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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 1364-1369 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    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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  • 3
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic substitution of PVC with sodium thiophenate was carried out in cyclohexanone solution at 5, 25, 40, 60, and 70°C. The initial rate obeys an Arrhenius law from 25 to 60°C, with an activation energy of 70 kJ/mol. Conversion limits are observed which strongly depend on the temperature. The stereoselectivity of the reaction with respect to the configurational triads does not depend on the temperature: the distribution of configurations is only dependent on the conversion. Assuming an SN2 substitution mechanism governed by steric factors, the Monte Carlo simulation procedure described in a prior study is shown to give a good account for all temperatures above 40°C assuming for the mm, mr or rm, and rr triads a reactivity such as Rmm = 2 Rmr and Rrr nil at low temperature and very low at temperatures ≥ 40°C. The low conversion limits observed at 5 and 25°C cannot be explained by a limited accessibility of a part of the polymer. Finally, it is shown that the elimination reaction, which remains limited, does not interfere with the substitution process.
    Additional Material: 8 Ill.
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  • 4
    ISSN: 0887-624X
    Keywords: Polyvinylchloride ; vinylchloride-vinylthiocresol copolymer ; vinylchloride-vinylthionaphthol copolymer ; vinylchloride-vinylthiobenzene copolymer ; glass transition temperature ; NMR spectroscopy ; polymer-solvent interaction ; polymer association ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vinylchloride-vinylthiocresol and vinylchloride-vinylthionaphthol copolymers of various compositions were prepared by the substitution reaction of PVC with sodium thiocresol and sodium thionaphthol, respectively, in different solvents and at different temperatures. The variation of the glass transition temperature of these copolymers with chemical com-position does not follow the Flory-Fox equation, but is found to depend on the solvent and the temperature at which the copolymer is obtained. The comonomer sequence distribution and stereosequence content of the above copolymers, and those of vinylchloride-vinyl-thiobenzene copolymer, were determined by 1H- and 13C-NMR spectroscopy. The depen-dence of comonomer distribution and stereoregularity content with chemical composition for the three series of copolymers, prepared in different solvents and temperatures, are similar. The Tg deviations for the three series of copolymers were attributed to the con-tribution of physical characteristics of the PVC structure, originating from polymer-solvent interactions. © 1995 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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  • 5
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature dependences of the associated fraction of PVC units were determined from measurements of integrated intensities of high-resolution 1H NMR spectra in thermoreversible gels of PVC and chemically modified PVC in diethyl oxalate (DEO) and dibutyl oxalate (DBO). The existence of two types of associates of different thermal stability, completely melting at 55°C and 90-130°C, was indicated by these measurements. While the associated fraction and the thermal stability of the associates increase with increasing polymer concentration, a significant reduction in the associated fraction is observed in samples where ≈5% of chlorine atoms are replaced by phenylthio groups or hydrogen. Because the chemical modification takes places only on isotactic and heterotactic triads, this result confirms the important role of these sequences in interactions associated with the gel formation. In DBO gels, the values of the associated fraction are lower than in DEO gels. A complete parallelism was found for temperature dependences of the associated fraction and viscoelastic storage modulus. From measurements of selective and nonselective 1H spin-lattice relaxation times of the solvent, the existence of PVC/DEO complex was confirmed. The life-time of bound solvent molecules which could bridge different chains is shorter than 1 s. Both polymer/solvent complex and polymer-polymer interactions seem to act as physical crosslinks.
    Additional Material: 7 Ill.
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  • 6
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The modification of PVC with 4-mercaptopyridine is described. The content of pyridine groups in the products is measured by NMR and IR spectroscopy. The degree of modification depends on the reaction conditions, and values of up to 70% are achieved without degradation or other appreciable side reactions. The tertiary amino groups in the polymer can be alkylated with iodides of varying chain length to form quantitatively quaternary pyridinium salt groups, leading to PVC ionomers and polyelectrolytes.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 15-23 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2-Mercaptobenzyl alcohol and 4-mercaptobenzyl alcohol were synthesized in good yields starting form thiosalicylic acid and p-toluenesulfonic acid, respectively. Poly(vinyl chloride) (PVC) reacts selectively with the thiol group of these bifunctional compounds leading to modified PVC with free hydroxy groups. In a second step the polymer chains can be partially crosslinked by reaction with hexamethylene diisocyanate. According to the degree of PVC modification, the network density of the resulting elastomers is freely adjustable.
    Additional Material: 5 Ill.
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  • 8
    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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  • 9
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acetone-soluble and -insoluble fractions were obtained from two different PVC samples: a polymer prepared in our laboratory at 60°C using 2,2′-azoisobutyronitrile (AIBN) as initiator (sample A) and a commercial polymer prepared at 70°C (sample B). The content of isotactic, syndiotactic and heterotactic traids was accurately measured by high resolution 13C NMR. From the obtained data it follows that the isotactic triads accumulate preferably in the soluble fraction, the amount of which depends on the type of polymer. In agreement with earlier results, the soluble fraction is about 40% less stable than the insoluble fraction. The reasons for this behaviour are discussed in the light of the higher content of both isotactic triads and some defect structures, as found in the low molecular weight soluble extracts of PVC.
    Additional Material: 1 Ill.
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  • 10
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The substitution reaction of PVC with sodium dimethyldithiocarbamate (NaDC) and sodium azide (NaN3) was performed in cyclohexanone and dimethylformamide at various temperatures. The degree of compositional heterogeneity was estimated and found to be important up to conversions of about 0,5%, but to vanish afterwards. The evolution of unreacted iso, hetero and syndiotactic triads was measured by 13C NMR spectroscopy. For conversions of at least up to 12%, the content of both the isotactic and heterotactic triads was found to decrease, relative to the syndiotactic ones, but at different relative rates depending on the nucleophile. From these results, together with the kinetic ones, it is concluded that the reaction proceeds by a stereoselective mechanism. The results are discussed on the basis of a hypothesis concerning the role of the local triad conformations in PVC that contain the TT isotactic diad conformation. The results enable the selective substitution of PVC with NaDC and NaN3, which may be used as a useful tool to prepare specific graft copolymers based on PVC.
    Additional Material: 5 Ill.
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