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  • Physics  (55)
  • ASTROPHYSICS
  • 2020-2024
  • 1980-1984
  • 1970-1974  (55)
  • 1972  (55)
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  • 2020-2024
  • 1980-1984
  • 1970-1974  (55)
Jahr
  • 1
    Digitale Medien
    Digitale Medien
    Copolymerization of styrene and diethyl fumarate with ZnBr2. IV. Comparison between photoinitiation and electroinitiation (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 3253-3265 
    Details
    ISSN: 0449-296X
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A comparative analysis of photoinitiation and electroinitiation can help elucidate initiation processes in donor-acceptor charge-transfer copolymerization. The technique has been applied to the zinc bromide-catalyzed copolymerization of styrene and diethyl fumarate in methanol. The photocopolymer product was analyzed by GPC, NMR, and elemental analysis. The results showed that 1:1 copolymers were formed initially, but changes occurred in both the kinetics and products after the early stages of the reaction. Significant correlations found between the two initiation methods included the initial kinetic order with respect to the initiating process and the effect on product yield of equivalent increases in total initiation energy. The limiting value of zinc bromide for both initiation methods was found to be the same. The data obtained support the contention that the copolymerization proceeds through a donor-acceptor process and that photoactivation of the preformed complex, inducing electron transfer, is a likely initiation process.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.170101112
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  • 2
    Digitale Medien
    Digitale Medien
    Copolymerization of styrene and diethyl fumarate with zinc bromide. III. Electroinitiation at low current densities (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 3267-3277 
    Details
    ISSN: 0449-296X
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electroinitiated preparation of equimolar copolymers of styrene and diethyl fumarate is described. The reaction medium consisted of these monomers dissolved in a methanol-zinc bromide solution. Rates of polymerization increased with increasing applied current and the copolymer yield increased linearly with the total number of Faradays transferred. The copolymer composition is 1:1 and is essentially invariant with the degree of conversion (〈15%), electroinitiation rate, and monomer feed ratios. A reaction mechanism involving donor-acceptor complexes and electroinitiated excitation of these complexes at the electrode is postulated.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.170101113
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  • 3
    Digitale Medien
    Digitale Medien
    Structure analysis of chain-folded lamellar polyamide crystals from X-ray diffraction (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 863-875 
    Details
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Folded-chain crystals of certain polyamides present some novel diffraction effects due to the small number of repeat units within the lamellar thickness. X-ray diffraction evidence is available in the complete range from low to wide angles. This information is interpreted in terms of the structure factor of an individual lamella together with the lattice factor appropriate for the stacking of lamellae. When due account is taken of the lattice factor, whose effect can be detected even at large angles, three features of the lamellar structure can be deduced. First, the evidence is in favor of the straight-chain stems traversing almost the total thickness of each lamella, implying sharp folds at the lamellar surfaces. Some consequences of this result on the interpretation of data obtained from annealed mats are mentioned. Second, the detailed determination of the stem structure demands that the majority of the folds in nylon 66 lie in the acid group. Third, there are regions of depleted electron density at the lamellar surfaces, though features of the crystal structure are still retained. This indicates the presence of some folds deeper in the crystal than the majority.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.160100508
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  • 4
    Digitale Medien
    Digitale Medien
    Crystallization of poly(ethylene oxide) fractions: Crystallization isotherms (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 1555-1564 
    Details
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The crystallization kinetics of a range of fractions of poly(ethylene oxide) are presented and analyzed. It is concluded that deviations from the Avrami equation with exponent of 3 are mainly due to rejection of low molecular weight molecules for the low molecular weight fractions (M̄n 〈 6,000) and to a process of crystal perfecting for the high molecular weight fractions (M̄n 〉 6,000).
