Improved Intrinsic Thermal Conductivity of Highly Crystalline Polyimide Films by Regulating Aggregation Structures

Polyimide (PI) films are limited by the low intrinsic thermal conductivity (λ) during their application in flexible electronics. This work proposes a strategy to enhance the intrinsic λ of PI by regulating the aggregation structure. Highly crystalline PI films with improved intrinsic λ are synthesized by optimizing the molar ratio of 4,4-oxydiphthalic anhydride (ODPA) to pyromellitic dianhydride (PMDA). At an ODPA to PMDA molar ratio of 1:9, the PI film crystallizes from solution and further develops during thermal imidization, exhibiting uniform spherulite distribution with the crystallinity up to 35.8%, 5.4 times higher than that of conventional PI films (5.6%). The in-plane λ (λ_∥) and through-plane λ (λ_⊥) of the highly crystalline PI film reach 2.58 and 0.18 W/(m·K), respectively, significantly higher than those of conventional low-crystallinity PI films (1.65 and 0.09 W/(m·K)). The highly crystalline PI film also exhibits excellent mechanical properties, demonstrating great potential for advanced flexible electronics.