasing the structural regularity of the repeating units. The synthesis of derivatives of 1 was accomplished by the palladium-catalyzed coupling of dihalogenoarenes and ethylene to avoid cis-vinylene units. Irreversible crosslinking was observed from fusible products on annealing above the softening point.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 168
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The synthesis and characterization of new homopolymers and copolymers containing π-extended (azomethine) active moieties separated by flexible methylene spacers are reported. All synthesized monomers and polymers show spectroscopic properties (nuclear magnetic resonance, infrared, ultraviolet) in accordance with the proposed structures. The inherent solubility of the polymers in common organic solvents permits the determination of the molecular weight distribution from gel-permeation chromatography. The thermal characteristics of the polymers are also described.
    Zusätzliches Material: 1 Tab.
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  • 169
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1025-1032 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polyimides were prepared from the reaction of two aromatic dianhydrides with two diamines containing carbonyl and ether connecting groups between the aromatic rings. The diamines were prepared from the reaction of 4-aminophenol or (3-aminophenol) with an activated aromatic difluoro compound (4,4′-difluorobenzophenone) in the presence of potassium carbonate. Some of these polyimides were shown to be semicrystalline as evidenced by wide-angle X-ray diffraction. Glass transition temperatures were observed between 203 and 242°C. All polyimides were found to be thermally stable up to 400-450°C with a char yield of about 50-60% at 900°C. The effect of the structure on the properties of polyimides, such as crystallinity, glass transition temperature and thermal behaviour, is discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 170
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1059-1065 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The catalyst NdCl3/EtOH/TiCl4 (NSC) was prepared using NdCl3 as carrier. The composition of the NSC was analyzed by IR, XPS, GC and titration. This catalyst and MgCl2/EtOH/TiCl4 catalyst (MSC) were employed for the polymerization of ethylene and propene. The titanium component in NSC exists basically as Ti(OEt)Cl3 but both as TiCl4 and Ti(OEt)Cl3 in MSC. NSC combined with organoaluminium compounds polymerizes ethylene with fairly high productivity. Both the activity and the concentration of active centres C* in ethylene polymerization with NSC-AlEt3 catalyst system decrease with increasing temperature, while the propagation rate constant kp increases. The difference in the kinetic behavior for polymerization of ethylene between the NSC-AlEt3 and the MSC-AlEt3 catalyst system would arise mainly from the different stability and reactivity of the titanium active center. The activity for polymerization of propene by using NSC in comparison to MSC is very low.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 171
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1085-1090 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The feasibility of applying the method of factor analysis to X-ray diffraction diagrams of binary blends of polypropylene and ethylene-propylene-diene terpolymer (PP/EPDM) was examined. The result of mathematical treatment was satisfactory. The number of scattering species and their concentrations in six kinds of PP/EPDM blends were determined. The separation of the spectral peaks of each species in the blends, contributing spectral intensities, was carried out.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 172
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1107-1114 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Microcapsules were prepared by a coupling reaction of disuccinimido 4,4′-azobis(4-cyanovalerate)Systematic name: 5,5′-bis(imidooxy)-2,2′-dimethyl-5,5′-dioxo-2,2′-azodipentanenitrile. with L-lysine, and/or polyallylamine in a water/oil emulsion system. The microcapsules show a light-responsive release of an inner content, succinylated bovine serum albumin, to the outer bulk phase. Effects of the composition of the coupling suspension on the photo-durability of the microcapsules obtained were examined. The microcapsules would be useful as a device of photo-responsive systems.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 173
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1139-1145 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: New thermotropic liquid-crystalline (LC) copoly(urethane-carbonate)s (4) with high inherent viscosities were prepared by melt polycondensation from 6,6′-(4,4′-biphenylylenedioxy)dihexanol (1) and a mixture of aliphatic bis(phenyl carbamate)s (2) and bis(phenyl carbonate)s (3) in high yields. The polymers characterized by FTIR spectra and elemental analyses show good solubilities in organic solvents such as chloroform. Flexible films were cast from the polymer solutions. Their thermotropic LC properties were evaluated by differential scanning calorimetry and observation under the polarizing microscope equipped with a hot stage. These measurements indicate that the polymers form stable LC mesophases and possess block-like sequence distributions.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 174
