Effect of electron beam radiolysis on mechanical properties of high performance polyimides. A comparative study of transparent polymer films

The mechanical properties of four optically transparent polyimides prepared from the dianhydrides ODPA and 6FDA and the diamines ODA and DAB were assessed. The property changes when these polymers are subjected to high-energy electron-beam irradiation (1 MeV) for doses up to 18.5 MGy and temperatures up to 523 K were also studied and compared. The corresponding changes on radiolysis of Kapton are reported for comparison with the other polymers. The tensile properties of the four polyimides differed mainly by the nature of the dianhydride, with the ODPA polymers undergoing necking and cold drawing and the 6FDA polymers brittle fracture. The four polyimides were synthesized with the objective of obtaining optimum transparency for space applications where high-energy radiation doses of 15-20 MGy may be expected in geosynchronous orbits over a life span of 20 years. The polyimides were shown to maintain good optical and tensile properties at temperatures up to about 450 K for a dose of 18.5 MGy, but above this temperature the moduli of the polymers began to deteriorate and there was a small decrease in the transmittance of the exposed polymer films.