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  • 1
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Proton magnetic resonance data have been obtained for 6-methyl-2′-deoxyuridine (dT*), its 3′- and 5′-monophosphates, and its 3′,5′-diphosphate, as well as for the corresponding thymine derivatives. The synthesis of the dideoxynucleoside monophosphates - d(TpT), d(T*pT), d(TpT*), and d(T*pT*) - was accomplished, and spectral data were obtained for these four dimers. The data show that the 6-methyluracil base prefers the syn conformation about the N-glycosyl bond at the monomer and dimer levels. The presence of the syn base leads to increases in the cis couplings of the sugar ring, J1′2″ and J2′3′, which indicate a trend towards eclipsing of the substituents on the C1′-C2′ and C2′-C3′ fragments. This trend is discussed in terms of changes in the pseudorotational parameters which describe the pucker of the ring. The syn base destabilizes the g+ conformer about the C4′-C5′ bond, leading to a preference for the t conformer in all dT* residues at the monomer and dimer levels. Preliminary work on the formation of cyclobutane-type photodimers in d(T*pT) and d(T*pT*) is discussed and presented as evidence for the capability of the syn 6-methyluracil base to form base-stacked complexes.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 2
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The geminal and vicinal 13C-31P coupling constants have been monitored, as a function of pH, for a series of uracil and cytosine 3′- and 5′-nucleotides with a ribose, arabinose, or 2′-deoxyribose sugar. Data were also obtained for two 3′,5′-diphosphates in the ribose and arabinose series. The geminal J(C5′-P5′) and J(C3′-P3′) couplings show only a small dependence on the ionization state of the phosphate, decreasing by 〈 0.5 Hz in the pH 5-7 range. For the ribose and arabinose 3′-nucleotides, the vicinal J(C4′-P3′) increase (up to 1.5 Hz) on secondary phosphate ionization in the pH 5-7 range, whereas their J(C2′-P3′) couplings decrease (up to 1.5 Hz) over the same pH range. In contrast for the 2′-deoxyribose molecules, both couplings decrease (∼0.5 Hz) on phosphate ionization. The titration curves provide information about the influence of the sugar on the conformation about the C3′—O3′ bond. Some conformational trends could be rationalized by consideration of the sugar-puckerdependent contact interactions between the 3′-phosphate and the substituents on the furanose ring.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 186 (1985), S. 191-201 
    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 crystallinity and radiation crosslinking on the water induced depression of the glass transition temperature in Nylon 4 [poly(2-pyrrolidone)] has been investigated by differential scanning calorimetry. Radiation crosslinking was effective in preventing exothermic events associated with crystallization during the measurement of the incremental change in heat capacity (ΔCp); a parameter necessary for the theoretical evaluation of the depressed glass transition temperature. ΔCp, when normalized to account for fractional crystallinity, was found to deviate substantially from a linear two phase relation. A simple three phase representation of morphology is proposed to account for this deviation, and assumptions have been made regarding the distribution of plasticizer, leading to good agreement between the theoretical and experimentally observed depressions of the glass transition temperature.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1495-1508 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A series of liquid-crystalline polystyrene derivatives with ω-(4-(4-fluorophenylazo)phenoxy)-alkoxy pendant groups have been synthesized and characterized. Homologues with four or more methylene units in the spacer chain exhibit smectic liquid-crystalline phases, while the homologue with three methylene units forms an amorphous glass. The smectic A-isotropic (SA-I) transition temperatures show a marked odd-even effect as a function of the parity of the spacer chain. This odd-even behaviour is also found in the variation of ΔS/R at the SA-I transition across the series. A marked hysteresis between the transition temperatures determined on heating and the transition temperatures determined on cooling is observed. A molecular interpretation of these phenomena is proposed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The crystalline structure and the melting behavior of vinylidene fluoride/vinyl fluoride (VF) copolymers are reexamined. For copolymers containing even a small mole fraction of VF units (≍ 12%) a structure similar to the β-form of poly(vinylidene fluoride) and to the crystalline structure of poly(vinyl fluoride) is stabilized. Combined wide-angle X-ray scattering, differential scanning calorimetry and dielectric measurements show that in contrast to other vinylidene fluoride copolymers, no crystal-crystal transition below the melting region is present.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 6
