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  • 1
    Digitale Medien
    Digitale Medien
    Autoacceleration and inhibition: Free volume. Epoxy-amine kinetics (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1001-1016 
    Details
    ISSN: 0887-624X
    Schlagwort(e): free volume ; autoacceleration ; inhibition ; tertiary amines ; friction coefficient ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The epoxy-diamine cure process was studied. We found that the mechanism can be described in three steps: (i) initiation up to 20-25% of conversion. (ii) autoacceleration and (iii) inhibition. It has been observed that after the initiation there is a clear autoacceleration effect which has been explained in terms of free volume, considerations: the volume occupied by the products of reaction diminishes the available volume increasing the “local concentration” of the reactants and therefore the rate of reaction. The reaction was followed by FTIR (near infrared) as the main technique. We used a purified epoxy resin as well as phenyl glycidyl ether cured with m-xylenediamine. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1001-1016, 1998
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Synthesis of stereoregular polygluconamides from D-glucose and D-glucosamine (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 299-305 
    Details
    ISSN: 0887-624X
    Schlagwort(e): polygluconamides ; stereoregular polyamides ; stereoregular nylons ; chiral polyamides ; chiral nylons ; aminoaldonic acids ; sugar polyamides ; carbohydrate monomers ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two stereoregular polygluconamides, one (3) of polypeptide-type and the other (16) being a polycaproamide containing four stereocenters in the main chain of the repeating unit, have been prepared from D-glucosamine and D-glucose, respectively. The new polyamides were characterized by elemental analysis, and IR, 1H- and 13C-NMR spectroscopies. The molecular weights for 3 and 16 were estimated as 25,000 and 67,000, respectively, on the basis of viscosimetric measurements. Both polyamides display high optical activity; they are highly hydrophilic and readily soluble in water as well as in a variety of organic solvents including chloroform. Polyamide 16 is highly crystalline and yields resistant films with spherulitic texture. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1995.080330211
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  • 3
    Digitale Medien
    Digitale Medien
    Evaluation of intrinsic reaction constants of resonance, field/inductive and polarizability effects through molecular structures subject to protonation (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 87-104 
    Details
    ISSN: 0894-3230
    Schlagwort(e): Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: This paper reports a theoretical approach based on ab initio calculations for the evaluation of intrinsic reaction constants of resonance, field/inductive and polarizability effects of compounds subject to protonation. Field/inductive and polarizability constants can be evaluated from direct relationships between δΔEp and intrinsic contributions of the substituent. On the other hand, resonance constants should be estimated from relationships between the proton charge in the protonated molecular form and the intrinsic contributions of the substituent. It is also shown that during a protonation process the change in π charge of the carbon atom that is to bear the substituent should be the most suitable index for determining the π-electron demand of the structure concerned.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    The site of radical attack at the furan ring from MNDO calculations (1992)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Theory and Simulations 1 (1992), S. 99-103 
    Details
    ISSN: 1018-5054
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The semi-empirical SCF MNDO method has been used to calculate the radical reactivities for each reaction site in some neutral furan molecules as the average of the HOMO and LUMO probabilities both in 2pz atomic orbitals1SCF: Self-consistent field; MNDO: modified neglect of differential overlap; HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital.. The carbon atoms C5 and C2 of of the furan ring are the most favoured sites except for the furan derivatives holding a double bond in the substituent group. Also the SOMO2SOMO: Single occupied molecular orbital. probabilities of the radicals formed by addition of a hydrogen atom or a vinyl acetate model radical were calculated. Thus, once a radical is added to the C5 position the resulting radical can be partially localized on the carbon C2. Furthermore, the enthalpy of reaction for several radicals was estimated by using the calculated heats of formation of the neutral furan molecules and their radicals. The radical addition to the carbon C 5 resulted in the most exothermic reaction in comparison with other reaction sites of the molecule. However, no correlation was found between the calculated enthalpies and the degradative-transfer kinetic constants experimentally determined for the radical polymerization of vinyl acetate in the presence of the furan compounds under study.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mats.1992.040010205
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  • 5
    Digitale Medien
    Digitale Medien
    Kinetic effects on the impurities in epoxy-resin/m-xylylenediamine reaction (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 41 (1990), S. 2155-2167 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Different isolated or competitive mechanisms have been experimentally observed in order to predict the kinetics of an epoxy - amine reaction in terms of various mathematical models based on different possibilities of reaction. Impurities such as water, glycols, and in general all donors of active hydrogen even at low concentrations significantly change the course of the reaction. We therefore decided to study the curing reaction of the epoxy resin, first as a commercial product and later purified, with m-xylylenediamine of known purity. The extent of cure has been followed and determined by differential scanning calorimetry (DSC) and infrared spectroscopy (FT-IR). Purity, epoxy content and OH content were measured by liquid chromatography HPLC and wet analysis.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1990.070410920
