The radiation of ULTEM

Polyimide polymers and membranes have interesting mechanical, thermal and electrical properties, and useful for industrial applications. They are also known for their exceptional thermo-oxidative and chemical resistance. High performance linear aromatic polymers with skeletons composed primarily of aromatic units are expected to be the materials used in high energy radiation fields, such as space and fusion reactor environments. In this study the ESR technique was employed to study the radiation resistivity of ULTEM. Gamma irradiations were carried out at 77 K and the ambient temperature. The neutral and anionic free radicals produced at 52 Mrad, and 77 K were further thermally annealed to just above glass transition temperature. The annealing resulted in two decay regions, namely 130-230 K and above 250 K, corresponding to the decay of anion radicals and neutral radicals respectively. The sample was further irradiated for 20 Mrads at 77 K. Photobleaching with visible light at 610 nm and 510 nm were carried out to detrap the anionic radicals. It was observed that up to 71% of the radicals were detrapped by photobleaching. Further annealing up to 490 K, following the photobleaching, showed complete decay of the radicals. 1H and 13C NMR of the polymers irradiated at 100, 250 and 500 Mrad clearly showed the evidence of cross linking at 250 Mrad. New peaks were identified for 1H NMR at δ 1.60 a 7.04. GPC results of the irradiated polymer at 52, 100, and 250 Mrad showed increase in molecular weight after initial decline