Ultralarge Curvature Folding Resistance of Polyimide Films Based on Spring-Like Folding Segments

With the trend toward lighter andthinner flexible electronics,developing foldable polymeric substrates that can withstand ultralowfolding radiuses has become an urgent issue. Here, a strategy to developpolyimide (PI) films with excellent dynamic and static folding resistanceunder an ultralarge curvature through copolymerizing one unidirectionaldiamine with classic PMDA-ODA PIs to achieve a kind of folding-chainPI (FPI). It was theoretically and experimentally confirmed that thespring-like folding structure equipped PI films with an enhanced elasticbehavior and thus an excellent ability to endure a large curvature.Among them, FPI-20 did not show any crease even after folding over200000 times under a folding radius of 0.5 mm, while creases wereobserved on pure PI film only after folding 1000 times. It is noteworthythat the folding radius was almost 5 times smaller than that in currentreports (2-3 mm). Meanwhile, the spread angle of FPI-20 filmsafter static folding at 80 degrees C under a 0.5 mm folding radius get51% larger than that of films, showing the remarkable static foldingresistance.

Automated summary

This study presents a strategy to develop foldable polyimide (PI) films with excellent dynamic and static folding resistance. The newly developed folding-chain PI (FPI) films show enhanced elastic behavior and can endure a large curvature without any crease. FPI-20 film, for example, can withstand over 200,000 folds with a folding radius of 0.5 mm, while pure PI film shows creases after only 1,000 folds. This research is of great significance for the development of lighter and thinner flexible electronics.