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The Miscibility in blends of poly(2,6-dimethylphenylene oxide)Systematic IUPAC name: poly[oxy(2,6-dimethyl-1,4-phenylene)]. (PPO) with random or block copolymers of styrene and methyl methacrylate (MMA) was studied by light microscopy and glass transition temperature measurements. Blends of PPO and the random copolymers were found to be miscible up to a copolymer content of 18 wt.-% MMA. The transition from miscibility to immiscibility in these blends in independent of temperature in the range 100 to 350°C. From these data, the segmental interaction parameter between units of the homopolymer and MMA, χPPO/PMMA is estimated to be about 0,5. Blends of PPO and the block copolymers of styrene and MMA used behave essentially as the corresponding homopolymers in terms of miscibility.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Phase behavior in blends of random copolymers of styrene and acrylonitrile with block copolymers of styrene and methyl methacrylate was studied by light scattering, light microscopy and glass transition temperature measurements. The results are compared with those of respective blends containing random copolymers of styrene and methyl methacrylate. In terms of macrophase separation, the block copolymers display a more extended miscibility domain with styrene/acrylonitrile copolymers than the random copolymers. However, the extent of the miscibility domain varies as a function of temperature. Unlike the random copolymer blends, all blends containing block copolymers exhibit lower critical solution temperature behavior. Finally, it is established that the systems studied here undergo spinodal decomposition leading to macrophase separation.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 2111-2119 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Infrared spectra of syndiotactic polystyrene exhibiting various crystalline forms and modifications, and in the amorphous state, are reported in this contribution. In addition to strong conformational effects, the spectra demonstrate striking effects of chain packing. Several infrared spectral differences also exist between the two crystalline forms which present a trans-planer conformation of the chains. Spectral changes are also reported for solution-crystallized samples, which depend on the solvent present in the clathrate compound formed with the polymers.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 374-383 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: AC dielectric properties and thermally stimulated polarization (TSP) and depolarization (TSD) currents were studied in a series of CaCO3-filled polypropylene composites. The filler content (0 to 50 weight percent) and the average particle size (3.0 to 16.1 μm) at constant filler content (30 weight percent) were varied in separate groups of samples. In a third group of samples the filler (20 to 40 weight percent) was surface treated with stearates. The AC dielectric behavior of composites containing untreated fillers is largely determined by a small amount of adsorbed water. Upon heating, the dielectric properties show maxima (increasing with decreasing frequency) which disappear on cooling. In the case of stearate-treated fillers the dielectric loss level is higher, the dispersion and loss curves on heating reflect a combination of dipolar and protonic processes with water desorption. In the dry state the onset of an audio frequency relaxation process is observed in the pre-melting zone. The thermally stimulated currents of the composites containing treated and untreated fillers are also different. In the case of the untreated fillers the TSP curves show maxima indicating water desorption which are increasingly intense and roughly exponential with filler content. The high temperature conductivity and the intensity of the pre-melting depolarization peak pass through a minimum as a function of filler content. Above 20 weight percent filler content the activation energy of high temperature conductivity decreases. In the case of the surface treated samples, the thermally stimulated response is different for “wet” and dried samples. The dry samples exhibit a relaxation between the amorphous and crystalline transitions of the matrix polymer which is probably due to interfacial relaxation caused by the enhanced surface conductivity of the stearate-treated fillers.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 10
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Kinetic data are reported for the fast polymerization of a thermoplastic polyurethane under conditions similar to that of commercial reaction injection molding (RIM). The components were a 2000 molecular weight polyester polyol, butanediol and 4,4′-diphenylmethane diisocyanate. Three catalysts-dibutyltin dilaurate, phenyl mercuric propionate, and triethylenediamine-as well as uncatalyzed formulations were studied. Kinetic parameters were obtained by numerically fitting adiabatic temperature rise data with both second-order and hyperbolic models. The hyperbolic model gave consistently better fits and is supported by mechanistic studies in the literature. Activation energies compare well to literature values. The uncatalyzed rate was found to be significant. The kinetic parameters obtained by this method are useful measures of catalyst performance in the RIM systems. Moreover, the models provide a conveient way to predict the extent of reaction during the production of parts by the RIM process. The shape of the reaction pathway (extent of reaction time) may be important in the development of physical properties of polymers produced by the RIM process. Physical properties for these samples compare favorably to those for a conventionally produced (batch) polyurethane of the same formulation.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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