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  • Polymer and Materials Science  (317)
  • Inorganic Chemistry  (27)
  • 1
    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: The mastication of poly(vinyl chloride) (PVC) in presence of monomers causes important changes of the thermal stability of the polymer when the last one possesses a basic character (e.g., 2-vinylpyridine). The dehydrochlorination rate is greatly increased, even if the monomer is present in only small amounts. In the most cases (styrene, acrylic ester) a better thermal stability is observed with respect to the acceleration of the dehydrochlorination, which is retarded or even suppressed. Infrared spectroscopy and differential thermal analysis show that the improved stability is due to an improved crystalline organization. When mastication causes the polymerization of the monomer (methyl methacrylate), degradation of the PVC part and depolymerization of the rafted part are observed simultaneously; this fact supports a radical mechanism for the thermal degradation of the PVC.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The synthesis of various fluorinated acrylates CH2=CHCOO(CH2)pCnF2n+1 and their kinetics of radical homopolymerization are presented. The fluoroacrylated monomers have been prepared in two steps by acrylation of the corresponding halogenated alcohols produced by radical addition of perfluoroalkyl iodides(CnF2n+1I) to ω-hydroxylated alkenes. The fluorinated acrylates differ from each other in the nature (branched or linear) and the length (n ranging from 1 to 8) of the fluorinated chain and in the nature of the spacer between this fluorinated chain and the ester group (p ranging from 1 to 11). The kinetics of polymerization led to the determination of kp2/kte. These values were compared with those of commercially available fluorinated acrylates and were found to depend upon both the spacer length and the nature of the fluorinated group.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0959-8103
    Keywords: polyurethane ; network formation ; metallic filler ; viscosity ; kinetics ; 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: The addition of metallic fillers is recognized to impart improvement of acoustic properties to polyurethane-based materials used for marine applications. The system under consideration was obtained by the reaction of a triisocyanateterminated prepolymer with 1,4-butanediol, in the presence of various concentrations of lead powder. With increasing lead content, gelation time is reduced and an Einstein-type law does not apply. The kinetics of the reaction were determined by Fourier transform infrared spectroscopy. Deviation from the classic second order is observed for the filled systems, and the higher the lead content, the more important the deviation is, showing undoubtedly the catalytic effect of the metallic powder.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Viscosity and preferential solvation measurements were carried out on maleic acid-ethyl- and -butyl vinyl ether alternating copolymers (MA-EVE and MA-BVE, respectively) in watermethanol and water-2-chloroethanol mixtures. The conformational transition of MA-BVE was found to be strongly related to the solvation of the polymer by 2-chloroethanol. Comparison of experimental results on MA-BVE, MA-EVE, and poly(methacrylic acid) (PMA) in water-2-chloroethanol mixtures indicates that the behaviour of MA-EVE is different from that of MA-BVE and PMA because it does not undergo any conformational transition.
    Additional Material: 4 Ill.
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Viscosity and preferential solvation measurements were carried out on ionized maleic acidethyl, -butyl, and -hexyl vinyl ether alternating copolymers (i-MA/EVE, i-MA/BVE, and i-MA/HVE, respectively) in water-2-chloroethanol mixtures. i-MA/EVE and i-MA/BVE are completely coiled and their preferential and absolute solvation by water and 2-chloroethanol reflects their more or less hydrophilic or hydrophobic nature. For i-MA/HVE, the viscosimetric and preferential solvation measurements suggest that, in 2-chloroethanol rich mixtures, the polymer retains a hypercoiled conformation in which an important part of the hexyl side chains are screened form contact with both componenets of the solvent mixture.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 2091-2104 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quasielastic light scattering is used to study the effect of ionic strength on the dynamic behaviour of DNA. In a first approach the spectrum of scattered light is analyzed in terms of a single relaxation process. The large difference between the observed behaviour and that expected according to a pure diffusional process reflects the contribution associated with internal modes, which increases with decreasing ionic strength. Such behaviour is better analyzed in terms of a double relaxation process by using two relaxation times, the reciprocals of which are equal to DK2 and DK2 + τi-1 (K), respectively, where τi (K) is an average value describing the set of modes observed at a given K value. Relative intensity and relaxation times, which are the more accurate parameters, were used to interpret the results. The observed increase of the relative contribution of internal modes with decreasing ionic strength is actually a relative decrease of the diffusional contribution induced by a corresponding increase of the radius of gyration RG. On the other hand, the reciprocal τi-1 (K) of the relaxation time is a linear function of K2 in the analyzed KRG range and is insensitive to ionic strength between 10-2M and 1M. These results, when discussed according to Rouse's model, lead to define for each value of τi-1 (K) a corresponding mean-squared equilibrium length 〈μi2〉 which is found to be a linear function of K-2.
