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  • 1
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Copolymers of glycine and β-alanine within a range of amount-of-substance compositions from 3:1 to 1:9 were prepared by polycondensation of mixtures of the respective pentachlorophenyl ester hydrobromides. Number-average molecular weights between 2 500 and 9 000 were obtained, the lower values corresponding to those copolymers with a higher content in glycine. Sequence distributions were evaluated by means of 50,3 MHz 13C NMR spectroscopy and the crystalline structure was examined by wide-angle X-ray diffraction. Random copolymers having similar contents in glycine and β-alanine were found to crystallize in a bidimensional hexagonal lattice (a = 4,79 Å) with chains packed in a similar manner as they do in the crystalline structure of polyglycine II. On the contrary, a heterogeneous product consisting of homopolymer and random copolymer fractions results from mixtures which are enriched in one of the two amino acids. The random copolymer poly(glycine-ran-β-alanine) adopts a packing scheme similar to that found for the helical form of the alternating copolymer nylon 2/3. Chains are hexagonally arranged and interlinked by a three-dimensional network of hydrogen bonds as described for the well known model of polyglycine II, although in the present case no order along the chain axis should be expected.
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A combined X-ray diffraction and electron microscopy study was carried out on both the solution-grown crystals and oriented films of nylons 3/5/7 and 7/5/3. These regular odd-odd-odd terpolyamides have such sequence of amide groups along the chain that they have to be aligned parallel in order to form every hydrogen bond without strain. It was found that a layered α-structure with hydrogen-bonded sheets made up of parallel chains in fully extended conformation is adopted in both cases. These results are not necessarily generalized to odd-numbered nylons where an antiparallel alignement of chains is compatible with the formation of hydrogen bonds. Chain-folded lamellar crystals obtained from solution were investigated by electron diffraction and their surface topology examined by polymer decoration with polyethylene. A bimodal orientation of hydrogen-bonded sheets within the lamella is assumed to occur in order to account for the obtained decorating patterns. Either way, chain foldings are not contained in such sheets but intersect them at an angle of about 60°.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 194 (1993), S. 3377-3383 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Metal vinyl acetate (MVAc) colloids were obtained by cocondensation at 77 K of the monomer with several metals such as: Pd, Ag, Au, Zn, Cd, Ga, In, Ge, Sn, Sb and Bi. Some of these colloids are stable for months at room temperature (Au, Ag, Pd). The colloids were polymerized with different amounts of initiator (2,2′-azoisobutyronitrile) at 65°C, and a wide range of viscosity-average molecular weights (104 〈 M̄v 〈 106) were obtained depending upon the metal used. The particle size of these clusters dispersed in the polymer matrix is around 1400 Å. The polymers are stable even at 320°C, and the metal content is ranging from 0,01 to 0,96 wt.-%. The color of the polymers depends upon the metal used.
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  • 4
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Einige Festkörperrcaktionen. die zur Bildung von Polymer-Kristallen führen. werden diskutiert und es wird gezeigt, wie man die Ergebnisse der morphologischen Untersuchungen dazu verwenden kann, den Mechanismus der Festkörperpolymerisation aufzuklären. Beispiele für die folgenden drei Mechanismen werden im einzelnen behandelt: (a) Kristallisation der makromolckularen Ketten nach der Polymerisation, (b) simultane Polymerisation und Kristallisation, (c) Polymerisation in fester Lösung.Als ein Beispiel für Kristallisation nach bereits erfolgter Polymerisation wird die Morphologie von Ziegler-Natta Olefin-Polymerisaten diskutiert. Ein anderes Beispiel dafür liefert die kationische Polymerisation von 1,3,5-Trioxan aus Lösungen. Es wird gezeigt. daß in diesem Fall das System einem thermodynamischen Gleichgewicht zwischen der kristallinen Phase des Polymeren und dem gelösten Monomeren zustrebt. Dabei findet durch Aufbrechen der Kettenfalten und Einbau von Monomereinheiten ein Dickenwachstum der Kristalle statt, das schließlich zur Entstehung von gestrecktkettigen Kristallen durch diese Transacctalisierung führt.Die durch Bestrahlung oder katalytisch induzierte Festkörperpolymerisation von 1,3,5-Trioxan oder 1,3,5,7-Tetroxan stellt ein Beispiel für simultane Polymerisation und Kristallisation dar. Einige molekulare Modelle für das Wachstum der Ketten werden auf Grund der morphologischen Beobachtung entwickelt. Es zeigt sich, daß bei diesen Reaktionen im allgemeinen keine wirklichen gestrecktkettigen Kristalle des Poly(oxymethylen)s. (POM) entstehen; Ursache dafür ist entweder Kettenfaltung (Dichtefluktuation entlang der Faserachse) oder Zwillingsbildung (Orienticrungsfluktuation). Art und Ursprung der Zwillingsbildung von POM aus kristallinem 1,3,5-Trioxan wird im einzelnen erörtert.Die topochemische Polymerisation von Monomeren mit konjugierten Dreifachbindungen gibt ein Beispiel für Polymerisation in fester Lösung. Die Polymerketten wachsen als isolierte Einheiten im Gitter des Monomeren. In einigen Fällen kann das gesamte Monornere ohne Phasentrennung umgesetzt werden. Dadurch entstehen makroskopische Polymer-Einkristalle aus gestreckten Ketten. die bisher noch nicht auf andere Weise dargestellt werden konnten.