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1177-1181 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The method formerly used to determine the crystallite core size of polyethylene was applied to poly(tetrahydrofuran) (PTHF). This method is based on the different diffusivity of a chaincleaving agent in crystalline and amorphous parts of the polymer. Butyllithium was used as a cleaving agent of PTHF. The degree of polymerization of the undecomposed part of the polymer (PTHF crystallites) was determined by gel permeation chromatography. This value agrees well with the value to be expected from the size of the crystallites determined small-angle X-ray scattering.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 175
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1207-1212 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The cationic polymerization of methoxyallene (1) was carried out with some Lewis acids at -50°C in dichloromethane. BF3OEt2 was found to be an effective catalyst for the cationic polymerization of 1. From analyses of 1H and 13C NMR spectra, the obtained polymers consist of units with the 1,2-double bond of 1 being opened, although the 2,3-double bond is consumed also to an amount of 24 to 43 mol-%. This decrease in 2,3-double bond content in the polymer may be attributed to intramolecular cyclization of the propagating cation and/or the intermolecular reaction of the propagating cation with polymer to produce a graft polymer. Moderately polar solvents such as dichloromethane proved to be best suited for obtaining polymers with high double bond content.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 176
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1223-1234 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Trimethylolpropane trimethacrylate (TRIM) was suspension-polymerized with toluene as poreforming agent. The concentration of the monomer (TRIM) in the porogen was varied between 20 and 50 vol.-% of the organic phase. The poly(TRIM) particles had narrow particle-size distributions. The porosity of the dry gels was studied with scanning electron microscopy, nitrogen adsorption/desorption and mercury porosimetry. All gels had bimodal pore-size distributions. The size distribution of large pores (r 〉 50 Å) of solvent free poly(TRIM) broadened when the amount of TRIM was decreased. The pore-size distributions of the swollen poly(TRIM) gel particles were calculated from size-exclusion chromatography (SEC) results. The separation range for poly(TRIM) particles of polystyrene standards varied with the monomer concentration. A relationship between the pore-size distribution of dry poly(TRIM) gels and those of swollen gels is proposed. Whether or not the structure of poly(TRIM) gels could be described as fractals is discussed.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 177
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1255-1261 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The photosensitivity in cis-polyphenylacetylene (cis-PPA, polymerized with rare-earth catalysts) can be significantly enhanced by doping the PPA with I2 or FeCl3 and sensitizing with 4-isothiocyanatofluorescein (F-II) or 2,4,7-trinitro-9-fluorenone (TNF), which are powerful sensitizers. The electrophotographic photoreceptor (P/R) device with cis-PPA + F-II (on Al substrate) appeared preferable in photosensitivity enhancement and showed good photosensitivity: dark decay 1,8 V/s; maximum rate of discharge 321 V/s; residual surface potential 22 V; discharge 89, 1%; photosensitivity 2,96 s-1. This is a new “family” of photosensitive materials which can be used in a duplicator.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 178
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1285-1296 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Initiation constant 2kd · f, dissociation constant kd, and efficiency factor f of AIBN were measured at 60°C for two model homopolymerization systems: methyl methacrylate (MMA) in N-methyl-2-pyrrolidone (NMP) and N-vinyl-2-pyrrolidone (NVP) in methyl isobutyrate (MiB) as the solvent. The stable Banfield radical was used as inhibitor. A pronounced solvent effect was observed on the side reaction of the inhibitor with the monomers. Particular solvent sensitivity of monomers in this reaction was identified, whereby opposite solvent properties of NMP and MiB as well as of MMA and NVP were found. The initiation constant 2 kd · f depends mainly on the dissociation constant of the initiator kd in regard to its solvent dependence. The efficiency factor f is influenced by monomer concentration, stability (reactivity) of primary radicals and by viscosity of the reaction medium (solvent cage effect).
