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  • 1
    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: The kinetics of the thermal decomposition of the polyester, Laminac 4116, were investigated in air and argon at atmospheric pressure by means of a continuous recording thermobalance and by differential thermal analysis. Samples were heated from ambient temperature to 600°C. at rates of 5°/min. and 15°/min. In air and argon, decompostion commences at 200°C. and is complete at 550 and 450°C., respectively. Four modes of degradation in oxygen and two in argon are indicated from derivative plots of the thermogravimetric curves. The kinetics of reaction were evaluated by the method of Freeman and Carroll. In the presence of air, the initial stage of reaction appears to involve formation of an unstable hydroperoxide intermediate which undergoes rearrangement and degradation. The energy of activation was calculated to be 19 kcal./mole. An exotherm corresponding to this first stage of degradation is observed by differential thermal analysis. The second and third stages of reaction in air correspond approximately to the two stages in argon with respect to their endothermal nature and to the temperature regions over which they occur. Mass spectrometric and infrared analysis were employed for identification of gaseous and volatile products. The fourth stage of reaction in air appears to involve the oxidation of carbon to carbon dioxide. Mechanisms of reaction are proposed and discussed.
    Additional Material: 8 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 8 (1964), S. 2389-2398 
    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: The occurrence of nonsteady-state conditions in the melt extrusion of fibers is described. Data obtained from cinephotographs are presented which indicate that the spin line diameter at a fixed point in space can have wide fluctuations dependent upon spinning parameters. It is postulated that the interaction of an elastic bulge and variable spin line tension due to a melt inhomogeneity may be responsible for the effect. Some evidence for melt inhomogeneity is presented to demonstrate the existence of domains having flow properties different from the main mass of polymer melt.
    Additional Material: 11 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 657-666 
    ISSN: 0887-6266
    Keywords: polysulfone ; aryl nitration ; permeability ; solubility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: CO2, CH4, O2, and N2 permeability and solubility of unmodified and aryl-nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N2, O2, and CH4 do not show a systematic dependence on degree of substitution. However, CO2 solubility apparently goes through a minimum as the degree of substitution is increased. CO2 solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO2/CH4 solubility selectivity increases monotonically as the degree of substitution increases. CO2/CH4 permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2981-3000 
    ISSN: 0887-6266
    Keywords: sorption ; diffusion ; acetone ; poly(ethylene terephthalate) ; poly(ethylene 2,6-naphthalate) ; copolymers ; positron annihilation lifetime spectroscopy ; infrared spectroscopy ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) were synthesized by melt condensation. In a series of thin, solvent cast films of varying PEN content, acetone diffusivity and solubility were determined at 35°C and an acetone pressure of 5.4 cm Hg. The kinetics of acetone sorption in the copolymer films are well described by a Fickian model. Both solubility and diffusivity decrease with increasing PEN content. The acetone diffusion coefficient decreases 93% from PET to PET/85PEN, a copolymer in which 85 weight percent of the dimethyl terephthalate in PET has been replace by dimethyl naphthalate 2,6-dicarboxylate. The acetone solubility coefficient in the amorphous regions of the polymer decreases by approximately a factor of two over the same composition range. The glass/rubber transition temperatures of these materials rise monotonically with increasing PEN content. Copolymers containing 20 to 80 wt % PEN are amorphous. Samples with 〈20% or 〉80% PEN contain measurable levels of crystallinity. Estimated fractional free volume in the amorphous regions of these samples is lower in the copolymers than in either of the homopolymers. Relative free volume as probed by positron annihilation lifetime spectroscopy (PALS) decreases systematically with increasing PEN content. Acetone diffusion coefficients correlate well with PALS results. Infrared spectroscopy suggests an increase in the fraction of ethylene glycol units in the trans conformation in the amorphous phase as the concentration of PEN in the copolymer increases. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2981-3000, 1998
    Additional Material: 14 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 2063-2075 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Divalent organochromium compounds, Cr(Lig)2, often become active catalysts for the polymerization of ethylene when deposited onto an oxide carrier such as silica or aluminophosphate. Hydroxyl groups are thought to react, releasing one ligand and binding the chromium to the surface. The behavior of the catalyst is then governed by the remaining ligand and the type of carrier. In this study two types of ligands were investigated: cyclopentadienyl and its open ring analog dimethylpentadienyl. This small difference in the type of ligand produces a fundamental difference in the polymerization mechanism. For comparison the mixed ligand chromocene, with one open and one closed ligand, was also synthesized and tested for polymerization.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 5 (1994), S. 671-671 
    ISSN: 1042-7147
    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
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 5 (1994), S. 673-697 
    ISSN: 1042-7147
    Keywords: Gas sorption ; Gas transport ; Polymer membranes ; Gas separation ; 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
    Notes: This overview article discusses fundamental principles of gas sorption and transport in rubbery and glassy polymers and material selection guidelines for gas separation membranes. Comparisons between the performance of membrane-based gas separation systems and more conventional technologies in key commercial applications are provided. Companion articles in this special edition focus on state-of-the-art reviews and descriptions of theoretical and experimental developments important in the technology of gas separations using polymeric membranes.
