A Mechanistic Investigation of the Effect of Stress on the Photochemical Degradation of Polymers

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

Studies have shown that stress will accelerate the photochemical degradation of many polymers, but reasons for the increased degradation rates are not well understood. The primary objectives of this study are to determine the mechanistic origins of the stress-induced rate increases and to find a general expression for quantitatively relating stress to photodegradation rates. In order to circumvent the problems associated with the mechanistic complexities of photogradation and to facilitate rapid experimental progress, three key experimental strategies will be used. First, to simplify the mechanistically complicated degradation pathways of typical polymers, is proposed to study polymers containing metal-metal bonds placed periodically along their backbones. These polymers photodegrade by a straightforward mechanism with no unwanted side-reactions. Second, to eliminate the complexities caused by rate-limiting oxygen diffusion, radical traps will be built-in along the polymer backbones. Third, a computer controlled apparatus will be used to collect photdegradation quantum yields as a function of stress applied to polymer films. The data will be compared to the predictions of three degradation hypotheses: (1) the Plotnikov hypothesis, (2) the "Decreased Radical Recombination Efficiency" hypothesis (a theory that relates degradation rates the decreased ability of radical to recombine under the influence of stress), and (3) a photochemical analog of the Zhurkov equation. %%% This work may be of considerable practical significance because polymers are increasingly being used in structural applications, by which they are subjected to stress and light. A proper understanding of the synergy between light and stress is therefore essential for the accurate estimation of polymer lifetimes and for the development of stabilizing systems. Important fundamental principles about radical recombination in the solid state should also emerge from this study.