Microscopic decomposition mechanism and property calculation of high-nitrile polyimide based on ReaxFF molecular dynamics simulation

The modification of polymer molecules with polar groups can greatly improve the dielectric constant of polymer materials and thus improve the energy storage density of polymer-based energy storage dielectric materials . In this paper, cyanide groups (–C≡N) with high polarity were introduced into different types of polyimide (PI) molecules to obtain 4 kinds of high-nitrile PI models based on a reactive force field (ReaxFF). The dielectric constant, glass-transition temperature and O2/H2O diffusion coefficient in different systems were calculated. The ageing degradation mechanism of high-nitrile PI under high temperatures and intense electric fields was studied at the atomic level. The results showed that the dielectric constants of high-nitrile PI were significantly improved compared to those of Kapton PI. Meanwhile, high-nitrile PI obtained better electric-ageing-resistance ability and could better inhibit the diffusion of the small molecules (O2, H2O, etc.) that accelerate dielectric material ageing to a rate faster than that of Kapton PI. The cyanide group reduced the thermal stability of high-nitrile PI to a level lower than that of Kapton PI. However, most high-nitrile PI could still meet the requirements of high-temperature operations (over 200 °C), indicating that high-nitrile PI is an ideal material for high-temperature energy storage applications . • Cyanide groups were introduced into different types of polyimide molecules to obtain polymer with high dielectric constant. • The free diffusion of small molecules such as H 2 O and O 2 in the material were hindered in high-nitrile polyimide models. • High-nitrile polyimide showed better agglomeration under an intense electric field than pure Kapton polyimide did. • The product distribution and microscopic mechanism of high-nitrile polyimide degradation were revealed at the atomic level.