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 179
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1317-1328 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A liquid-crystalline side-chain polymer with laterally incorporated naphthalene groups in the mesogenic moiety is investigated in binary mixtures with an optical uniaxial low-molar-mass liquid crystal. Mixtures with up to 50 mol-% content of the monomeric liquid crystal show a biaxial nematic phase. At lower temperatures a new biaxial smectic phase is observed, which corresponds to the smectic A phase. The angles between the optical axes are measured in dependence of temperature and mixture composition. Starting from the neat polymer, the angles decrease in the nematic as well as in the smectic phase with increasing mole fraction of the uniaxial liquid crystal. From the results a phase transformation uniaxial nematic to biaxial nematic can be inferred.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 180
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: New types of macroporous polymers containing chiral cavities were prepared for the racemic resolution of free sugars. As template monomers 6-O-methyl- and 6-O-benzyl-αD-galactopyranose 1,2;3,4-tetra-O-bis(4-vinylphenylboronate) (3c and b) as well as 1-O-methyl- and 1-O-benzyl-βD-fructopyranose 2,3;4,5-tetra-O-bis(4-vinylphenylboronate) (4c and b) were copolymerized with a large amount of ethylene dimethacrylate. After splitting off the respective templates, these polymers were used for the racemic resolution of the racemates of D,L-galactose and D,L-fructose, and also the racemates, of 1-O-methyl- and 1-O-benzyl-D,L-fructose. The polymer prepared from 3b yielded the highest selectivity for the racemic resolution of D,L-galactose. In the case of fructose the benzyl-ether-imprinted polymers yielded the highest selectivity, especially for 1-O-methyl-D,L-fructose separation. Polymers imprinted with D-galactose derivatives showed inverse selectivity by preferably absorbing L-fructose from the racemate. Polymerization at lower temperatures usually yielded more selective polymers.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 181
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1371-1385 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Macromonomers of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were synthesized by reacting the monofunctional polymer with 4-vinylbenzoyl chloride. The macromonomer was copolymerized with isoprene, butadiene, styrene, ethyl acrylate, and butyl acrylate. Reactivity ratios of 2,6-dimethylphenyl 4-vinylbenzoate (2) as a model compound were determined with styrene (St) and butyl acrylate (BA). The values obtained are rSt = 0,504, r2 = 1,233, and rBA = 0,123, r2 = 4,070. Polystyrene-graft-PPO is a one-phase system with a Tg between those of the homopolymers. Tg's of the polyacrylate and PPO fractions are not changed by the composition of the polyacrylate-graft-PPO. DSC and dynamic mechanical measurements revealed that the polyacrylate-graft-PPO copolymers are phase-separated if the molecular weight of the PPO macromonomer is high enough. In thermogravimetric analysis the polyacrylate-graft-PPO shows a two-step weight, loss, one due to the polyacrylate at 380-390°C and another due to the PPO at 440-460°C.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 182
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1431-1437 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Poly(chlorophenyl methacrylate)s with varying number and positions of the chloro substituent were prepared and investigated using 13C NMR spectroscopy. The tactic sequence distribution was determined from the signals of the carbonyl carbon (pentads) and the α-methyl carbon atoms (triads). It was found that the polymers are predominantly syndiotactic with an average sequence length of between 3 and 4. The isotactic sequences accounted for a very small fraction of the polymer chain with an average sequence length of between 1,3 and 1,5. As for the signals of the aromatic carbon atoms it could be demonstrated that, depending on the substitution pattern of the aromatic ring, the sensitivity on sequence distribution was more or less pronounced.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 183
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 663-671 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A model was developed to determine the constitution of step-growth polymers synthesized from the nonsymmetric monomers XabX and YcdY under various modes of mixing. Depending upon the inherent kinetics of the system and the modes of addition of monomers, polymer constitution can be varied over wide ranges. Results are shown for single-stage polymerizations with all variations of kinetic parameters and mixing modes. The results show that the synthesis of truly “random” polymers is very difficult with this monomer system.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 184