    Notes: Some solid-state reactions which give rise to the formation of polymer crystals are discussed and the observation of the nascent polymer morphology is used as a guide-line to learn about the reaction mechanism of solid-state polymerizations. Examples for the following three different mechanisms are treated in detail: (a) crystallization succeeding polymerization, (b) simultaneous polymerization and crystallization, and (c) polymerization in solid solution.The nascent morphology of poly(alkylene)s obtained by Ziegler-Natta catalysis is taken as an example for crystallization succeeding polymerization. Another example is the cationic polymerization of 1,3,5-trioxane from solution. In this case a thermodynamic equilibrium between the phases of the solid crystalline polymer and the dissolved monomer is approached; here, by breaking up chain folds and insertion of monomeric units, an increase in thickness of the crystals takes place, which finally leads to extended chain crystals by this transacetalization.The solid-state polymerization of 1,3,5-trioxane and 1,3,5,7-tetroxane as induced by high-energy radiation or catalysts is described as an example for simultaneous polymerization and crystallization. Possible molecular models of the chain growth are developed on the basis of the morphological observations. Truly extended chain crystals of poly(oxymethylene), (POM), cannot be obtained generally from solid 1,3,5-trioxane or 1,3,5,7-tetroxane; the reason for this is either chain-folding (density fluctuation along the fibre axis) or “twin”-structure formation (orientation fluctuation). The nature and origin of the “twin”-structure of POM from crystalline 1,3,5-trioxane is discussed in detail.Topochemical polymerization of monomers with conjugated triple-bonds is an example for polymerization in solid solution. The polymer chains grow as isolated macromolecules within the monomer lattice. Since quantitative conversion can be reached in some cases without phase separation, this comprises a method to produce macroscopic, extended chain polymer single crystals, which so far could not be prepared by another method.
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  • 5
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The nascent crystal structure and morphology of poly(oxymethylene) (POM) obtained from 1,3,5-trioxane crystals, induced by gaseous chemical initiators, was studied in order to clarify the solid-state polymerization mechanisms of this monomer. The polymerization starts at the surface of the monomer crystals and propagates towards its interior. The polymerization rate, therefore, depends on the size of the crystals and not on the initiator amount. Hexagonal fibrous crystals without a main orientation were obtained on the surface of the monomer crystal. These crystals orientated themselves along the c-axis of the monomer, due to the polymerization propagation inside the crystals by simultaneous solid-gas polymerization and crystallization mechanisms. The orientation depended on the reactivity of the initiator, the order being: BF3-O(C2H5)2 〉 SnCl4 〉 H2SO4-paraformaldehyde. The orientation was also improved by increasing the polymerization temperature, obtaining POM crystals similar to those found by radiation induced polymerization. At low polymerization temperature folded chain crystals were obtained similar to those encountered by solution polymerization according to crystallization succeeding polymerization mechanisms.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 178 (1977), S. 659-667 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The synthesis of styrene polymers containing transition metals was achieved by reaction of different polystyrenes with Mt(CO)6 or (CH3—C≡N)3Mt(CO)3, (Mt = Cr, Mo, or W). Atactic, isotactic, and cross-linked polystyrene (with divinylbenzene) were employed. Organometallic polymers with good stability were only obtained by coordination of tricarbonylchromium groups to the phenyl rings of the polystyrene. Tricarbonylmolybdenum- and tricarbonyltungsten complexed polystyrene showed very poor stability and could not be isolated. The amount of chromium incorporated depends on the molecular structure of the polymers, the chromiumcarbonyl complex used in the reaction, and the reaction time. The reactivity of the tris(acetonitrile)tricarbonylmetal-complexes is higher than that of the hexacarbonylmetal-complexes and the addition reactivity of the polymers is in the order: atactic 〉 isotactic 〉 cross-linked polystyrene
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  • 7
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In order to elucidate the reaction mechanism of the chemically induced solid-state polymerization of 1,3,5,7-tetroxocane, the nascent morphology of poly(oxymethylene), (POM) crystals was investigated. The results show that POM has a lamellar morphology consisting of folded polymer chains. This morphology is different from that of the fibrous morphology obtained by radiation induced solid-state polymerization of 1,3,5,7-tetroxocane. Based on this the reaction takes place according to a crystallization succeeding polymerization mechanism, where the monomer passes through the gasphase to reach the reaction center.