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.160100812
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  • 5
    Digitale Medien
    Digitale Medien
    Crystallization of polyethylene at high pressure: A kinetic view (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 1811-1836 
    Details
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A model for the crystallization kinetics of polymers is outlined and is used to interpret observations of the crystallization of polyethylene at high pressures. This model introduces a distinction between σe the lamellar surface energy which controls the lamellar thickness, and σe′, the surface nucleus surface energy which controls the growth rate. Differential scanning calorimetry and electron microscopy data for several polyethylenes crystallized at pressures of up to 8 kb are presented. From the dependence of lamellar thickness on the crystallization undercooling at 5 kb, it is found that σe increases markedly with pressure leading to the formation of very thick crystals at high pressures. The magnitude of the increase in σe is in agreement with σe values calculated from the dependence of melting temperatures on pressure. The nucleus surface energy σe′ is not expected to vary significantly with pressure, and estimates of growth rates of 5 kb which indicate that the growth rate does not vary significantly with pressure at constant under-cooling confirm this. Fractionation effects and the differences in behavior between different polyethylenes are also discussed.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.160100916
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  • 6
    Digitale Medien
    Digitale Medien
    Applications of ESCA to polymer chemistry: Studies of some nitroso rubbers (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 1637-1654 
    Details
    ISSN: 0449-296X
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular core binding energies of the polymers formed by copolymerization of CF3NO with CF2=CF2, CF2=CFCl, and CF2=CFH, respectively, have been studied by means of ESCA. The results are interpreted in terms of CNDO/2 SCF MO calculations on some model systems. Some evidence for structural irregularity is found for the copolymers with CF2=CFCl and with CF2=CFH. The reaction mechanism for the polymerization is also discussed in terms of the experimental results and INDO SCF MO calculations.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.150100606
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  • 7
    Digitale Medien
    Digitale Medien
    Surface changes during polypropylene photo-oxidation: A study by infrared spectroscopy and electron microscopyIssued as NRCC No. 12510. (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 1077-1092 
    Details
    ISSN: 0449-296X
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The surface oxidation of polypropylene films which occurs during ultraviolet irradiation in air was found to result in extensive surface restructuring. This restructuring was detected by changes in surface infrared spectra, as measured by attenuated total reflection spectroscopy, and by electron microscopy. The 997 cm-1/974 cm-1 absorbance ratio of the film surfaces increased steadily during ultraviolet degradation and was interpreted as an increase in helical ordering which resulted from backbone scission during irradiation. This scission probably also results in the increase in crystallinity detected by density changes. Electron microscopy of direct surface replicas and replicas of material detached from the oxidized film surfaces showed that surface cracking resulted during photo-oxidation, and that this oxidation penetrated selectively into the polymer structure. The replicas of detached, oxidized material showed periodic structures related to the interior morphology of the films. The observed restructuring is believed to be entirely responsible for the decrease in percentage elongation at break which results from photodegradation.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.150100412
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  • 8
    Digitale Medien
    Digitale Medien
    Viscoelastic properties of crosslinked solutions of poly(2-hydroxymethyl methacrylate) in diethylene glycol. VI. Comparison with poly(butyl methacrylate) and poly(butyl acrylate) networks crosslinked to very low degreesPaper presented at the IUPAC Symposium, Leyden 1970. (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 345-356 
    Details
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: On the basis of our own experimental and some literature data, the contributions of slow relaxation mechanisms to the shear modulus, (GeN  -  Ge), and the parameter C2 of the Mooney-Rivlin equation have been examined for lightly crosslinked poly(butyl methacrylate), poly(butyl acrylate), poly(2-hydroxyethyl methacrylate), and some rubber networks. For the rubbers, increasing degree of crosslinking caused a decrease in GeN  -  Ge and an increase in C2; for the other networks, both GeN  -  Ge and C2 diminished with increasing crosslinking. The effectiveness of the crosslinking polymerization, and also the absolute values of the physical crosslinking degree, decreased in the order of poly(2-hydroxyethyl methacrylate), poly(butyl methacrylate), and poly(butyl acrylate). The values of the equilibrium compliances J of the networks studied, obtained by various methods, have also been compared, and good agreement has been found.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.160100214
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  • 9
    Digitale Medien
    Digitale Medien
    Adsorption of polymers at the solution-solid interface. VI. Polyacids on nylon powder (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 993-1011 
    Details
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The adsorption of some polyacids, principally poly(acrylic acid), on nylon powder has been studied. In aqueous solutions at low pH the adsorption behavior of poly(acrylic acid) is controlled by adsorbate coil dimensions rather than by electrostatic effects. Less adsorption takes place from methanol solutions but the process is much more rapid than from water. Above a critical value, increase of adsorbate molecular weight leads to a reduced adsorption, the effect being particularly evidenced by aqueous solutions. Model compounds (propionic and glutaric acids) are rapidly adsorbed from both methanol and water, but give low specific absorptions. Adsorption of poly(acrylic acids) and model compounds, is reduced, but not eliminated, by modification of the nylon adsorbent through acetylation or methoxymethylation. The adsorption of poly(acrylic acid) on nylon is not readily reversible; however, partial neutralization will release preadsorbed poly(acrylic acid) from nylon powder. The adsorption behavior of copolymers of acrylic acid with N-vinylpyrrolidone is reported, as are brief studies on some other homopolyacids. The results are generally interpreted on the basis of sorption of the macromolecules into a swollen, flexible adsorbent.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.160100604
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  • 10
    Digitale Medien
    Digitale Medien
    Low-angle x-ray scattering from crazes and fracture surfaces in polystyrene (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 1565-1574 
    Details
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Both crazes and fracture surfaces in glassy polymers produce a low-angle scattering of x-rays. Scattering patterns are anisotropic and often show considerable streaking. In the one case (polystyrene) studied extensively so far, detalied analysis suggests that the craze is approximated as a collection of spheroidal or irregular-shaped voids surrounded by material with anisotropic density distribution arising from its orientation in the stress direction. The void dimension is about 90-115 Å and the specific internal surface area about 170 m2/cm3 of craze. These results and those from electron microscopic studies are reasonably consistent.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1972.160100813
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