ISSN:
0098-1273
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
It has been reported in earlier papers that aromatic additives can reduce the rate of radiation-induced degradation of poly(methyl methacrylate) (PMMA), depending on the concentration, the distribution, and the resonance of the aromatic system. In the present work, the temperature dependence is studied, together with the influence of molecular mobility, which is determined by the physical state of the system. For this purpose, PMMA containing benzene, biphenyl, naphthalene, anthracene, phenanthrene, pyrene, or benz[a]anthracene, was γ-irradiated at room temperature and also, except with naphthalene and biphenyl, in the temperature range -80 to 160°C. The changes in degradation rate were related to the first excited singlet state and to the resonance energy of the additives. The results suggest that at low temperatures both electron scavenging and transfer of excitation energy occur. At temperatures between the γ transition and the glass transition, the significance of energy transfer compared with electron scavenging increases, whereas the inhibitory effect decreases. Above the glass transition temperature the inhibition decreases more rapidly. This is related to scavenging of radical chain fragments, due to increasing molecular mobility, which causes a decrease in recombination rate. This sensitization of degradation competes with the inhibition by energy transfer and electron scavening, and may prevail at temperatures above 185°C. The opposing effects of these mechanisms can be clearly shown with the system PMMA-benzene. In viscous mixtures, sensitization prevails even at room temperature.
Zusätzliches Material:
8 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1974.180120116
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