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 693-707 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Semidilute solutions of a fraction of poly(octadecyl methacrylate) (PODMA) obtained by radical-initiated polymerization were investigated in the theta-solvent butyl acetate (BuAc) with static and dynamic light scattering (SLS, DLS, resp.) at four different temperatures between 13°C (near theta-temperature Θ) and 70°C. The molar mass of the investigated sample (PODMA 4) was 3,2 · 106 g · mol-1. A concentration region from dilute to 8 c* was covered, where c* = 1/[η] was taken as the coil overlap concentration, [η] denoting intrinsic viscosity. Above c = 3c* the DLS correlation function exhibited bimodal behaviour at all temperatures. At these concentrations one finds two “apparent” molar masses, radii of gyration and diffusion coefficients for each concentration. The smaller apparent molar masses, smaller radii of gyration and larger diffusion coefficients correspond to characteristics of the transient network. The larger apparent molar masses, larger radii of gyration and smaller diffusion coefficients may be attributed to the formation of inhomogeneities in the semidilute solution.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 185
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 721-734 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Correlations were sought between the structure of an external alkoxysilane donor and the microstructure of the polymer chain obtained by the polymerization of propene with a heterogeneous, high-activity Ziegler-Natta catalyst. Fourteen different alkoxysilanes of structure RnSi(OR′)4-n, where n = 1-3, R = n-alkyl or phenyl and R′ = C1-3-alkyl, were used as external donors. The polymers were fractionated by boiling heptane extraction. The microstructures of the polymers were studied by means of 13C NMR spectroscopy. The structure of the donor had a marked effect on the catalyst activity and isotacticity of the polymer. However, all of the alkoxysilanes tested produced qualitatively similar differences in the microstructure of poly(propylene): the size of the isotactic mmmm pentad peak varied with the donor efficiency, but the sizes of the non-isotactic pentad peaks were more or less constant relative to each other. In the boiling heptane soluble fraction, isotacticity and syndiotacticity increased and the viscosity-average molecular weight M̄v decreased when a good external donor was used in the polymerization. Results indicate that all external alkoxysilane donors tested have the same qualitative effect on active centers, and only isotacticity, i.e., the number of mmmm sequences, can be controlled by an external alkoxysilane donor. The effectiveness and selectivity of deactivation strongly depend on the structure of the donor.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 186
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1589-1599 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The modification of isotactic poly(propylene) by nitrogen plasma treatment was studied in comparison to the use of a carbon dioxide plasma, which was reported earlier. The effect of the modification was characterized with secondary ion mass spectrometry (SIMS) to a depth of 3 Å, with electronic spectroscopy for chemical analysis (ESCA) to a depth of 20 Å and with attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to a depth of 10 μm: the nitrogen plasma modification seems to be milder than the CO2 plasma treatment. Surface degradation is a minor reaction, and in an opposite manner, crosslinking and functionalization (formation of primary amino groups) are the most important reactions. Radicals, probably originating from the elimination of [methyl groups] along the polymer backbone, could induce these reactions.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 187
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Copolymerization of the water-soluble monomer acrylamide (AAM) with the oil-soluble monomer methyl methacrylate (MMA) and/or styrene (St) in inverse microemulsion initiated with 2,2′-azoisobutyronitrile was studied. It was found that the overall polymerization rate increases with increasing mole fraction of AAM in the comonomer mixture, while the composition of the product changes only slightly. The copolymerization process is a typical “dead-end” polymerization where the limiting conversion corresponds to the AAM concentration in the comonomer mixture. The concentration of MMA, resp. St at the locus of copolymerization was calculated as a function of the AAM mole fraction in the comonomer mixture.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 188
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1017-1023 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The influence of basic reaction parameters - the ratio of catalyst components, the composition of the monomer mixture and the temperature - on the progress of the copolymerization, the molecular weight and the molecular weight distribution as well as on the composition of the copolymers obtained is reported. Conversion data for the variation of the mole ratio of comonomers show a maximum for an [Al]/[V] mole ratio of approximately 7, whereas the molecular weight of copolymers is not significantly influenced. An increase in the molecular weight of the copolymers can be obtained by an increase of butadiene content in the monomer mixture. However, there is also an increasing incorporation of butadiene into the copolymer. Raising the temperature from -60°C to 0°C results in a significant decrease in molecular weight, whereas the composition of the copolymers is not significantly changed.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 189
