Imide Ring Electron Density Modulation Enabling Rational Design of Atomic Oxygen-Resistant Polyimides

Abstract

Resistance to atomic oxygen (AO) erosion is a critical prerequisite for polymeric materials in low Earth orbit applications, yet understanding its erosion mechanisms and designing materials with superior AO resistance remain formidable challenges. Herein, we propose a rational design strategy that modulates the electron density of imide rings through conjugated benzene structures to enhance polyimide’s AO resistance, which is systematically validated through combined theoretical calculations and experiments. Theoretical analysis indicates that electrophilic AO preferentially targets the electron-rich moieties within the polymer chain, specifically the benzene and imide rings. AO attack on the former typically yields chemically stable C–O species (e.g., epoxides or phenols) without immediate chain scission; in sharp contrast, oxidative assault on the latter triggers catastrophic ring-opening and decarboxylation (CO2 release), precipitating irreversible backbone disintegration. Guided by this insight, we introduce conjugated benzene structures to delocalize the electron density of the imide rings, thereby mitigating electrophilic AO attack and enhancing polyimide’s AO resistance, as further verified by DFT calculations and Molecular Dynamics (MD) simulations. Subsequently, four distinct polyimides are synthesized and subjected to ground-based AO exposure tests at a fluence of 1.08 × 1020 atoms/cm2. The experimental results show that the modified polyimides significantly outperform the reference (PMDA-ODA) in surface morphology retention and mass stability, corroborating the theoretical predictions. Notably, the benzophenone-modified PI achieves exceptional resistance with a postexposure roughness (Ra) of only 25.6 nm and an erosion yield as low as 2.06 × 10–24 cm3/atom, representing a 30% reduction relative to the reference. This work demonstrates that modulating imide ring electron density is a decisive pathway for enhancing AO resistance, providing vital theoretical guidance for the development of advanced space-grade polyimides.