Intrinsically UV-Resistant Copolyimide: Exploring the Impact of UV-Absorbing Groups on Degradation and Comprehensive Performance

The rapid evolution of the aerospace industry has ignited an unprecedented surge in the demand for high-performance materials and their accompanying prerequisites. Polyimides (PIs), known for their outstanding comprehensive performance, have proven to be highly valuable as outer protective layers for spacecraft. However, prevailing PI materials still grapple with limitations including insufficient ultraviolet (UV) resistance, inadequate mechanical properties, suboptimal dimensional stability, and challenges in compatibility with other materials. Herein, this work fabricated new intrinsically UV-resistant PI films with greatly enhanced mechanical stability by copolymerization with a low-level introduction of ortho-hydroxybenzophenone diamine. The results show that the incorporation of UV-absorbing groups inhibits the ring-opening reactions of imide groups and promotes the formation of an inert surface during the UV degradation process. The copolyimides maintain excellent mechanical and thermal properties of the Upilex-S PI films and exhibit controllable coefficient of thermal expansion (CTE) values and surface free energy by regulating the molar ratio of diamines, which are significant factors for enhancing performance, compatibility, and durability of composite materials in diverse applications. This work endeavors to establish a relationship among chemical structure, degradation mechanism, and material performance. It provides a valuable foundation for the design of high-performance materials with enhanced UV resistance and comprehensive properties, as well as for the preparation of corresponding composite materials.