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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Mutation Research Letters 281 (1992), S. 169-171 
    ISSN: 0165-7992
    Keywords: Cocoa, irradiated ; Drosophila melanogaster ; Irradiated cocoa ; LD values ; Wing spot test
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 183 (1982), S. 2555-2563 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(pentamethylene sulfide)Structure-based name: poly(thiopentamethylene). (P5MS) [—S(CH2)5—]x was prepared by the condensation polymerization of nearly equimolar amounts of pentamethylene dibromide and the sodium salt of 1,5-pentanedithiol. Selective precipitations were used to obtain a fraction of the polymer, and dielectric constant measurements on solutions of it in benzene were used to obtain dipole moments over the range 20-60°C. Rotational isomeric state calculations based on conformational energies obtained from semiempirical potential energy functions gave results in fair agreement with experiment. Since extensive previous studies on a number of polyoxides have demonstrated the difficulty in calculating the energy of the O…CH2 interactions, the energy of the corresponding S…CH2 interactions in P5MS was adjusted to obtain better agreement between theory and experiment.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 183 (1982), S. 2565-2572 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Several earlier studies of poly(alkylene sulfides) have not yielded evidence for a sulfur gauche effect, in contrast to the large attractive gauche effect found particularly in the lower members of the poly(alkylene oxides). In this study the dipole moments at 25°C and the corresponding temperature coefficient of poly(1,3-dithiocane)Structure based name: poly(thiomethylonethiopentamethylene). [—SCH2S(CH2)5—]x are calculated in the rotational isomeric-state approximation, and the results compared to the values determined by experiment. In the calculations the energy Eσ′ = [Eg± - Et] associated with S. . .CH2 interactions in the SCH2—SCH2 segment is adjusted to attain agreement between theory and experiment. The results indicate that an extra stabilization energy of ca. 0,9 kcal . mol-1 must be added to these gauche states relative to the trans state (beyond that determined by conformational energy calculations based on semiempirical potential energy functions). This provides the first evidence of a large attractive sulfur gauche effect in the polysulfides, about equal in magnitude to that found for the analogous poly(methylene oxide).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Conformational energy calculations indicate that poly(trimethylene sulfide) (P3MS) approximates the idealized freely-rotating chain in that gauche-trans energy differences in this molecule are very small. This occurs because the relatively long S—C bond tends to relieve congestion within the P3MS chain. The bonds in poly(trimethylene oxide) (P3MO) are much more constrained to a particular rotational state because the O—C bond is shorter than the S—C one, and in this sense P3MO is considerably less flexible. In this study the dipole moments 〈μ2〉0 of P3MS are measured as a function of temperature, and the results analyzed in terms of the rotational isomeric-state theory. Using conformational energies derived from semiempirical potential energy functions, a three-rotational-state model gave values of the dipole moment in good agreement with experiment. Theoretical and experimental values of the temperature coefficient of 〈μ2〉0 were in disagreement, however, and a five-rotational-state model based on that adopted by Flory in a similar study of polymethylene failed to remove this discrepancy. Some statistical properties are tabulated for the n-alkylene polysulfides studied to date and for structurally related polyoxides. In these types of molecules, strong preferences for pairs of gauche states in CH2S—CH2—SCH2 and CH2 O—CH2—OCH2 sequences give rise to unusually small values of the dipole moment.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2565-2576 
    ISSN: 0887-624X
    Keywords: acrylate monomers ; polymerization kinetics ; stereostructure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of new unsaturated monomers containing functional groups has been theoretically analyzed by considering a simple kinetic scheme. In the reactions between acetyl and acryloyl chloride with neopentylglycol, it was shown that the comparison between theoretical and experimental results, does not allow us to conclude that the two rate constants controlling the reactions are equivalent. Kinetic experiments of the polymerization of 3-hydroxyneopentyl acrylate were carried out in benzene and 1,4-dioxane solution at different temperatures. Dilatometric techniques and nonlinear least-squares methods were used to obtain kinetic data and to determine the kinetic constants, respectively. The values of \documentclass{article}\pagestyle{empty}\begin{document}$k_p /k_t^{1/2}$\end{document} for this monomer were found higher in dioxane than in benzene due, probably, to the fact that in the last solvent the polymerization is heterogeneous. The activation energy, determined by using different values of \documentclass{article}\pagestyle{empty}\begin{document}$k_p /k_t^{1/2}$\end{document} was found 7.6 kcal/mol. The stereostructure of the polymers derived from 3-hydroxyneopentyl acrylate and 3-acetoxyneopentyl acrylate was determined by 13C-NMR spectroscopy from the analysis of the resonance signals belonging to the carbonyl groups, obtaining values for the fraction of isotactic dyads in the range 0.36 ± 0.03 for both polymers. Finally, the glass transition temperatures of both polymers, determined calorimetrically, were found 281 and 255 K, respectively. © 1994 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 1045-1051 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of thermal initiation of the radical polymerization of unsaturated monomers has been analyzed by considering a kinetic scheme that includes thermal- and catalyst-induced formation of free radicals, propagation, and termination reactions. Expressions relating the different rate constants with the instantaneous monomer concentration are derived and they indicate the great influence of thermal initiation on the kinetic results. Application to a real case suggests that evaluation of kd and kp/kt1/2 from experimental results using the method of dead-end polymerization may lead to erroneous values of these constants.