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  • Wiley-Blackwell  (704)
  • Nature Publishing Group  (84)
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  • 1
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the reaction of 2,4,6-triphenoxy-1,3,5-triazine with octylamine in N-methyl-2-pyrrolidone at temperatures between 10°C and 190°C was analyzed by HPLC. Data analysis with the help of a mathematical model showed first order kinetics in each reaction component for the three successive substitutions at the triazine ring. The calculated rate constants differ by orders of magnitude from each other, and their ratios show a pronounced temperature dependence due to the differing activation energies of 27,53 and 82 kJ · mol-1
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 2417-2423 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of substituents of several mono- and difunctional cyanates on their cyclotrimerization behaviour has been studied by several methods. Shifts of gel point and gel fractions at full conversion in dependence on the substituent were detected for coreactions of a dicyanate with monofunctional cyanates. Critical fractions of monocyanate groups in the range of 50 mol-% for the absence of gelation were measured and could be described quantitatively by a model that is based on reaction kinetics and network statistics. Reactivity differences in dependence on substituents are also reflected in the distribution of homo- and mixed trimers at full conversion of paris of different monofunctional cyanates as measured by high-performance liquid chromatography (HPLC). This distribution follows a simple binomial scheme for cyanates with equal reactivity, whereas remarkable deviations occur, if one of the monomers reacts faster than the other. Besides, a qualitative reactivity gradation of the used cyanates was found on the basis of differential scanning calorimetry (DSC) peak temperatures, where the reaction of each cyanate was catalyzed by the same amount of a certain phenol. Finally, the shift of the OH band of several phenols caused by association with cyanate groups, measured by FTIR, was related to the data obtained from gelation, trimer distribution and DSC experiments to establish an easy and reproducible method for comparing the reactivity of cyanate monomers.
    Additional Material: 9 Ill.
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  • 3
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Molecular weight distributions of branched poly(phenylquinoxa1ines) synthesized by polycondensation of aromatic bis(l,2-diamines) with bis- and tris(l,2-diketones) were calculated based on a special a-priori branching model from gelchromatographic and viscosimetric data. Under the rcactioti conditions considered random reaction of all functional groups is suggested.
    Notes: Die Molmassenverteilungen von durch Polykondensation aromatischer Bis(1,2-diamine) mit Bis- und Tris(1,2-diketonen) synthetisierten verzweigten Polyphenylchinoxalinen wurden auf der Grundlage eines speziellen a-priori-Verzweigungsmodells aus gelchromatographischen und viskosimetrischen Daten berechnet. Damit kann für die angewendeten Synthesebedingungen eine zufällige Reaktion aller funktionellen Gruppen angenommen werden.
    Additional Material: 5 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 37 (1986), S. 218-220 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: It is shown that the CN stretching band in the region 2200 to 2300 cm-1 is suitable for fast and reliable evaluation of the OCN-conversion in soluble and gelled trimerisates of aromatic cyanic acid esters. As an internal standard the aromatic CH-stretch band is used.
    Notes: Es wird gezeigt, daß die charakteristische CN-Valenzschwingungsbande im Bereich von 2200 bis 2300 cm-1 zur schnellen und sicheren Bestimmung des OCN-Umsatzes in löslichen und gelierten Trimerisierungsprodukten aromatischer Cyansäureester geeignet ist. Als innerer Standard findet dabei die aromatische CH-Valenzschwingungsbande Verwendung.
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 37 (1986), S. 715-719 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Kinetik der thermischen Polycyclotrimerisierung von 2,2-Bis(4-cyanatophenyl)propan wurde mit Hilfe von DSC und IR-Spektroskopie untersucht. Der autokatalytische Charakter der Reaktion wurde durch Modellierung der Umsatz-Zeit-Kurven bei Zusatz difinierter Mengen der nachgewiesenen Zwischenprodukte aufgeklärt. Weiterhin wurden quantitative Beziehungen zwischen Reinheitsgrad des Dicyanats, Geschwindigkeit der Bruttoreaktion, Lage des DSC-Maximums und B-Zeit gefunden.
    Notes: The kinetics of polycyclotrimerization of 2,2-bis(4-cyanatophenyl)propane was analyzed by differential scanning calorimetry and IR spectroscopy. The autocatalytic character of the reaction was elucidated by modelling the conversion-time curves of systems with definite admixtures of the found intermediate products. Furthermore, quantitative relations between the purity of the dicyanate, the rate of the brutto reaction, the temperature of the DSC maximum, and the B-time of the resin were found.
