TEMPERATURE DEPENDENCE OF THE ESR SPECTRUM OF IRRADIATED ORIENTED POLYETHYLENE
Temperature dependence of the ESR spectrum in irradiated polyethylene was studied using stretched specimens. Among the observed spectra the septet spectrum with doublet substructure is known to be due to an allyl type'' --CH/ sub 2/-CH-CH =CH-CH/sub 2-/ radical. Although the spectrum observed at 142 deg C is such a septet (splitting 21.3 G) with doublet substructure (splitting 5.5 G), it changes with temperature in a complicated way. Positions of the peaks are displaced, and their apparent number changes, while the spectrum below -180 deg C remains unchanged. Such changes were found completely reversible with temperature, and the magnitude of the over-all splitting as well as the outermost doublet remained constant. The analysis of this complicated temperature dependence was carried out on the assumption that the hyperfine coupling constant of the BETA protons changes with temperature, while that of the alpha protons remains constant. By choosing an appropriate set of coupling constants (A/sub BETA ) of BETA protons, the observed spectrum could be reproduced. From the spectrum at -180 deg C were deduced A/sub BETA /sub 1/ = 30 G and A/sub BETA / sub 2/ = 11 G. Such inequivalence of the coupling might suggest that the methylenic group in the allyl type'' radical should be twisted with respect to the nodal plane of the unpaired pi electron. As the temperature rises, a hindered oscillation of the methylenic group will take place between two equivalent twisted positions with respect to the same nodal plane. Such behaviors were interpreted using a theory of time-dependent phenomena and the activation energy was obtained to be 410 cal/mole, the frequency factor being 4.6 x 10/sup 8/ sec/sup -1/. (auth)
- Research Organization:
- Japanese Assn. for Radiation Research on Polymers, Neyagawa City, Osaka
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-16-032988
- OSTI ID:
- 4777988
- Journal Information:
- Journal of Chemical Physics (U.S.), Journal Name: Journal of Chemical Physics (U.S.) Vol. Vol: 37; ISSN JCPSA
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
Similar Records
ELECTRON SPIN RESONANCE STUDIES OF TRANSIENT ALKYL RADICALS
Free radicals in an Adamantane matrix. XI. Electron paramagnetic resonance study of conformations in the $beta$-halo-tert-butyl radicals