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  • 1
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The glass transition temperature of copolymers of methacrylonitrile with methyl, ethyl and butyl esters of methacrylic acid, together with those of the corresponding homopolymers, were determined by differential scanning calorimetry. The variation of the glass transition temperature (Tg) of copolymers with the composition of the samples was analyzed for each system on the basis of treatments suggested by Barton, Johnston and Suzuki-Mathot, determining the values of the glass transition temperature of the alternating diad (Tg12). It was observed in all the cases that the alternating diad presents a flexibility higher than that expected from the combination of both kinds of monomeric units according to the Tg of the corresponding homopolymers and that the Tg12 values decrease with the length of the side chain of the methacrylate ester in the system, as the Tg values of the polymethacrylates.
    Additional Material: 8 Ill.
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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: The heterogeneous hydrolytical behaviour of hydrogels based on copolymers of 2-hydroxyethyl methacrylate (HEMA) with 4-(methacryloyloxy)acetanilide (MOA)b is analyzed by measuring the concentration of active metabolites released into the alkaline-buffered solution used as the hydrolytical medium. Previously, we studied the swelling of hydrogel matrices of copolymers prepared with a MOA content between 1,0 and 5,0 wt.-%, in order to know the diffusional character of the reagents and the released species. The results obtained demonstrate that the swelling phenomenon is much faster than the hydrolytical chemical reaction. Thus, the hydrolysis is studied on the basis of a kinetic scheme which considers the formation of different kinds of residues, i.e., the sodium salts of 4-hydroxyacetanilide (PC) and 4-aminophenol (PA), according to the UV spectra obtained at different times of treatment. The characteristic rate coefficients, k1, k2, kc and k′c are evaluated from the experimental data on the basis of the suggested kinetic scheme.
    Additional Material: 5 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 625-631 
    ISSN: 0887-624X
    Keywords: copolymers ; furfuryl acrylate ; hydroxyethyl methacrylate ; biomaterials ; glass transition temperature ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copolymers of furfuryl acrylate (F) and 2-hydroxyethyl methacrylate (H) were prepared by free radical polymerization in DMF solution at 50°C, using 2,2′-azobisisobutyronitrile (AIBN) as initiator. The reactivity ratios of both monomers were calculated according to the general copolymerization equation using the Fineman-Ross and Kelen-Tüdös linearization methods, as well as the Tidwell and Mortimer nonlinear least-squares treatment. The reactivity ratios obtained were rF = 0.93 and rH = 1.42. The microstructure of copolymer chains is described on the basis of first-order Markov statistics, and the copolymer glass transition temperatures were determined calorimetrically. The variation of Tg with the copolymer composition is discussed according to modern methods, considering the sequence distribution of monomeric units along the copolymer chains. Also the Tg of the corresponding homopolymers was determined giving the values Tg(F) = 321 K and Tg(H) = 358 K, whereas the Tg of the corresponding alternating diad has an average value of TgFH = 326 K. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 4
    ISSN: 0935-9648
    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
    Additional Material: 8 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 711-717 
    ISSN: 0887-6266
    Keywords: poly(cyclohexyl acrylate), relation between mechanical and dielectric relaxations in ; relaxations, mechanical and dielectric, in poly(cyclohexyl acrylate) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Storage E′ and loss E″ relaxation moduli are reported as functions of frequency for poly(cyclohexyl acrylate) (PCA) at several temperatures. The possibility that these results, in conjunction with the dipolar correlation coefficient, can be used to predict the frequency dependence of the real ε and loss ε″ and the components of the complex dielectric permittivity ε* of PCA is studied. A relation between ε* and the complex relaxation modulus E* is obtained by assuming that the lag of the rotating dipoles in the electric field is caused by both dielectric and mechanical friction. The values of ε* obtained from mechanical results by means of this expression are very close to those obtained from other relations based on the assumption that the lag of the dipoles is caused exclusively by mechanical friction. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 485-493 
    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 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.
    Additional Material: 8 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 1239-1246 
    ISSN: 0887-6266
    Keywords: poly(cyclohexyl acrylate), activation energy for β relaxations of ; mechanical and dielectric β relaxations of poly(cyclohexyl acrylate) ; activation energy of β relaxations of poly(cyclohexyl acrylate) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interpretation of the mechanical and dielectric β relaxations of poly(cyclohexyl acrylate) by the coupling scheme suggests that the dielectric relaxation process is more complex than the mechanical one, contrary to what occurs in the glass-rubber relaxation. The distribution of activation energies for the dielectric process, obtained from isochronal and isothermal loss curves, increases with temperature and frequencies. The determination of the distribution of the activation-free energy indicates a distribution of the activation entropy for both the mechanical and dielectric β process, suggesting that a distribution of preexponential factors in the Arrhenius equation also exists. © 1992 John Wiley & Sons, Inc.
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  • 8
    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 thermal behaviour of random copolymers of furfuryl methacrylate (F) and N-vinylpyrrolidone (P) was studied by means of dynamic thermogravimetric analysis (TGA) in the range 100-600°C. The dynamic experiments show that these copolymers exhibit two degradation steps in the intervals 260-320°C and 350-520°C, respectively. The normalized weight loss in the low temperature interval increases as the mole fraction of F in the copolymer mF increases, whereas an inverted trend in the high temperature interval is observed. The apparent activation energy Ea of the first degradation step for copolymers prepared with different composition, was obtained according to the treatment suggested by Broido. A plot of the values of Ea versus the F diad molar fraction in the copolymer chains mFF gave a straight line that indicates that there is a direct relationship between the thermogravimetric behaviour of these systems and their corresponding microstructure, that is, the distribution of comonomeric units along the copolymers chains. The first decomposition step was also studied by isothermal TGA and a good linearity for the variation of the weight loss percentage ΔW versus mF at least during the first 30 min of treatment was obtained. These results also indicate that from a kinetic point of view the isothermal degradation in these conditions follows a first order behaviour and the corresponding reaction rate constants increase linearly with mFF. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 54 (1994), S. 959-968 
    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: Hydrogels of biomedical interest were prepared by the free redical copolymerization of 2-hydroxyethylmethacrylate, H, with furfuryl acrylate, A, at low and high conversion. The microstructural analysis of the copolymer system was carried out by nuclear magnetic resonance (NMR) spectroscopy, taking into consideration statistical perameters according to the Mayo-Lewis copolymerization model. The hydration process in physsiological conditions was studied gravimetrically at 37°C, following the kinetics of swelling of homogeneous thin films. A diffusion mechanism based on the stress relaxation model of copolymer chains accounts satisfactorily for the expermental data obtained. The diffusion coefficents determined according to the classical to the Fickian uptake kinetics are very sensitive to the copolymer's composition. © 1994 John Wiley & Sons, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 12 (1991), S. 319-323 
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 3 Ill.
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