Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary A new diamine monomer, N,N′-bis(4-aminophenyl)-2,5-(diisopropoxycarbony)benzene-1,4-dicarboxamide was synthesized. Using the diamine, several alternating copolyimide precursors were successfully synthesized by its condensation polymerization with dianhydrides. The structure and properties (mechanical properties and thermal expansivity) of alternating copolyimides imidized thermally were characterized, and compared with those of the corresponding random copolyimides prepared from the copoly(amic acid)s. The alternating copolyimides exhibited relatively higher chain order and in-plane orientation in films than the random copolyimides. The higher chain order and in-plane orientation led to the higher tensile modulus and lower thermal expansivity in the alternating copolyimides. Such effect of comonomer sequence was found to be highly pronounced in copolyimides consisting of comonomers which have a large difference in the chain rigidity. It was demonstrated in this study that the formation of alternating copolyimides is a suitable route to improve the performance of properties.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1612-1112
    Keywords: Gas co-distillation ; Tobacco essential oil ; Splitless injection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The essential oils have been isolated from tobacco leaves using a simple gas co-distillation apparatus. The method involves co-distillation with water under the continuous stream of an inert gas with subsequent single solvent extraction of the distillate. The extract is analysed on GC and GC/MS in splitless injection mode without further concentration. The method was evaluated for reproducibility using n-octadecane as an internal standard. The distillation-extraction procedure was reporducible with an average deviation of ±3% for the major constituents. The present method was applied to the analyses of the essential oils of other agricultural products.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7402-7404 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have recorded the x-ray diffraction (XRD) patterns of nanometer-size W metal clusters prepared at different average cluster sizes. Nanometer-size W metal clusters were produced through a collision induced clustering mechanism of W metal atoms generated by decomposing W(CO)6 vapors. The XRD patterns clearly showed that structure changed from amorphous→face- centered-cubic (fcc)→body-centered-cubic (bcc) with increasing average cluster size. This implies that W metal clusters do not simply approach the bulk bcc structure but pass through an intermediate fcc structure before they reach the bulk structure, as predicted by Tománek, Mukherjee, and Bennemann [Phys. Rev. B 28, 665 (1983)]. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Free Radical Biology and Medicine 12 (1992), S. 245-250 
    ISSN: 0891-5849
    Keywords: 8-Hydroxy-2'-deoxyguanosine ; Autooxidation ; DNA damage ; Free radicals ; Hydroxyl free radical ; Lipid peroxidation
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 7 (1996), S. 209-220 
    ISSN: 1042-7147
    Keywords: phase separation ; morphology ; polyetherimide ; epoxy ; emi-IPN ; 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 phase separation behavior and the morphology of polyetherimide (PEI)-modified diglycidyl ether of bisphenol A (DGEBA) epoxy resin were studied using scanning electron microscopy and light scattering. Reaction kinetics, cloud point and onset of gelation were determined by differential scanning calorimeter, optical microscope and physica rheometer, respectively. The mixture of partially cured epoxy and PEI showed bimodal upper critical solution temperature (UCST) behavior. For PEI content smaller than 10 wt%, the blends exhibited a sea-island morphology formed via nucleation and a growth mechanism. Above 25 wt% PEI content, the phase separation proceeded via a spinodal decomposition mechanism and a nodular structure was formed. With PEI content between 15 and 20 wt%, dual phase morphology was observed. This morphology was formed via primary spinodal decomposition and secondary phase separation within the dispersed phases and the matrix phases formed by the primary phase separation. This morphology was presumed to be formed in the reaction-induced phase separation mechanism with the mixture showing bimodal UCST behavior. The curing temperature had an effect on the final morphology, and the modulus of PEI-modified epoxy was influenced by the phase separation.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 2807-2809 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1323-1333 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Circular dichroism, optical rotatory dispersion, and viscosity of hyaluronic acid at various solvents compositions, concentrations, and pH values have been studied. The data show a large change in the molecular properties in organic/water solvents such as ethanol, p-dioxane, or acetonitrile/water at pH ≤ pKa. At this pH range of aqueous solution, hyaluronic acid shows a CD minimum near 210 nm whereas in the presence of organic solvent it exhibits a strong negative dichroism (below 200 nm) and a positive band near 226 nm. It undergoes a sharp, cooperative transition with respect to pH and solvent. The observed CD features are assigned to the π-π* and n-π* transitions of the amide and carboxyl chromophores. The ORD results show a gradual blue shift of trough at 220 nm with increasing magnitude of rotation when the organic solvents and hydrogen ion concentrations are increased. A one-term Drude's equation was used to analyze the ORD data, and the result show a variation of dispersion parameters with different solvents in accordance with the observed CD changes. The intrinsic viscosity of hyaluronic acid in mixed solvent at pH 2.6 is lower than that of aqueous solution. All the observed property changes of hyaluronic acid are reversed on addition of foramide in mixed solvents indicating that the hydrogen bonds are involved in this transition. The observed spectroscopic and hydrodynamic features are attributed to a conformational change of hyaluronic acid in a mixed solvent involving intramolecular hydrogen bonding between the acetamido and carboxyl groups. The possible conformational state of hyaluronic acid in solution under various conditions is discussed in terms of the reported helical structure of hyaluronic acid from x-ray diffraction studies.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 0038-1101
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 0038-1101
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...