EXAFS study of structural changes in Zr-doped polyimides

Abstract

Surfaces of spacecraft in low-earth orbit experience severe erosion by extremely reactive species, such as atomic oxygen (AO). Primary structural materials in spacecraft flight include durable polymer polyimides. To attempt to improve resistance to AO attack, polyimide chemical precursors based on PMDA-ODA polyamic acid have been synthesized with the goal of appending zirconium components onto the main chain, in the hope that initial AO attack would form a protective ZrO2 layer which would inhibit further erosion. The precursor and fully cured polymer are both structurally disordered and cannot be studied by standard x-ray diffraction. We have therefore used extended x-ray absorption fine structure (EXAFS) to examine the zirconium near-neighbor environment in the Zr-containing precursors as a function of curing temperature, in order to look for possible changes in the Zr environment as the polyimide is formed. The results appear to show the formation of ZrO2 upon imidization, consistent with the protective-layer model.