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 38 (1987), S. 16-21 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: A Monte Carlo model for the simulation of the process of network building by polycyclotrimerization of difunctional monomers basing on the reaction mechanism of the polycyclotrimerization of aromatic dicyanates was developed. The experimental dependences of the average molar mass, the mass fractions of the first oligomers and of the gel fraction on the conversion of functional groups, measured for the reaction of 2, 2-bis(4-cyanatophenyl) propane in bulk, can be well fitted by the model. Furthermore, the possiblities of the simulation of intramolecular cyclizations and substitution effects are discussed.
    Notes: Auf Basis des Reaktionsmechanismus der Polycyclotrimerisierung aromatischer Dicyanate wurde ein Monte-Carlo-Modell zur Simulation der Netwerkbildung durch Polycyclotrimerisierung difunktioneller Monomere entwickelt. Die experimentell ermittelten Abhängigkeiten der mittleren Molmasse, der Massenanteile der ersten Oligomere und des Gelanteils vom Umsatz der funktionellen Gruppen bei der Reaktion von 2, 2-Bis (4-cyanatophenyl) propan in Schmelze werden durch das Modell gut erfaßt. Weiterhin werden Möglichkeiten der Simulation von intramolekularen Cyclisiierungen und Substituenteneffekten diskutiert.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 46 (1995), S. 241-246 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Chemical as well as structural modifications of highly branched polycyanurates can be achieved by using the reaction of dicyanates with monofunctional phenols. The key products of this reaction are iminocarbonic esters formed by addition of cyanato and phenolic groups. Two mechanisms are discussed for the second reaction step: an addition of two cyanato groups and an iminocarbonic ester (Route A) and a stepwise addition of iminocarbonic esters (Route B). The crucial difference between the two reactions is the number of abstracted phenolic groups per formation of one triazine ring: one for Route A and three for Route B. The effects of these reaction mechanisms on the gelation behavior and network buildup are studied theoretically with the help of cascade theory as well as experimentally by the reaction of dicyanate of bisphenol A with five different monophenols. The results clearly show that only with a model which is based on Route B can both the critical conversions at the gelation threshold and the gel fractions be modeled quantitatively. Furthermore, phenols with low pKa values were found to have an increased tendency of incorporation into the network.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 35 (1984), S. 212-215 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The Kuhn-Mark-Houwink-equations and the n-, w- and z- averages of the mean square end-to-end distance of linear poly(phenyl quinoxalines) with Schulz-Flory-molecular weight distributions are calculated based on measurements of intrinsic viscosities and molecular weight averages.
    Notes: Aus Messungen von Grenzviskositäten und Molmassenmittelwerten werden die Kuhn-Mark-Houwink-Gleichungen sowie die n-, w- und z- Mittel des quadratischen Endpunktabstands für lineare Polyphenylchinoxaline mit Schulz-Flory-Molmassenverteilungen berechnet.
    Additional Material: 2 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 35 (1984), S. 161-166 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Molecular weight distributions and the Kuhn-Mark-Houwink equation for linear polyphenylquinoxalines are calculated by application of four different GPC-calibration methods useful for broadly distributed molecular weight standards. In good agreement of the results Schulz-flory distributions are obtained.
    Notes: Die Molmassenverteilungen und die Kuhn-Mark-Houwink-Gleichung für lineare Polyphenylchinoxaline werden durch Anwendung von vier verschiedenen GPC-Eichverfahren für breit verteilte Molmassenstandards berechnet. In übereinstimmung der Ergebnisse der Verfahren werden Schulz-Flory-Verteilungen erhalten.
    Additional Material: 4 Ill.
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  • 10
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Separation of oligomeric trimerisates of difunctional aromatic cyanic acid esters is shown to be possible by the HPLC-gradient-elution-technique in THF/H2O on RP8-modified silicagel phases. The stepgrowth mechanism of the polycyclotrimerisation reaction was supported by quantitative analysis.
    Notes: Durch Gradientenelution in THF/H2O an RP8-modifizierten Kieselgel-Phasen gelingt eine Auftrennung oligomerer Trimerisate difunktioneller aromatischer Cyansäureester. Der Stufenmechanismus der Polycyclotrimerisierung wird durch quantitative Auswertung bestätigt.
    Additional Material: 4 Ill.
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