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1041-1058 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A study of the mechanism of thermal oxidative and thermal mechanical degradation of isotactic polypropylene (PP) is reported. Size exclusion liquid chromatography has been applied to the study of molar mass distribution (MMD) of samples of PP under oxidative degradation in the presence of an incorporated organic peroxide and of samples subjected to repeated extrusion. The change in MMD of the samples of PP under controlled oxidative degradation at 230°C is explained by a random chain scission mechanism and those of the samples of PP extruded repeatedly from an extruder at 280°C can be elucidated by a mechanism of mechanical chain scission with a threshold degree of polymerization 2L, below which the chain will not undergo scission. The value of L was found to be around 500.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 190
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The influence of several parameters on the polycondensation reaction of potassium maleate and 1,4-dihalogenobutanes has been studied in 1-methyl-2-pyrrolidone at moderate temperature. The yield and molecular weight of the obtained polyesters as well as the extent of trans isomerization and the nature of chain end-groups depend strongly on the mole ratio of reagents, the nature of halogen in the 1,4-dihalogenobutanes and on the presence of small amounts of water in the reaction mixture. In particular, it has been observed that water increases the consumption rate constant of 1,4-dibromobutane but at the same time acts as a terminating agent.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 191
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1099-1106 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Spin-lattice relaxation times (T1) have been measured by 13C NMR for poly(vinyl alcohol), poly(vinyl benzoate), poly(vinyl cinnamate) and poly(vinyl acetate) in dimethyl sulfoxide as a function of temperature and concentration. As expected, T1 increases with increasing temperature and decreases with increasing polymer concentration. The influence of the microstructure (tacticity) of the polymers on the relaxation times is negligible. T1 for the methine carbon of the polymer main chain is observed to serve as a measure of the rigidity and/or mobility of the chain. Assuming isotropic motion of the polymer chains, the activation energies for the protonated carbons were determined using the calculated correlation times.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 192
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1129-1138 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The surface tensions (γ) of a branched polyethylene and two side-group liquid-crystalline (lc) polyacrylates were measured in the isotropic, nematic and smectic states by the pendant-drop method. The surface tension vs. Temperature characteristics of the lc polyacrylates studied show anomalous behaviour. The slope in the isotropic state is initially negative but changes its sign near the isotropic-nematic transition. The increase of γ with decreasing temperature is regained in the nematic phase, until at the nematic-smectic transition the surface tension of the lc polymers discontinuously jumps to higher values and shows a very low temperature coefficient. The observed features have been found to be partly in agreement with the results of surface tension measurements on low-molar-mass liquid crystals, which indicates that the surface properties of the lc polymers are governed by the mesogenic side groups.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 193
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1153-1176 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The influence of mechanical deformation on the orientation behaviour of the phenyl benzoate mesogenic groups in polyacrylate- and polymethacrylate-based liquid-crystalline (l. c.) elastomers with spacers of six methylene units is investigated as a function of temperature and time by means of linear-dichroism infrared spectroscopy. The mesogens in the polymethacrylate elastomers preferably align perpendicular to the stretching direction and show a biaxial phase with homeotropic orientation. The changes in sample geometry, especially the film-thickness variation during deformation, are studied. The orientation behaviour of the mesogens in the polyacrylate elastomers is different in the nematic and smectic phase. On stretching, the mesogens align parallel in the nematic and perpendicular to the stretching direction in the smectic phase. The orientation of a film stretched in the smectic phase, however, changes to be parallel to the stretching direction if its temperature is raised once above the smectic-to-nematic transition temperature. The dynamics of reorientation of the mesogens strongly depends on temperature. With high mobility of the mesogens no phase lag between deformation and orientation can be detected on a timescale of 100 ms. The orientation behaviour of l. c. elastomers is very complex and depends on many parameters, each of which is important.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 194
