Preparation and properties of pale‐colored and optically transparent fluoro‐containing polyimide films with low solar absorptivity and enhanced high‐temperature dimensional stability for potential applications in space environments

Abstract Two organo‐soluble polyimide (PI) resins were prepared from a tricyclic fluoro‐containing dianhydride 9,9‐bis(trifluoromethyl)xanthene‐2,3,6,7‐tetracarboxylic dianhydride (6FCDA) and aromatic diamine of 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane (BDAF) for PI‐II a and 1,3‐bis(3‐aminophenoxy)benzene (133APB) for PI‐II b , respectively. For comparison, two analogous PIs were prepared from 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and the same diamines to afford PI‐I a (6FDA‐BDAF) and PI‐I b (6FDA‐133APB), respectively. Incorporation of the rigid and planar xanthene units in the 6FCDA‐PIs obviously decreased the solubility of the resins in organic solvents. Flexible and tough PI films were fabricated from the PI solutions in N,N ‐dimethylacetamide (DMAc). The PI films derived from the rigid and planar 6FCDA dianhydride exhibited obviously enhance thermal stability, and high‐temperature dimensional stability. For example, PI‐II a (6FCDA‐BDAF) showed the glass transition temperature ( T g ) and coefficient of linear thermal expansion (CTE) values of 311.5°C and 50.5 × 10 −6 /K, respectively, which were all superior to those of the PI‐I a counterpart ( T g = 264.6°C; CTE = 55.4 × 10 −6 /K). In addition, the 6FCDA‐PI films maintained the intrinsically excellent optical transparency of the fluoro‐containing PI films and showed the comparable optical properties to those of the 6FDA‐PI films. As for the properties highly related to the space applications, all the PI films exhibited low solar absorptivity ( α ) values of 0.18–0.20 and the good thermal emissivity ( ε ) values in the range of 0.68–0.70. PI‐I a (6FDA‐BDAF) and PI‐II a (6FCDA‐BDAF) films showed the similar atomic oxygen erosion behaviors with the standard Kapton® type of PI film derived from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA).