Synthesis of space-grade polyimides using bio-based sustainable chemistry

Polyimides (PIs) with imide and aromatic rings are widely used polymers in the space field. They possess outstanding properties such as excellent thermo-chemical stability and mechanical strength, which, combined with their light weight, make them ideal candidates for the realization of structures in space extreme environment. The synthesis of these materials is traditionally done using solvents (dimethyl acetamide, n-methyl pyrrolidone, tetrahydrofuran), that are toxic to workers and the environment. An advantage of our chemical strategy is to overcome the use of these solvents, by using greener alternatives, such as the bio-based dimethyl isosorbide (DMI). In this work, we focus on the molecular design and synthesis of polyimides with advanced properties for space applications, including for example the fabrication of lightweight self-healing materials for extra-terrestrial habitats. Polyimides are synthetized in two steps, using dimethyl isosorbide (DMI), a non-toxic and bio-based solvent already used in our past work [1, 2]. First, aromatic dianhydride was added to a mechanically stirred solution of aromatic diamine in DMI. Then, poly(amic acid) (PAA) is converted to polyimide by thermal or chemical imidization. Selected additives, such as boric acid, are added during the synthesis to enhance the intrinsic self-repair ability. The dynamicity and reversibility of the chemical bonds, which is crucial for self-healing, are analysed by FTIR spectroscopy. Indeed, intrinsic self-healing is based on the mobility of chains. In addition, the ATR-FTIR spectra confirmed the presence of additives embedded in the polymer matrix. Further characterizations include measurement of the density of the polyimide-based materials by the hydrostatic weighing method, considering the guidelines of the ASTM D792 standard, and assessment of the thermal stability in a wide temperature range by differential scanning calorimetry (DSC).