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  • 1
    Digitale Medien
    Digitale Medien
    Lyotropic mesomorphic formation of cellulose in trifluoroacetic acid-chlorinated-alkane solvent mixtures at room temperature (1981)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 19 (1981), S. 1231-1236 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Mixtures of trifluoroacetic acid (TFA)-1,2-dichloroethane (1,2-DCE); TFA-dichloromethane (CH2Cl2); and TFA-trichloromethane (CHCl3) are excellent cellulose solvents at room temperature. TFA-1,2-DCE and TFA-CH2Cl2 are superior to pure TFA. Lyotropic cellulose mesophases were obtained in (20% w/v) solutions of cellulose in these solvent mixtures. The optical and optical rotatory powers of the solutions suggest that the lyotropic mesophase of cellulose is cholesteric. This implies that cellulose molecules are arranged in helical form in these solvent systems.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1981.180190806
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  • 2
    Digitale Medien
    Digitale Medien
    Additive moduli for crosslinked epoxies (1982)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 20 (1982), S. 1269-1278 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Ultrasonic measurements were made on a series of eight crosslinked polyepoxides over the temperature range from 0 to 60°C at a frequency of 2 MHz. From these measurements the bulk (K) and shear (G) moduli were calculated. These data were then analyzed in terms of molecular component properties. Proceeding by analogy with Rao's rule for liquids, the authors found that K is not an additive property but the function U = V(K/ρ)1/2γ is an additive property. Here V is molar volume, ρ is the density, and γ is the Gruneisen parameter (for interchain vibrations). A similar relation was found to hold for shear modulus. In particular, G is not an additive property but W = V(G/ρ)1/2g is an additive property, where g = (1/2α) (∂ InG/∂T)p - 1/2 is the shear analog of the Gruneisen parameter. Using U and W, calculations were made of K and G as functions of temperature for the eight epoxies. These results agree with the measured values within the experimental uncertainty of the measurements.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1982.180200713
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  • 3
    Digitale Medien
    Digitale Medien
    A 13C NMR study of mesomorphic solutions of poly(p-phenylene terephthalamide) (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 21 (1983), S. 1825-1837 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Solutions of poly(p-phenylene terephthalamide) in fuming sulfuric acid were characterized by 13C NMR spectroscopy and solution viscosity measurements over the 2-28% w/w concentration range. The spectra showed the presence of two distinct amide carbonyl resonances at low concentration, tentatively assigned to cis and trans conformations. As the concentration increased, additional carbonyl lines were observed along with significant broadening. Peak area measurements showed that only the polymer molecules in the isotropic environments contributed to the 13C NMR spectra and a considerable amount of the polymer remained in the isotropic phase at concentrations previously considered to consist of polymer in highly anisotropic regions. Spin-lattice relaxation times were measured at six concentrations using the inversion recovery method. The aromatic carbons relaxed at a much faster rate (ca. 0.10 s) than the carbonyls (ca. 0.45 s), but the relaxation rates for both carbons were essentially constant over the concentration range, indicating that the observed isotropic phase is not affected by changes in the macroscopic solution behavior so as to alter spin-lattice relaxation mechanisms.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1983.180210918
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  • 4
    Digitale Medien
    Digitale Medien
    Mesomorphic solutions of cellulose triacetate in halogenated organic acids and mixtures of trifluoroacetic acid and dichloromethane (1981)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 19 (1981), S. 1449-1460 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Cellulose triacetate (CTA) forms liquid-crystalline solutions in trifluoroacetic acid, dichloroacetic acid, and mixtures of trifluoroacetic acid and dichloromethane. Brilliant iridescent coloration, high optical rotations, and birefringent regions with swirl-like fingerprint patterns suggested the formation of cholesteric liquid crystals. Trifluoroacetic acid-dichloromethane is a particularly excellent solvent mixture to form liquid-crystal solutions of cellulose acetate. Crude bulk viscosity measurements confirm the formation of an anisotropic phase, and the temperature dependence of the critical concentration for formation of the anisotropic phase, obtained by bulk viscosity measurements at various temperatures, provides confirming evidence. Viscosity decreases with aging, suggesting that CTA is slowly degraded in the solvents studied. This is also confirmed by optical rotatory measurements and by polarizing microscope observations. The miscibility gap is observed as a function of molecular weight, and the differences between the experimental data and Flory's prediction are discussed.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1981.180190916
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  • 5
    Digitale Medien
    Digitale Medien
    Investigation of molecular order in liquid-crystalline solutions of cellulose triacetate using PMR spectroscopy (1982)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 20 (1982), S. 1019-1028 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Liquid-crystalline solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA)-CH2Cl2, TFA-1.2-dichloroethane (1,2-DCE) solvent mixtures were examined by means of PMR spectroscopy. CTA forms both cholesteric and nematic phases in these solvents depending on the CTA concentration. In cholesteric solutions the CH2Cl2 signal is initially a singlet and then splits into a doublet. The time dependence of the splitting and the effect of CTA concentration are reported. The results suggest that the cholesteric phase slowly changes into a nematic phase in the magnetic field. The splitting of the CH2Cl2 proton signal into a doublet and the 1,2-DCE signal into a quartet are due to direct magnetic dipole-dipole interactions. Rotation of the sample in the magnetic field results in the disappearance of the doublet or quartet and suggests that the solvent molecules are originally oriented in the direction of the magnetic field. In the biphasic region, immediate splitting of the CH2Cl2 proton signal suggests that the anisotropic phase is nematic.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1982.180200610
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  • 6
    Digitale Medien
