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  • Chemistry  (18)
  • Amino Acid Sequence
  • Wiley-Blackwell  (18)
  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 7 (1980), S. 35-40 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A pseudoracemic technique utilizing a stable isotope in one enantiomer was employed for the simultaneous determination of (R) and (S)-warfarin from plasma of human subjects. The assay includes high performance liquid chromatographic clean-up prior to mass spectral analysis to eliminate ion interferences from either co-administered drugs or contamination of the source. The assay is reliable, accurate and precise to within 5% at the submicrogram level.
    Additional Material: 3 Ill.
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  • 2
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The conformational and enthalpic changes that occur in poly(vinyl chloride) (PVC) glasses that have been vitrified from the melt under pressure have been examined by Fourier transform infrared spectroscopy and quantitative differential scanning calorimetry. It is shown that these pressures freeze in the high energy states that are characteristic of the vitrification temperature and increase the apparent glass transition temperature of the polymer. In addition, pressures in excess of the vitrification pressure, cause intermolecular effects that can be relaxed out below Tg. Both of these processes create characteristic endothermic and exothermic changes in the apparent heat capacity of the glass that appear over a period of time and are sensitive functions of the glass formation. processes as well as the subsequent annealing history. The endothermic events are interpreted as the stress perturbed volumetric relaxation process while the exotherms are associated with the release of the frozen in stresses.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 21 (1981), S. 1181-1187 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The conformational and enthalpic changes that occur in poly(vinyl chloride) (PVC) glasses that have been vitrified from the melt under pressure have been examined by Fourier transform infrared spectroscopy and quantitative differential scanning calorimetry. It is shown that these pressures freeze in the high energy states that are characteristic of the vitrification temperature and increase the apparent glass transition temperature of the polymer. In addition, pressures in excess of the vitrification pressure, cause intermolecular effects that can be relaxed out below Tg. Both of these processes create characteristic endothermic and exothermic changes in the apparent heat capacity of the glass that appear over a period of time and are sensitive functions of the glass formation processes as well as the subsequent annealing history. The endothermic events are interpreted as the stress perturbed volumetric relaxation process white the exotherms are associated withh the release of the frozen in stresses.
    Additional Material: 11 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 14 (1970), S. 2697-2706 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A survey of viscoelastic data on amorphous polymer melts indicates that the steady-state shear compliance, Je, of many systems can be approximated from a knowledge of their flow response. For systems with monomodel molecular weight distributions, the absolute value of the reduced complex viscosity, η*/η0, is found to equal 0.67 ± 0.03 at the frequency ω, where ωη0Je = 1. This result applies to a variety of polymer systems and to a wide range of molecular weights and distributions as long as the highest molecular weight dispersion of the distribution constitutes more than 20 weight per cent of the sample. This relationship determines Je from non-Newtonian flow data and thus provides a consistent way to relate differently shaped reduced variable curves and to calculate compliances from characteristic times reported in the literature. The connection between some commonly used times and Je is given. The method of calculating Je is successfully applied to capillary measurements of melt viscosities and to characteristic times determined from steady-state shear measurements of concentrated polymer solutions.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 15 (1969), S. 809-814 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental and analytical study was made to determine how well the material functions, derived from the Spriggs four-constant viscoelastic model, could describe the rheological properties of polymer melts. Viscosity and elasticity of selected polymer melts were experimentally determined in the rotational and oscillatory modes using a Weissenberg Rheogoniometer. The Spriggs model was chosen for study because of its success in describing experimental data for polymer solutions and because of its uniqueness in combining results from molecular theory with results from the theories associated with continuum mechanics. It was found that the model provides a good description of the rheological data for polymer melts and that some of the model parameters depend upon the molecular characteristics of the polymer. Since this model contains a small number of well defined constants, it should be useful in developing dimensionless engineering correlations for the complex flows encountered in processes of industrial importance. Deviations between the theoretical and experimental results are discussed and deficiencies of the model noted.
    Additional Material: 8 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 26 (1988), S. 501-513 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The KAHR model of structural relaxation has been extended to include the effects of pressure upon the retardation times of glass-forming materials. The previously used methodology is applied with a continuous distribution of retardation times of the fractional exponential form. Several forms of the pressure dependence are examined. The combined temperature and pressure changes on structural recovery of glasses are addressed in this paper.
