Design of star-shaped trimeric UV absorbers with outstanding thermal and photostability for UV-resistant colorless polyimide film

Abstract

Colorless polyimide (CPI) has emerged as a promising material for flexible displays owing to its remarkable thermal stability and material flexibility. Nevertheless, CPI is susceptible to photodegradation induced by UV radiation, which requires effective mitigation strategies. Specifically, polymerization to form CPI necessitates high-temperature treatment and is predominantly used in high-temperature processes, thus emphasizing the need for additives with superior thermal stability to mitigate CPI photodegradation. In this study, we investigated the molecular structure-dependent stabilities and optical properties of trimer-type UV absorbers intended for CPI application. By substituting hydroxyphenyl benzotriazole (HBT) in various arrangements on a central linker, we synthesized three UV absorbers: 1,3,5-TPBT, 1,2,4-TPBT, and 1,2,3-TPBT. UV/VIS spectroscopy, computational calculation, solubility tests, thermogravimetric analysis, and TGA-GC/MS were used for characterization. Among the synthesized UV absorbers, 1,2,3-TPBT maintains the transparency of CPI films due to its low absorption in the visible light region. The high photostability of this UV absorber effectively mitigates the photodegradation of CPI films exposed to prolonged UV irradiation. This study suggests novel molecular design strategies to develop highly photo- and thermal-stable trimeric UV absorbers for UV-resistant CPI films.