Date of Award

Spring 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Committee Director

Wynford Harries

Committee Member

James L. Cox, Jr.

Committee Member

Govind Khandelwal

Committee Member

Desmond Cook

Committee Member

Edward R. Long

Abstract

The effects of electron radiation on a polyetherimide (PEI), Ultem*, were investigated. In particular, the changes in the glass transition temperature (Tg) with absorbed radiation dose were studied. The polymer was exposed to mono-energetic beams of 100-keV electrons and 1.0-MeV electrons for doses up to 100 megagray (MGy). Dosimetry for the exposures was based on Monte-Carlo simulations of the transfer of energy from an energetic electron to the polymer and on comparison to Nylon standards. Dynamic mechanical analysis was used to determine the (Tg) for non-exposed PEI and the changes in (Tg) resulting from irradiation. The (Tg) did not change significantly for doses up to and including 75 MGy, while a significant increase in (Tg) occurred for a dose of 100 MGy. The cross-link and chain scission densities in the irradiated PEI were determined using infrared spectroscopy. The cross-link density increased with dose for all doses investigated. The chain scission density increased with dose for doses up to 75 MGy, but was lower for a dose of 100 MGy than for a dose of 75 MGy. Radical population kinetics, based in part on data from an electron paramagnetic resonance study, were correlated with the cross-link density and chain scission density to investigate the mechanism for the observed density variations with dose. The radical population simulations suggest that chain scissioning occurs less readily when the average radical separation during the exposure is less than three molecular radii. Finally, a model for the combined effects of cross-linking and chain scissioning is proposed which combines a statistical-mechanical model for the change in (Tg) with cross-link density and a free-volume model for the change in (Tg) with chain scission density.

DOI

10.25777/7msd-gz14

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