    Additional Material: 9 Ill.
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  • 8
    ISSN: 0006-3525
    Keywords: ACTH ; lipid-peptide interaction ; 1H-nmr ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of the 5-14, 1-14, and 1-24 fragments of ACTH with sonicated phospholipid bilayers containing egg yolk phosphatidylcholine (EPC) either pure or mixed with 10 mole % phosphatidic acid (EPA), was investigated by proton nuclear magnetic resonance (1H-nmr). The effects observed with zwitterionic EPC vesicles were small, indicating a low binding of the ACTH derivatives. The N-terminal aromatic resonances of the ACTH peptides were markedly broadened in the presence of negatively charged vesicles (EPC/EPA 9:1 M/M), while those of the C-terminal end were barely affected, showing that ACTH interacts with its N-terminal fragment. The choline resonance of the EPC molecules of the outer monolayer was shifted and broadened upon ACTH binding to the lipid vesicles, while that of the inner layer was not affected, suggesting that the peptide molecules interact only with the external leaflet of the lipid bilayer. The C2H and C4H resonances of the histidine-6 side chain were both shifted downfield upon peptide binding to the negatively charged lipid interface. In the case of the 1-24 derivative, these resonances were also split into two signals reflecting two different species of membrane-bound ACTH 1-24. Analysis of the line width and chemical shift variations of the ACTH and lipid resonances observed upon peptide binding shows that the membrane-binding potency of the shorter 5-14+1 fragment, which presents a +1 net charge, is roughly similar to that of the highly cationic 1-24+6 (net charge +6) derivative, implying that the 15-24+5 segment is not essential for membrane binding. The nmr measurements at a fixed lipid-to-peptide ratio in the presence of increasing amounts of spin-labeled lipids demonstrate that the N-terminal fragment of ACTH does not penetrate the hydrophobic core of the bilayer, and should lie parallel to the membrane surface. © 1997 John Wiley & Sons, Inc. Biopoly 42: 731-744, 1997
    Additional Material: 11 Ill.
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  • 9
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleophilic substitution of the chlorine atoms of poly(vinyl chloride) with sodium thiophenate is assumed to obey an SN2 mechanism with inversion of configuration and a steric control according to which reactivities R of the triads follow the order Rmm 〉 Rmr ≫ Rrr. Such a reaction cannot be described by simple differential equations, but a Monte Carlo simulation, first generating a random Bernouillian chain and then simulating random attack of the chain by the reactant according to the triad reactivities, allows a good agreement with the experimental results of both the kinetics of a reaction carried out in cyclohexanone solution at 40°C and the evolution of the 13C and 1H NMR spectra of the tertiary carbon atoms, assuming the following parameters: Bernouillian probability for a meso placement in the initial chain: 0.431; relative reactivities of the mm, mr and rm, rr triads: 1, 0.5, and 0., respectively. The agreement is excellent until the reaction is about three-quarters complete; this shows a limiting level of about 60% substitution. Better agreement can be obtained up to the limit, if a secondary process of steric control by the substituant in a partially substituted mr triad is assumed. Other possibilities for that secondary process are discussed.
    Additional Material: 21 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An amorphous monomeric glass is defined as a mixture of compatible organic monomeric molecules with an infinitely low crystallization rate under the most favorable conditions. These mixtures can be formed in a one-part reaction of a multifunctional nucleus with a mixture of substituents. The “noncrystallizability” of the mixture is controlled by the structural dissymmetry of the nucleus and/or the substituents and the number of components making up the mixture. We have developed an equation to calculate the number of components in a given mixture, knowing the structure and functionality of the nucleus and the number of substituents. An HPLC characterization method was developed and used to investigate the effects of various reaction conditions on the component concentration distributions and physical properties of the resulting materials. A dissymmetry number defined as the total weight percent of odd-substituted components is believed to be a potential measure of the “noncrystallizability” of the mixture. Physical properties such as glass-transition temperature can be dramatically increased through controlled oligomerization at the price of a moderate increase in melt viscosity. The organic monomeric glasses, like amorphous polymers, have good film-forming properties. However, unlike polymers, they display extremely low melt-viscosities and large positive entropy-of-mixing values and can be ground easily into extremely small particles. These properties make them ideal for certain applications where compatibility, melt-flow, and small particle size are important.
    Additional Material: 10 Ill.
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