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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Time resolved x-ray solution scattering measurements were made during thermal denaturation of DNA from various sources in the temperature range of 20-90°C. Preliminary results on the influence of fragement length, ionic strength, and origin of the DNA on the time course of the scattering are described. Interpretation is based on model calculations of the scattering patterns. The resluts indicate that, for long DNA fragments at very low ionic strength, the melting process is a continuous phenomenon over the whole temperature range. It is accompanied by a progressive decrease of the radius of gyration of the cross section and of the mass per unit length. For short fragments of 146 base pair nucleosomal core DNA, stiffening of the DNA appears to precede a sharp melting transition.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(oxythiocarbonyloxy-1,4-phenyleneisopropylidene-1,4-phenylene) (1) was obtained from 4,4′-isopropylidenediphenol (Bisphenol A) and thiophosgene under phase transfer conditions, using quaternary ammonium and phosphonium salts and crown ethers as catalysts. The polymer was identified by IR and 1H NMR spectroscopy, and the molecular weights were estimated from inherent viscosity measurements. The influence of catalysts, solvent and thiophosgene addition was studied in order to find the best conditions. It was found that tetrabutylammonium bromide, dichloromethane and the addition of thiophosgene at once gives the highest yields and inherent viscosities. Other catalysts and solvents were less efficient or unefficient for this reaction.
    Additional Material: 3 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1387-1397 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The classical treatment of inhibition in radical polymerization is complemented by a “sensitivity” analysis. This technique permits to establish which of the possible reactions are relevant or negligible to gain a better insight into the mechanism. The 2,2′-azoisobutyronitrile (AIBN)-initiated polymerization of vinyl acetate was studied in the presence of 5-nitrofuroic acid and 3-(2-furyl)acrylic acid as inhibitors. The monomer dependence of the ratio of rate constants for the degradative transfer and chain propagation, ktrs/kp, and the values of the stoichiometric coefficients for these inhibitors were obtained and analyzed in the light of sensitivity analysis.
    Additional Material: 6 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 31 (1986), S. 2791-2803 
    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: As large polymer samples are quenched rapidly, residual stresses (and birefringence) are frozen into the final part due to the different thermal/contraction histories of the surface and center portions. The present work on polystyrene, a continuation of earlier studies, deals with the effects of sample size and initial temperature; these results are treated with the genral theory of Lee, Rogers, and Woo. Finally, data for two other amorphous polymers, poly(methyl methacrylate) and polycarbonate, are presented; in these cases the simpler theory of Aggarwala and Saibel is used. The theories help explain the relative behavior of the three materials and are qualitatively useful. However, the compexity of the rheooptical response precludes doing a completely rigorous treatment.
    Additional Material: 10 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 24 (1986), S. 495-501 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(1,4-oxylylenethioethers) were synthesized from 2,5-disubstituted-1,4-bis(chloromethyl)-benzenes and sodium sulfide under phase-transfer conditions. The polythioethers were characterized by elemental analysis and infrared spectroscopy. The effect of the catalyst, solvent, and temperature were studied. Their glass transition temperature and thermal decomposition were determined.
    Additional Material: 1 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 26 (1988), S. 201-206 
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1599-1610 
    ISSN: 0887-6266
    Keywords: gas trasport properties ; polycarbonates ; polysulfones ; aromatic groups ; bisphenol connector groups ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect that substitution of aromatic groups on the bisphenol connector unit of bisphenol-A based polycarbonate and polysulfone materials has on their gas transport properties was assessed. Replacement of a methyl group by a phenyl ring (bisphenol acetophenone polycarbonate, PC-AP, and bisphenol acetophenone polysulfone, PSF-AP) gives a small increase in permeability coefficients with similar or slightly higher selectivity for all gases compared to bisphenol-A polycarbonate, PC, or polysulfone, PSF. Substitution of two locked phenyl rings (fluorene bisophenol polycarbonate, FBPC, and fluorene bisphenol polysulfone, FBPSF) in place of the methyl groups in the connector unit leads to permeability and solubility coeffcients that are about twice those observed for PC or PSF. Increases in permeability for the polycarbonate and polycarbonate and polysulfone materials with aromatic substitutions are related to their larger fractional free volume. FBPC and FBPSF have the largest fractional free volume and the largest permeability coefficients. Thermal measurements show that the fluorene based polycarbonate and polysulfone materials have the highest thermal and oxidative stability. Such aromatic substitutions can be useful for developing gas separation membranes to be used in harsh thermal or oxidative environments. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1577-1589 
    ISSN: 0887-6266
    Keywords: polyphenylene ethers ; gas permeation ; gas sorption ; free volume ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas transport properties of the polyphenylene ethers poly(2,6-dimethyl-1,4-phenylene oxide)PDMPO, and poly(2,6-diphenyl-1,4-phenylene oxide), PDPPO, and the thioether poly(1,4-phenylene sulfide), PPS, have been measured as a function of pressure and temperature. The PPS material and free volume correlations were used to estimate the behavior of the unavailable poly(1,4-phenylene oxide), PPO. The results show that symmetrical substitution of phenyl groups on the backbone of polyphenylene ether, PDPPO, increases the gas transport properties by one order of magnitude relative to the unsubstituted material, PPO. Symmetrical methyl substitution, PDMPO, however, increase the permeability, apparent diffusion and sorption coefficients even further. The gas transport coefficients correlate with the fractional free volume of the polymers. PDMPO has the largest fractional free volume and gas transport coefficients followed by PDPPO and the PPS. The results show that substitution of phenyl groups, which leads to polymers that have better thermal and oxidative stability than methyl substituted ones, can be a useful means for increasing free volume and gas permeability coefficients. While methyl groups appear to be more effective for the latter, the enhanced chemical stability of phenyl rings may be useful when gas separation membranes are to be used in harsh environments. © 1993 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 577-582 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Grafting of polypropylene was carried out in both boiling xylene and decalin as solvent medium with itaconic acid (2-methylenesuccinic acid) as functional polar monomer using 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (Lupersol 101) as radical initiator. It was found that the temperature influenced the percentage of monomer grafted onto polypropylene and that the amount of monomer incorporated was practically constant after 5 min. The results also show that the amount of monomer incorporated is proportional to the initial monomer concentration used in the grafting reaction, although for higher initiator concentrations a reduction in the percentage of grafting was found.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 2653-2663 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of novel polyamides containing diacetylene groups as side chains were prepared by Cadiot-Chodkiewcz-coupling of polymer precursors bearing 2-propynyloxy side groups with 4-bromo-3-butyn-1-ol. The conversion of the acetylenic groups was in the range of 87.5-96.5% depending on the chemical structure of the polymer backbone. The polymers are highly amorphous and undergo random cross-linking on heating. Thermally treated polymer films show third-order nonlinear optical susceptibility χ(3) of the order of 10-10 esu (= 10-18m5/V2).
    Additional Material: 6 Ill.
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