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  • 6
    Digitale Medien
    Digitale Medien
    Kinetic parameters in non-stoichiometric epoxy-resin/m-xylylenediamine reactions (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 533-541 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The curing reaction of bisphenol A epoxy resin has been widely studied. We have found that when initial reactants are highly pure the reaction epoxy resin/m-xylylenediamine follows a predominantly autocatalytic path independent of the temperature. The purpose of this study was to discern if the kinetic model is appliable at high values of amine/epoxy equivalent ratio. Because of the nature and reactivity of m-xylylenediamine (m-XDA), the studies were carried out at low temperatures. Also, in order to obtain information about the formation mechanism of the system, different parameters such as reaction orders, activation energies, and reaction rate variation with concentration have been studied at different (1.5 : 1, 2 : 1, and 3 : 1) amine/epoxy equivalent ratios. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1993.070470313
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  • 7
    Digitale Medien
    Digitale Medien
    Epoxy resins based on trimethylolpropane. I. Determination of chemical structres (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 55 (1995), S. 225-232 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The chemical structure of an aliphatic epoxy resin was studied by using gel permeation chromatography (GPC), Fourier transform infrared (FTIR), FTIR-TGA (thermogravimetric analysis), mass spectrometry in fast atom bombardment (FAB) mode, and wet analysis. We found that when trimethylolpropane is used as starting monomer, only two OH groups are epoxidized. The resin and its different fractions have a functionality of two. Under the conditions of synthesis used by the supplier, three main products were found with masses of 246,339, and 430. No trifunctional product was detected. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1995.070550205
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  • 8
    Digitale Medien
    Digitale Medien
    Study of the thermal degradation of poly(N-vinyl-2-pyrrolidone) by thermogravimetry-FTIR (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 485-493 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The thermal degradation of poly(N-vinyl-2-pyrrolidone) (PVP) was studied by dynamic thermogravimetric analysis (TGA) in the range 200-600°C under nitrogen and oxygen atmospheres at various heating rates. The apparent activation energy of the degradative process was determined by the application of kinetic treatments, giving an average value of 242 kj/mol in N2, whereas in the presence of oxygen, two trends may be considered: At relatively low temperatures (200-400°C) and degrees of conversion, α, lower than 0.5, we obtained an average value of 199 kj/mol, whereas in the temperature interval 400-600°C with degrees of conversion higher than 0.5, the value of Ea was 306 kj/mol. Isothermal experiments carried out in N2 in the interval 350-400°C gave an average value of Ea = 231 kj/mol, in good agreement with that obtained from dynamic treatments. The FTIR spectra of the volatile compounds evolved in degradation experiments carried out in N2 as well as in the presence of oxygen suggest that PVP is thermally degraded, predominantly, by the release of the pyrrolidone side group and the subsequent decomposition of polyenic sequences. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1993.070500312
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  • 9
    Digitale Medien
    Digitale Medien
    Epoxy resins based on trimethylolpropane. II. Kinetic and thermodynamic parameters of cure withm-XDA (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 55 (1995), S. 1507-1516 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A study of cure of an epoxy resin based on trimethilolpropane (TMP) used as supplied and in purified form and m-xylylenediamine (m-XDA), as curing agent has been carried out. Thermodynamic functions such as activation energy, activation entropy, activation enthalpy, and free energy of activation were determinated. From kinetic study we have observed that there are two competitive mechanisms; autocatalyzed and n order, with the values of activation energy ranging between 52.9 and 64.6 kJ/mol. The overall order of reaction is found to be 2.5, and the order of reaction with respect to the hydroxyl group is clearly determined and equal to 1. Gelation study was carried out under two conditions: isothermal and adiabatic. From isothermal study we obtained the values of functionality of the resins (approximately two) and the apparent activation energy of the process. The adiabatic study allowed us the determination of the pot-life taking into account the theoretical model used, with reasonable theoretical/experimental agreements. The importance of n-order path for this kind of resins (with high OH contents) is well demonstrated through kinetic and thermodynamic parameters. The thermodynamic functions showed themselves as very sensitive parameters for the following and evolution of the reaction. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1995.070551102
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  • 10
    Digitale Medien
    Digitale Medien
    Measurement of yeast concentrations in liquid hydrocarbon fermentations: Influence of experimental conditions and statistical significance of the results obtained (1972)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 14 (1972), S. 609-615 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The influence of the following factors on the measurement of yeast concentration in liquid hydrocarbon fermentations was studied: surfactant, type (Tween 20, Tween 80, and G 3300), yeast concentration (0.215 to 0.272 and 3.37 to 4.08 g/liter, as dry matter), oil concentration (8.32 and 61.6 g/liter), surfactant, concentration (0.515, 1.030, 1.545, and 2.060 g/liter), and time of contact of the surfactant with the oil-yeast-aqueous medium mixture (2 and 10 min). The statistical significance of the obtained results was determined.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260140406
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