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  • 1
    Electronic Resource
    Electronic Resource
    A solid-state 13C-NMR study of crosslinking in polybutadiene by γ radiation: Effect of microstructure and dose (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 185-195 
    Details
    ISSN: 0887-624X
    Keywords: radiation ; polybutadiene ; crosslinking ; solid-state NMR ; 13C-NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solid-state 13C NMR spectroscopy has been used to determine the decrease in C=C bonds, formation of crosslinks and cis to trans isomerization during the γ irradiation of (a) 〉 99% cis, 1,4-polybutadiene, (b) 54% trans, 41% cis, 1,4-polybutadiene, and (c) 86% 1,2-polybutadiene. G(-cis C=C) and G(-trans C=C), were similar and decreased with dose from ≈ 40 for 0-1 MGy to 5 for 5-10 MGy. G(-double bonds) and G(crosslink) were comparable, indicating that crosslinking occurred through the double bonds. G(crosslink) was much higher than values derived from physical properties, confirming that NMR measures the total of inter- and intramolecular crosslinking (cyclization). The 1,2 polybutadiene was much more sensitive to crosslinking, and a value of G(-C=C) = 240 was obtained at low doses. Crosslinking evidently proceeds by a kinetic chain reaction in all three types of polybutadiene.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300202
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanism of radiation degradation of polyisobutylene (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 971-984 
    Details
    ISSN: 0887-624X
    Keywords: radiation ; polyisobutylene ; NMR ; GC/MS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GC, GC/MS, GPC, and Solution NMR spectra were used to study the γ radiolysis of polyisobutylene (PIB) in vacuum to different total doses (0-900 kGy) and at different temperatures (77-423 K). NMR spectra show a large number of new resonances with relatively narrow line widths, and a variety of NMR techniques have been employed to determine and quantify the structures associated with these new resonances. Chemical shift assignments were made by comparison with those for small molecule model compounds and predictions based upon calculations according to several different schemes. Chain-end structures have been proposed that account well for the majority of the new resonances, all being the result of an initial chain scission reaction initiated by the radiation. These assignments support some previous proposals for the mechanism of radiation degradation of polyisobutylene and exclude others. For example, NMR provides no evidence for the formation of ethyl chain ends and some of the main chain unsaturated structures previously proposed. NMR also indicate that at higher doses the chain end products formed during initial stages undergo secondary reactions. GC/MS data show the formation of oligomers during irradiation, which may be due to a backbitting mechanism. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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