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0887-624X
    Keywords: postpolymerization reactions ; ESR ; polymeric matrices termination reactions ; H-transfer reactions ; kinetic constants ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction kinetics in the dark of photopolymerized mono- and dimethacrylates in a polymeric binder has been studied. Electron spin resonance spectroscopy (ESR) provided useful information regarding the nature of the radicals involved in postpolymerization reactions. Computer simulations were performed to study the decay of the propagating radicals by considering normal bimolecular termination and transfer reactions of the radicals to the binder. Differences were found in the termination reactions for mono- and difunctional monomers when they were photopolymerized in a solid medium. Absolute kinetic constants for H-transfer reaction with the binder, relative kinetic rate constants for radical-radical coupling, and average lifetimes for the radicals have been calculated. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2785-2791, 1998
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 2057-2067 
    ISSN: 0887-624X
    Keywords: methacrylate monomers ; polymerization kinetics ; stereostructure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of unsaturated monomers containing one or more hydroxyl groups by reaction between polyalcohols (number of OH, n≥2) and monoacid chlorides has been theoretically analyzed. The difficulties were shown involved in the preparation of these monomers with a high degree of purity even in the most favorable case of the completely substituted compound. The calculated mole fractions of the two monomers that can be obtained by reaction between neopentylglycol and methacryloyl chloride were compared with the experimental ones. Kinetic experiments of the polymerization of 3-hydroxyneopentyl methacrylate and 2-hydroxyethyl methacrylate were carried out at different temperatures in 1,4-dioxane for the former monomer and dioxane and absolute ethanol for the latter. Dilatometric techniques and nonlinear least-squares methods were used to obtain kinetic data and to determine the kinetic constants, respectively. In homogeneous solution the values of kp/k1/2t for the 3-hydroxyneopentyl methacrylate and 2-hydroxyethyl methacrylate was determined by 13C-NMR spectroscopy and the molar fractions of tactic triads and dyads were calculated from different resonance signals. The polymers are predominantly syndiotactic and follow a Bernoullian distribution of tactic sequences. Finally, the glass transition temperatures of both polymers, determined calorimetrically, were 145 and 89°C, respectively. © 1995 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 365-371 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bulk cationic copolymerization of tetrahydrofuran and 3-methyl-tetrahydrofuran was studied at 0°C with acetylhexafluoroantimonate as initiator. The experimental equilibrium concentrations of both monomers were determined in all the intervals of composition, and the results obtained were compared with those calculated by different methods developed to study copolymerization systems in which depropagation reactions play an important role. In particular, very good agreement between calculated and experimental values was obtained by using Monte Carlo methods of simulation that allow the determination of the unknown cross-propagation and cross-depropagation rate constants, a necessary condition to calculate the equilibrium monomer concentrations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 24 (1986), S. 337-344 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dynamic mechanical experiments were performed between -140 and 50°C on both poly(diethylene glycol isophthalate) and poly(triethylene glycol terephthalate) networks. Plots of loss tangent versus temperature show a well-defined α peak, associated with the transition from glasslike to rubberlike consistency, and two overlapping peaks (β1 and β2) in the glassy region. Dynamic deformations of small amplitude were superimposed on large static deformations. It was found that the position of the β1 and β2 peaks as well as their intensities are independent of the static elongation ratio. However, the intensity of the loss tangent associated with the glass-rubber transition tends to decrease with increasing static deformation. Moreover, the position of the maximum of the α peaks shifts to lower temperatures as the elongation ratio increases. This behavior suggests that for both networks the volume effects (shifting the α peaks to lower temperatures with increasing elongation ratio) overcome the entropic effects (shifting the α peaks to higher temperatures with decreasing entropy).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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