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A new procedure for the determination of the number-, weight- and z-average molar masses M̄n, M̄w and M̄z and a model molar mass distribution W(M) has been developed from measurements of the sedimentation equilibrium. The method is based on the determination of the experimentally measured reduced concentration profile by extrapolation to zero concentration and direct calculation of the molar mass distribution W(M) by nonlinear regression of the integral equation according to the Simplex procedure. Results obtained in different solvents for the well characterized polystyrene NBS 706 with broad distribution are reasonable. Generally, it can be concluded that the suggested procedure is a suitable possibility for the determination of molar mass average values and the molar mass distribution of polymers if the latter is a log-normal, Schulz-Flory or Poisson distribution.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 195
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1235-1236 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 196
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Relationships between the ratios of the mean-square radii of gyration gs and the second virial coefficients gA2 of ring-shaped and linear polymers with the degree of polymerization P of the polymer and its Peterlin exponent ε in dilute solution were derived theoretically and numerical values calculated. The second virial coefficients of ring-shaped and of linear polystyrene at 25°C in toluene were determined using light scattering. By verifying the theoretical calculation based on the experimental determination of this polymer-solvent system with light scattering and other methods reported in the literature, the agreement between theoretical calculation and experimental results is shown. The correlation equations for linear (l) and ring-shaped (r) polystyrene in toluene at 25°C A2, 1 = 8,06 · 10-3 · M0,224 and A2,r = 6,68 · 10-3 · M0,218 were obtained using light scattering.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 197
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polyesters containing 3,3′-substituted azobenzene and benzanilide moieties as a part of conformationally mobile aromatic blocks were synthesized. Polymers based on 3,3′-substituted azobenzene residues exhibit liquid-crystalline properties and unusual thermal properties such as opposite odd-even effect and unexpected cis-trans isomeric ratio of azo group. Similar polymers with an amide group between the 1,3-substituted benzene rings cannot form liquid crystals.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 198
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1307-1315 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A study was conducted of the excited states of the combination eosine/amine/iodonium salt through time-resolved laser spectroscopy, of the photolysis products formed under light exposure, and of the rates of polymerization. It allows the process to be precised and discussed. It is apparent that the iodonium salt has no effect on the initiation step of the polymerization reaction but sharply decreases the termination reactions. The formation of a complex between eosine and the iodonium salt is suggested; this complex is destroyed in the presence of amine.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 199
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1339-1347 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The copolymerization of acrylamide with methyl methacrylate or styrene in inverse microemulsion initiated by radical initiators with different solubility in water was studied in the initial stages of the reaction. It was found that the initial rate of copolymerization depends on the mole fraction of acrylamide in the comonomer mixture and is independent of the solubility of the radical initiator in water.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 200
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1361-1369 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polymers containing cinnamic acid units were obtained by chemical modification of poly(vinyl alcohol) by cinnamic acid derivatives with a carbon-carbon double bond in para position. The reactivity of the acid chloride is lowered by the inductive effect of the double bond. Polycondensation of these derivatives, when difunctional, leads to low-molecular-weight polyamides and polyesters with good yields. The introduction of acrylic or methacrylic groups on photosensitizers has also been studied, leading to monomers which can be polymerized by a radical process, or copolymerized with the previous monomers, the polymer bearing then the photosensitizer and the cinnamic double bond on the same chain.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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