    Digitale Medien
    Anisotropic solutions of methylol cellulose (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 21 (1983), S. 515-522 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Methylol cellulose solutions in dimethylsulfoxide exhibit a viscosity maximum at 18% w/v followed by a minimum at 20%, as is characteristic of lyotropic liquid crystals. The biphasic solutions exhibit areas of clear and cloudy appearance. The latter are birefringent. The highly anisotropic solutions are uniformly briefringent and in the 25-33% w/v concentration region they are brightly colored. The optical rotations of the mesomorphic phases are high, indicating a cholesteric structure. The sign of the optical rotation depends on the solution concentration and at high concentrations (25+% w/v) varies with the area of the solution viewed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1983.180210403
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  • 7
    Digitale Medien
    Digitale Medien
    Mesomorphic solutions of cellulose triacetate in trifluoroacetic acid halogenated solvent mixtures: Phase separations and factors affecting the cholesteric pitch (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 21 (1983), S. 1079-1090 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Cellulose triacetate (CTA) forms cholesteric mesophases in trifluoroacetic acetic acid (TFA) and mixtures of TFA and CH2Cl2, 1,2-dichloroethane (1,2-DCE), and CHCl3. Cholesteric pitches and solution flow times indicate that the order of solvent powers is TFA-CH2Cl2 〉 TFA-1,2-DCE 〉 TFA 〉 TFA-CHCl3, which is the order of decreasing acidity of the solvent systems. With TFA-CH2Cl2 as solvent, the one-fourth power of the pitch varies inversely with the CTA concentration, and increases linearly with temperature. The pitch increases exponentially with time and increases faster the more acidic the solvent. In a magnetic field a cholesteric to nematic transition occurs. A minimum in solution viscosity occurs at 34% w/v of CH2Cl2 for solutions in TFA-CH2Cl2. The miscibility gap as a function of molecular weight depends on the solvent composition and is smaller the higher the acidity of the solvent. Agreement between the experimentally observed A and B points and the theoretical points is better for the Khokhlov and Semenov theory for semiflexible chains than for the original Flory theory or the Flory-Ronca modification.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1983.180210708
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  • 8
    Digitale Medien
    Digitale Medien
    Theory of emulsion copolymerization kinetics (1981)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 19 (1981), S. 939-954 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An extended Smith-Ewart theory is presented which provides a description for kinetic properties of an emulsion copolymerization system during intevals II and III (i.e., after completion of latex particle formation). Differential equations are derived specifying the time evolution of the copolymer compositions and of the copolymer sequence distributions in terms of the rate coefficients for free radical entry, exit, homopropagation, cross propagation, cross transfer, and cross termination. Solutions to these equations show how an emulsion copolymer system may be designed to give formed polymer with desired composition and/or sequence distribution functions.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1981.170190409
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  • 9
    Digitale Medien
    Digitale Medien
    Synthesis and biodegradability of amylose block copolymers (1980)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 18 (1980), S. 1967-1977 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of amylose block co-and terpolymers is described. Fully acetylated amylose triacetate was hydrolyzed by hydronium ions to give a hydroxy-terminated amylose triacetate oligomer (HATA), which was reacted with diisocyanates to produce block copolymers. Prepolymers of HATA and MDI or TDI were reacted with both hydroxy-terminated polybutadiene and polypropylene glycol to form block terpolymers. Block co- and terpolymer formation was demonstrated by intrinsic viscosity increases, gel permeation chromatographic results, and NMR and IR spectroscopy. The products were easily deacetylated by NaOMe in methanol to yield amylose block co- and terpolymers. These polymers were readily degraded by α-amylase. The enzymatic hydrolysis was monitored by intrinsic viscosity measurements. The rate of biodegradation was influenced by the DS of the amylose block and the composition of the block terpolymers.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1980.170180632
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  • 10
    Digitale Medien
    Digitale Medien
    The mechanisms of latex particle formation and growth in the emulsion polymerization of styrene using the surfactant sodium dodecyl sulfate (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 269-291 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new method is presented that provides experimental information which is qualitatively and quantitatively sensitive to assumptions made as to the mechanisms of free radical entry and of latex particle formation in emulsion polymerization systems. The method consists of (1) obtaining (by electron microscopy) the full particle-size distributions (PSDs) at several different times soon after the cessation of latex particle nucleation, (2) using these PSDs to determine the volume dependences of the various rate coefficients governing particle growth by fitting the data to the appropriate evolution equations, and (3) employing these empirical rate coefficients to find that time dependence of the nucleation rate which fits the early-time PSD (again using the evolution equations). This method is quite sensitive to mechanistic assumptions: for example, one is able to determine whether or not the nucleation rate is an increasing or decreasing function of time. The technique is applied to a styrene nucleation system employing sodium dodecyl sulfate as surfactant at well above the critical micelle conventration. The data cannot be fitted even qualitatively by a simple one-step nucleation mechanis, whether it involes micellar entry or homogeneous nucleation. It is found, on the other hand, that the results can be accurately fitted by assuming that coagulation events between primary colloidal particles, perhaps formed by homogeneous nucleation, dominate both the nucleation process and the entry of free radicals into mature latex particles. In addition, the data indicate that the rate of free radical entry into the latex particles decreases with increasing particle size, at least for particles of unswollen radius less than ca. 40 nm.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1983.170210126
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