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 837-857 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An apparatus has been constructed that permits the measurement of time-dependent changes in pressure near the point of vitrification. The same instrument is used for measuring steady-state PVT properties, which are necessary for a proper analysis of the dynamic measurements. The former experiments are referred to as pressure-jump volume-relaxation (PJVR) measurements and serve as a direct probe of the structural relaxation process that occurs in all glasses. Experiments have been performed on polystyrene from 110 to 150°C and up to 2 kbar using pressure steps of 500 bars. The qualitative observations are analogous to those obtained at atmospheric pressure by rapid changes in temperature, namely (1) nonlinearity, (2) asymmetry, and (3) memory effects associated with complicated temperature or pressure histories. Each of these effects is accounted for semiquantitatively by a phenomenological order-parameter model that has been extended to include the effect of pressure. Deviations between theory and experiment increase as temperature and pressure increase, this being manifest mostly in a predicted recovery curve (expansion isobar) that recovers the equilibrium volume more quickly than the experimental data; the contraction isobars are in most cases predicted within experimental error. The adjustable parameters of the model are found to vary somewhat with pressure and temperature, apparently due to variations in δ and Δκ. The activation volume suggests that 10-20 monomer segments are involved in the recovery process, assuming that the activation volume itself represents only a fraction of the dynamic unit (as observed in molecular glasses).
    Additional Material: 14 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 637-655 
    ISSN: 0887-6266
    Keywords: organic-inorganic composites ; sol-gel ; TEOS ; TMOS ; SAXS ; morphology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two morphological models have been proposed to describe small-angle x-ray scattering from organic-inorganic composite (OIC) materials. The first model invokes the idea of a liquid-like arrangement among noninterpenetrating fractal clusters, and the second employs an empirical correlation function that would be expected for a bicontinuous two-phase (B2P) picture with the inorganic portion exhibiting fractal characteristics. Simulated scattering profiles have been generated for direct comparison with experimental data. The samples studied were a triethoxysilane-endcapped bisphenol A epoxide resin (EAS) reacted in the presence of tetraethoxysilane (TEOS) under slightly basic conditions, and a random trimethoxysilane-functionalized copolymer of poly(methyl methacrylate) (MMA-TMS) with added tetramethoxysilane (TMOS), reacted in an acidic medium. Each morphology model qualitatively simulates the broad scattering maximum and limiting high-angle slope commonly seen in SAXS profiles. It is concluded that the inorganic phase in the EAS hybrid exhibits particle-like characteristics at length scales less than approximately 250 Å, and the organic and inorganic components are bicontinuous at larger distances. The MMATMS composite is better described by bicontinuous organic and inorganic phases with a periodic fluctuation of about 40 Å. The scattering maximum arises either from the mean separation of particles or a dominant wavelength in a concentration fluctuation, similar to that observed for spinodal decomposition. In either case, the SAXS peak position is related to the distance between junction points of the crosslinked organic polymer. © 1995 John Wiley & Sons, Inc.
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  • 9
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In an attempt to clarify the criteria satisfied at the glass transition (Tg) the effect of pressure on Tg of polyvinyl acetate has been measured by dielectric and volumetric techniques. Dielectric constant and loss has been measured as a function of temperature (25-120°C.), pressure (0-3300 atm.) and frequency (0.06-10 kcycles/sec.). At fixed frequency the temperature at which ε″max occurs increases with pressure by 0.022°C. atm. and this value is identified with (∂Tg/∂P). The In τD (where τD is dielectric relaxation time) is linear in the pressure. This dependence of In τD on pressure is different from the dependence of In τD on (T - Tg), which can be described by the WLF equation. By assuming f = (f0 + αfΔT)/(a + bP) and using the free volume model, we find In ap = bP/(f0 + αfΔT). If a = 1, f0 = 0.025; then the calculated value of b is 3.1 × 10-4 atm., and 1/b = 3.2 × 103 atm. is the same order of magnitude as an internal pressure. Volume measurements were made by the piston displacement method and by use of an Instron tester for recording force and length. The change in compressibility at Tg was used to follow ∂Tg/∂, and ∂Tg/∂P = 0.021°C./atm. in good agreement with the dielectric measurements. It was found that the volume of the sample at the same final pressure is smaller when compressed at high temperature than at low temperatures. In other words, vitrification at high temperatures and pressures produces a more dense sample than can be achieved by compression at low temperatures and seems to be a property of many glass forming systems. These results and other examples were used to show that the application of thermodynamic equations, namely ∂Tg/∂P = TgVΔα/ΔCp, to the glass transition is justified.
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 4 (1966), S. 1015-1023 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of deuteration and of changes in solvent composition on the thermo dynamics of the helix-coil transition have been studied by calorimetric and optical measurements in the poly-γ-benzyl-L-glutamate-dichloroacetic acid-1,2-dichloro-ethanc system. For a given solvent composition, deuteration of the polypeptide and of the acid lowers the transition temperature Tc, while an increase in the volume fraction of acid in the solvent raises Tc. A rise in Tc is accompanied by a decrease in both the van't Hoff and the calorimetric heats of transition, but at different rates. The result is a temperature dependency in the Zimm-Bragg cooperation parameter σ. Possible causes of this result and its implications are discussed.
    Additional Material: 3 Ill.
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