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  • 1
    Electronic Resource
    Electronic Resource
    Ionic species in irradiated poly(methyl methacrylate). A pulse radiolysis and ESR study (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 3257-3268 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(methyl methacrylate) free of initiators was synthesized by γ-irradiation and cast into transparent films. The samples were investigated by ns pulse radiolysis at various temperatures, and by ESR spectroscopy after γ irradiation at 77°K. Short-lived transients with optical absorptions at 440 and 725 nm were observed. The 440 nm absorption has been ascribed to the cation and the 725 nm absorption (εG = 3000 M-1 cm-1 (100 eV)-1, τ1/2 = 190 ns at -13°C, Ea = 6.5 kcal/mol) to the anion. These assignments are based on ESR data of samples of poly(methyl methacrylate) and pivalic acid methyl ester deuterated at the ester deuterated at the ester and α-methyl groups, respectively, and subjected to thermal annealing and photobleaching. The anion decomposes on photobleaching by loss of the ester ·CH3 radical, and the cation is proposed to decay by loss of the ·CH3 radical from the α-methyl group. The thermal decay of the anion is discussed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1983.170211122
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  • 2
    Electronic Resource
    Electronic Resource
    Cationic and polymeric radicals of vinyl monomers in halogenated matrices: An ESR and SCF MO study (1988)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 26 (1988), S. 2725-2736 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vinyl monomers methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, and β-methylstyrene were dissolved in CF3CCl3, x-irradiated at 4 or 77 K, and investigated by ESR spectroscopy. The molecular cation of methyl acrylate has no resolved hyperfine structure, indicating that the unpaired electron is localized on the carbonyl oxygen. Evidence that a two-stage photoinduced reaction gives rise to a propagating radical was obtained. Propagating radicals were observed also with methyl methacrylate, acrylic acid, and methacrylic acid as solutes. The positive ion of β-methylstyrene has been prepared and characterized. The experimental data have been compared with molecular orbital calculations at different levels of approximation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1988.080261009
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    ESR single-crystal study of radical and radical-pair formation in some γ-irradiated vinyl monomers (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 9 (1971), S. 1495-1507 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Single crystals of methyl methacrylate (MMA), methyl acrylate (MA), and acrolein (A) have been prepared by a low-temperature technique. After irradiation with γ-rays at 77°K the paramagnetic species were identified by ESR spectroscopy. MMA gave a seven-line single spectrum from radicals formed by hydrogen addition. The hyperfine coupling constants are slightly anisotropic with a mean value of 22 G. Radical pairs were observed as ΔMs = 1 and ΔMs = 2 transitions; the hyperfine coupling was 11 G. From the strongly anisotropic dipolar interaction, upper limits for the distances between the pair components were calculated to be 5.45 Å and 6.3 Å. MA gave a five-line main spectrum with the same hyperfine coupling values and two radical pairs, one with a distance 5.9 Å between the components. In a there was also a strongly anisotropic interaction. The hyperfine coupling of the ΔMs = 2 transition was 9.8 G. The number of radical pairs compared to the total number of radicals increases only slightly with the radiation dose. This makes it likely that pair formation occurs in the spurs and blobs formed by the γ-radiation. At an increased temperature the radical pairs disappeared; the spectrum of MMA changed to that characteristic of propagating polymer radicals.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.160090809
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    Paper (German National Licenses)
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