ISSN:
0449-2978
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Isotactic and atactic poly(methyl methacrylate) containing varying amounts of polymerization initiator and chain-transfer additives, and carefully purified radiation-polymerized material, were γ-irradiated in the dark at liquid nitrogen temperature. On warming to room temperature at a near-linear rate of 20°K./min., a glow peak having a maximum luminescence intensity at 162 ± 8°K. was observed in all samples; an additional peak at 239 ± 7°K. was resolved relatively infrequently. Low luminescence yields precluded an investigation of the spectral distribution of the glow peaks. It is shown that the electron traps associated with the lower temperature peak are most probably the main-chain methyl groups, while the higher temperature glow peak is tentatively associated with escape of electrons from structural defects in a few small crystalline regions of the samples. It is postulated that, for the peak at 162°K., the trapped electrons combine radiatively with luminescence centers when thermally induced rotational motion of the main-chain methyl groups permits sufficient wave-function overlap. Assuming that methods of glow curve analysis proposed for inorganic materials are applicable to organics, first-order recombination kinetics and an activation energy of 0.084 ± 0.006 e. v. are deduced for the intensity maximum at 162°K. This activation energy is in fair agreement with that obtained by Bordoni et al. for an unspecified side-chain motion occurring at similar temperatures, but is only about half the values quoted with some reservations by Powles and by Kawai on the basis of NMR experiments. It was not possible to determine the kinetics of the 239°K. peak with certainty, but an activation energy of 0.432 ± 0.085 e. v. follows from a first-order assumption. The additives present in the samples did not appear to play any significant part as electrontrapping agents; this observation contrasts with some recent work on the visible and ultraviolet absorption spectra of the same materials which showed a close correlation of additional bands developed following irradiation with the presence of specific additives.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1968.160060707
Permalink
