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  • 1995-1999  (4)
  • Life and Medical Sciences  (2)
  • epoxy resin  (2)
  • 1
    ISSN: 1042-7147
    Keywords: epoxy resin ; homopolymerization ; thermal decomposition ; combustion ; 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: Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease.The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl-amine and allyl-either bonds. With increasing temperature, saturated alkyl-ether bonds and alkyl carbon-carbon bonds are broken first, followed by the most stable alkyl-aryl bonds at T〉365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 7 (1996), S. 823-830 
    ISSN: 1042-7147
    Keywords: epoxy resin ; phosphorylated hardener ; combusion ; fire retardancy ; 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: The kinetics of curing tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) or of the mixture TGDDM/diglycidylether of bisphenol A (DGEBA) by bis(m-aminophenyl)methylphosphine oxide (BAMPO) was studied using differential scanning calorimetry. At low advancement of curing (〈50%), the low activation energy interaction between epoxy and amino groups seems to be controlled by diffusion, whereas above 50% the role of homopolymerization tends to increase and the process becomes chemically controlled.BAMPO shows a higher fire-retardant effectiveness in the mixture TGDDM/DGEBA than in TGDDM or DGEBA alone, for which the oxygen and nitrous oxide index tests suggest a condensed phase or a gas phase fire-retardant action depending on phosphorus content. An intumescent char is formed on the surface of burning fire-retarded specimens which tends, however, to be oxidized, thus reducing the fire-proofing effect at high BAMPO content.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 163 (1995), S. 538-544 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The control of P-glycoprotein (Pgp) expression in multidrug-resistant cells (MDR) is complex and may be regulated at different levels. We have investigated Pgp stability in four different human and hamster MDR cell lines. Using a pulse-chase procedure we show that Pgp half-life is between 14 and 17 h in all these cell lines when they are growing exponentially. However, in the presence of a low level of serum, Pgp half-life is increased four to sixfold. A similar effect is observed when the cell cultures are maintained in high cell density. The increased Pgp stability appears to be differently regulated as serum deprivation results in a general enhanced degradation of total cytoplasmic and membrane proteins. Moreover, the observed serum effect suggests the involvement of growth factors in the control of Pgp stability. These findings suggest that protein stability may be an important factor in the regulation of Pgp expression. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 677-684 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Ubiquitin is the most phylogenetically conserved protein known. This 8,500 Da polypeptide can be covalently attached to cellular proteins as a posttranslational modification. In most cases, the addition of multiple ubiquitin adducts to a protein targets it for rapid degradation by a multisubunit protease known as the 26S proteasome. While the ubiquitin/26S proteasome pathway is responsible for the degradation of the bulk of cellular proteins during homeostasis, it may also be responsible for the rapid loss of protein during the programmed death of certain cells, such as skeletal muscle during insect metamorphosis. In addition, alterations in the expression and regulation of ubiquitin may play significant roles in pathological disorders. For example, dramatic increases in ubiquitin and ubiquitin-protein conjugates are observed in a wide variety of neurodegenerative disorders, including Alzheimer's disease. Patients suffering from the autoimmune disease systemic lupus erythematosus generate antibodies reacting with ubiquitin and ubiquitinated histones. At present, it is not known whether these changes in ubiquitin expression and regulation initiate pathological changes in these diseases or if they are altered as a consequence of these disorders.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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