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  • 8
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The flow properties of concentrated solutions of polyarylate from bisphenol A/50:50 isophthalic acid: terephthalic acid in m-cresol are studied. The results are discussed in terms of critical concentration Cc and critical molecular weight Mc for the onset of entanglements. Values of Cc = 8,2 wt.-% and Mc ≈ 3500 are obtained. The dependence of the Newtonian viscosities with temperature allows to obtain different energies of activation of flow for each polyarylate/m-cresol system, ranging from 9 to 13 kcal/mol (= 37,7 to 54,4 kJ/mol). The following free-volume-additivity equation is proposed to fit these data: \documentclass{article}\pagestyle{empty}\begin{document}$ E_{\rm a} = \frac{{V_{\rm p} \cdot \alpha _{\rm p} \cdot E_{{\rm ap}} + V_{\rm d} \cdot \alpha _{\rm d} \cdot E_{{\rm ad}} }}{{V_{\rm p} \cdot \alpha _{\rm p} + V_{\rm d} \cdot \alpha _{\rm d} }} $\end{document} where Ea, Eap, and Ead are the activation energies of the solution, the polymer and the solvent, respectively. Vp and Vd are the polymer volume fraction and the diluent volume fraction, respectively, and αp and αd represent the differences between the volume coefficients of expansion above and below the corresponding glass transition temperatures for the polymer and the solvent.
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  • 9
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 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.
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  • 10
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The radiation induced solid-state polymerization of tetroxane and trioxane was investigated. The influence of radiation-dose, reaction-time and temperature on yield and molecular weight was studied. Post-polymerization of both monomers shows a limiting conversion which increases with increasing reaction temperature. The activation energy of the post-polymerization was determined to 24 ± 2 (kcal/mole) in the case of tetroxane and was 36-38 (kcal/mole) in the case of trioxane. Time(t)-conversions(x)-curves for tetroxane could be described by the empirical equation: \documentclass{article}\pagestyle{empty}\begin{document}$$x = k_1 t/(1 + k_2 t)$$\end{document} whereby k1 and k2 are constants which could be evaluated by an appropriate plotting of the experimentally obtained data. Contrary to the post-polymerization of trioxane a pro-portionality between molecular weight, conversion and polymerization temperature was found in the case of tetroxane such that with increasing conversion higher molecular weights were obtained and an increase of reaction-temperature gave rise to higher molecular weights at constant conversion. The highest molecular weight obtained by post-polymerization of tetroxane was of the order of 8·105 and ca. 4·105 in the case of trioxane. The probability of chain-transfer is considerably higher with the polymerization of trioxane as compared with tetroxane.The morphology and texture of the originating polymers can be connected - at least qualitatively - with the reaction kinetics. It is highly probable that the kinetics of the polymerization of tetroxane are governed to some extent by relaxation processes of the growing polymer chains.
    Notes: Die strahlungsinduzierte Polymerisation von kristallinem Tetroxan und Trioxan wurde untersucht und der Einfluß von Strahlendosis, Reaktionszeit und -temperatur auf den Umsatz und das Molekulargewicht der entstehenden POM, insbesondere bei der Nachpolymerisation, studiert. Die Zeit-Umsatz-Kurven für die Nachpolymerisation laufen bei beiden Monomeren asymptotisch gegen einem Grenzwert des Umsatzes, der mit steigender Reaktionstemperatur ansteigt. Die Aktivierungsenergie der Nachpolymerisation wurde zu 24 ± 2 kcal/Mol für Tetroxan und zu 36-38 kcal/Mol für Trioxan bestimmt. Die Zeit(t)-Umsatz(x)-Kurven für Tetroxan lassen sich durch die empirische Gleichung: \documentclass{article}\pagestyle{empty}\begin{document}$$x = k_1 \cdot t/(1 + k_2 t)$$\end{document} beschreiben, wobei k1 und k2 Konstanten sind, die durch geeignete Auftragung der Meßwerte ermittelt werden können. Im Gegensatz zu Trioxan findet man bei Tetroxan eine Proportionalität zwischen Molekulargewicht, Umsatz und Polymerisationstemperatur in der Weise, daß mit steigendem Umsatz höhere Molekulargewichte beobachtet werden und bei konstantem Umsatz mit steigender Temperatur auch höhere Molekulargewichte auftreten. Bei der Nachpolymerisation von Tetroxan lagen die höchsten erreichbaren Molekulargewichte bei 8·105, während bei Trioxan nur Werte von 4·105 erreicht wurden. Die Wahrscheinlichkeit für übertragungsschritte ist bei der Polymerisation von Trioxan wesentlich höher als bei Tetroxan.Zwischen der morphologischen Beschaffenheit und Textur der entstehenden Polymeren und den kinetischen Befunden lassen sich qualitative Beziehungen herstellen. Danach wird die Reaktionskinetik im Fall der Polymerisation von Tetroxan wesentlich durch Relaxationsvorgänge an den sich bildenden Polymerketten beeinflußt.
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