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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 15 (1977), S. 2919-2933 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A sample of polystyrene with narrow molecular weight distribution (M̄w/M̄n = 1.03) has been formed into a 3-mm sheet and subjected to γ-irradiation at 25°C in air. Simultaneous crosslinking and scission of polymer chains resulted. Analyses by velocity and equilibrium sedimentation, gelpermeation chromatography, and osmometry of the polystyrene subjected to doses in the range 0-90 Mrad, all within the pre-gel region, have yielded average values of G(S) = G(X) = 0.022 ± 0.002 for the complete sample. Combination of these various experimental techniques has been successful in yielding consistent values of G(S) and G(X) and should be applicable with advantage to other polymers, particularly when neither G(S) nor G(X) is zero. The wide variation in literature values of G(S) and G(X) for irradiation of polystyrene under vacuum precludes any unequivocal conclusion on the effect of air on the radiation yields.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 20 (1982), S. 241-244 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simplified approximation method for the treatment of dead-end and high conversion polymerization kinetics is presented. The method is based on the treatment of dead-end polymerization first described by Tobolsky. In appropriate circumstances, by contrast with Tobolsky's method, this method provides measurements of kd and kp/kt1/2 without recourse to the measurement of the monomer conversion at infinite time.Kinetic studies of free radical polymerizations are normally confined to measurements of initial rates. At low conversions the predictions of the general mechanism for chain-growth polymerization involving initiation, propagation, and termination steps are generally obeyed. Thus the polymerization rate should be first order in the vinyl monomer and half-order in the initiator concentrations.At high conversions, however, large deviations which can be ascribed to various effects can occur; for example, (1) the effect of the increasing viscosity of the polymerization medium on the termination rate constant kt, and possibly also on the propagation rate constant kp, which have been considered by North1 and Cardenas and O'Driscoll,2 or (2) depletion of the initiator as the polymerization progresses. This depletion will occur in all polymerizations but its significance will depend on the magnitude of the rate constant for initiator decomposition (kd) and the period of polymerization. Appropriate conditions will lead to limiting monomer conversion even after infinite polymerization time; this phenomenon has been called dead-end polymerization by Tobolsky.3Free radical polymerizations to high conversion are particularly important in the industrial context when initial kinetics are obviously inadequate. Suitable treatment of the conversion/time relationship is highly desirable.Senogles and Woolf4 have examined the polymerization of n-lauryl methacrylate at 60°C with 2-azobisisobutyronitrile as initiator under dead-end conditions.Here we propose a modification of Tobolsky's treatment of such polymerizations by using an approximation for the exponential decay in the initiator concentration. This method permits easy manipulation of the experimental data and the estimation of values for the kinetic parameters in favorable circumstances without recourse to the measurement of the conversion at infinite time or the evaluation of complicated functions of the monomer conversion. The method thus allows the duration of the laboratory experimentation to be significantly shortened and the complexity of the subsequent data analysis to be considerably reduced.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 15 (1977), S. 131-139 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of γ-irradiation on poly(tert-butyl crotonate) has been investigated by velocity sedimentation and solubility studies. Evidence of significant crosslinking as well as of chain scission has been obtained, the estimates of G(X) and G(S) being 0.66 and 0.59, respectively.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 17 (1979), S. 4081-4088 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements of molecular weight averages and distributions have been made on three samples of narrow molecular size distribution polystyrene with molecular weights from 100, 000 to 400, 000 subjected to 60Co γ irradiation in vacuo for various doses within the pregel region+ G(X), the radiation chemical yield of crosslinking, has been determined as 0.043 ± 0.002 and G(S)/G(X), the ratio of scission to crosslinking, as 0.02; no effect of molecular weight was observed. By comparison with previous experimental results for polystyrene irradiated in air it has been established unequivocally that an oxygen environment leads to enhanced scission at the expense of crosslinking. Literature values of G(X) and G(S)/G(X) are reviewed in the light of these results and explanations are offered to account for major discrepancies.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 16 (1978), S. 1515-1518 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 6 (1968), S. 1073-1086 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The postirradiation polymerization of the crystalline, anhydrous, monohydrate, and dihydrate forms of zinc methacrylate was studied. The anhydrous salt polymerized readily in the temperature range 50-150°C., the monohydrate did not polymerize at all, and the dihydrate polymerized at about 100°C. Aging of the anhydrous salts greatly affected the rate of polymerization; this was shown to be due mainly to the formation of peroxides by reaction with air. Polymerization could be initiated thermally, without irradiation, in monomer which had been aged in contact with air, apparently by decomposition of the peroxides. The rate of the postirradiation polymerization was increased when air was present during irradiation and decreased when air was present during polymerization. The rate of polymerization increased with temperature, corresponding to an apparent activation energy of 10 kcal./mole. The dihydrate lost one molecule of water rapidly under vacuum at 20°C. and slowly on heating at 50°C. in a sealed vessel, forming a crystalline monohydrate. Slow thermal polymerization and rapid postirradiation polymerization occurred at 100°C. without the formation of any monohydrate, indicating that the polymerization was concurrent with the phase change.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 1997-2004 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixtures of sulphur dioxide and butene-1 have been polymerized in the gas phase to the 1:1 alternating copolymer by electron irradiation. The rate of polymerization, measured by the decrease in gas pressure, decreased with increase in temperature over the range -20 to +30°C. The initial G(-monomer) values decreased from 500 to 50 giving an Arrhenius activation energy of -30 kJ mol-1. These results are consistent with a ceiling temperature-pressure relationship. The ceiling temperature is about 60°C lower than that observed previously in the liquid phase in accord with thermo-dynamic prediction.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 7 (1969), S. 1657-1664 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Octadecyl methacrylate (mpc ≈ 12°C.) polymerized readily in the solid state in the temperature range -30 to +12°C. after gamma irradiation at -196°C. The initial rate of polymerization and the “limiting” conversion increased with radiation dose and temperature. The temperature dependence of the rate corresponded to an “apparent” activation energy of 20 kcal./mole. Difficulties were experienced with polymerization during separation of the polymer from residual monomer, but these were minimized by using low radiation doses and a hot, selective solvent. The maximum conversion achieved was 70%. The polymer was crosslinked, even at low conversions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 7 (1969), S. 1665-1674 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron spin resonance spectrum of gamma-irradiated octadecyl methacrylate (m.p. ≈ 12°C.) was due to a mixture of three radicals formed by (1) loss of a hydrogen atom from the paraffin chain, (2) addition of a hydrogen atom to the double bond, and (3) addition of a monomer molecule to radicals formed by (1) or (2). On warming monomer added to radicals (1) and (2) between -170 and -50°C., and above -50°C. the spectrum was solely due to propagating methacrylate radicals. The total radical concentration decreased slightly at -150°C. and was then constant up to -30°C. A marked decrease in radical concentration occurred from -30 to +12°C., it took place rapidly and reached an equilibrium value after each successive increase in temperature. Differential thermal analysis indicated a solid - solid phase change at -30°C. When the sample was kept at 0°C. there was no further decrease in radical concentration even with 50% conversion to polymer. With 2% added chloranil the (chloranil)- was observed to be of about the same concentration as methacrylate radicals. The initial total radical concentration was lower and decreased to zero by 0°C. on warming. No polymer was obtained.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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