    Additional Material: 25 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 2139-2140 
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 9
    ISSN: 0006-3525
    Keywords: antifungal therapy ; Candida albicans ; peptidic inhibitors ; peptidomimetic inhibitors ; myristoylCoA ; protein N-myristoyltransferase ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MyristoylCoA: protein N-myristoyltransferase (NMT) catalyzes the cotranslational covalent attachment of a rare cellular fatty acid, myristate, to the N-terminal Gly residue of a variety of eukaryotic proteins. The myristoyl moiety is often essential for expression of the biological functions for these proteins. Attachment of C14:0 alone provides barely enough hydrophobicity to allow stable association with membranes. The partitioning of N-myrisotyl-proteins is therefore often modulated by “switches” that function through additional covalent or noncovalent modifications.Candida albicans, the principal cause of systemic fungal infection in immunocompromised humans, contains a single NMT gene that is essential for its viability. The functional properties of the acylCoA binding site of human and C. albicans NMT are very similar. However, there are distinct differences in their peptide binding sites. An ADP ribosylation factor (Arf) is included among the few cellular protein substrates of the fungal enzyme. Alanine scanning mutagenesis of an octapeptide derived from an N-terminal Arf sequence (GLYASKLS-NH2) disclosed that Gly1, Ser5, and Lys6 play predominant roles in binding. ALYASKLS-NH2 is an inhibitor competitive for peptide [Ki(app) = 15.3±6.4 μM] and noncompetitive for myristoylCoA. Remarkably, replacement of the N-terminal tetrapeptide with an 11-aminoundecanoyl group results in a competitive inhibitor (11-aminoundecanoyl-SKLS-NH2) that is ∼ 40-fold more potent [Ki(app) = 0.40 ± 0.03 μM] than the starting octapeptide. Removal of Leu-Ser from the C-terminus generates a competitive dipeptide inhibitor (11-aminoundecanoyl-SK-NH2) with a Ki(app) of 11.7 ± 0.4 μM, equivalent to that of the starting octapeptide. A derivative dipeptide inhibitor containing a C-terminal N-cyclohexylethyl lysinamide moiety has the advantage of being more potent (IC50 = 0.11 ± 0.03 μM) and resistant to digestion by cellular carboxypeptidases. Rigidifying the flexible aminoundecanoyl chain results in very potent general NMT inhibitors (IC50 = 40-50 nM). Substituting a 2-methylimidazole for the N-terminal amine and adding a benzylic α-methyl group with R streochemistry to the rigidifying element produces even more potent inhibitors (IC50 = 20-50 nM) that are up to 500-fold selective for the fungal compared to human enzyme. A related less potent member of this series of compounds in fungistatic. Its growth inhibitory effects are associated with a reduction in cellular protein N-myristoylation, judged using cellular Arf as a reporter. These studies establish that NMT is a new antifungal target. © 1997 John Wiley & Sons, Inc. Biopoly 43: 43-71, 1997
    Additional Material: 75 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 54 (1994), S. 135-152 
    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: This work describes the effect of solvent precipitation on the crystallization behavior and morphology of nylon 6,6. We found that solvent precipitation of nylon 6,6 induces elevated crystallization temperatures upon cooling from the melt (Tmc) and highly nucleated morphologies that rival those induced by rapid, thermal reprocessing such as melt reextrusion or heterogeneous nucleating agents such as CaF2. The primary techniques used to characterize these changes in crystallization behavior and morphology were differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray scattering (WAXS). Several other supplementary techniques were employed for identifying the origin of the crystallization behavior and morphological changes after solvent precipitation. Our results are consistent with the hypothesis in which dissolved nylon reorients to form ordered H-bonded regions that later serve as nucleation sites during melt processing. Finally, (Tmc) decreased with nylon 6,6 solution concentration prior to precipitation. These results suggest that polymer entaglements in solution also affect the crystallization behavior and morphology of the solvent-precipitated nylon 6,6. © 1994 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
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