About the Ageing-Induced Modifications of Physical-Chemical and Electrical Properties of Polyimide (PMDA-ODA) Under Gamma Radiation and High Temperatures

This study investigates the effects of radiation-induced ageing on the physical, chemical, mechanical and electrical properties of Poly[4,4′-oxydiphenylene- pyromellitimide] (PMDA-ODA) polyimide, a high-performance insulation material widely used in aerospace applications. Using a combination of Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and dielectric spectroscopy, the degradation mechanisms were systematically analysed under varying radiation dose rates and thermal conditions. Results reveal a dual-path degradation process: at lower dose rates (< 860 Gy/h), microstructural modifications, such as chain scission predominate, under more severe conditions (∼2 kGy/h and 70°C), oxidation becomes the dominant mechanism. Despite these changes, TGA confirms exceptional thermal stability with almost invariant residual mass at 800°C (∼60%) and mechanical testing shows increased stiffness with ageing, attributed to chain crosslinking. Dielectric analysis indicates an increase in permittivity, dissipation factor and DC conductivity with ageing severity, whereas AC breakdown voltage remains largely unaffected. These findings highlight the complex interplay between molecular degradation and macroscopic performance, providing a basis for the nondestructive evaluation and reliable deployment of PMDA-ODA in extreme environments.