In Situ Preparation of Siloxane-Linked Colorless Polyimides with Low Dielectric Constant

Developing colorless polyimides with low dielectric constants is of great significance for display application. Herein, two siloxane-linked imide monomers with different functionalities of trifluorovinyl ether (TFVE) substituents were designed and synthesized. The obtained imide monomers could be easily converted into polyimides in situ through direct thermal [2 + 2] reactions between TFVE groups. Linear and cross-linked polyimides with perfluorocyclobutyl (PFCB) linkers were obtained via bulk polymerization, without any release of volatiles. Due to the introduction of siloxane and fluorinated PFCB linkers, the polyimides showed excellent transparency, hydrophobicity, and low dielectric constants. Transmittances of the prepared polyimide sheets with a thickness of about 2 mm were up to 72% at 450 nm. Dielectric constants were lower than 2.8 under an ultrahigh frequency of 20 GHz. The PFCB functionalized polyimides also showed high hydrophobicity with ultralow water absorption of 0.07% and water contact angles of about 100°. Furthermore, the thermal stability of polyimides could be highly improved by increasing the cross-linking density of polyimides. The cross-linked polyimide exhibited a 5% weight loss temperature of 529 °C and a glass transition temperature of 207 °C. This contribution provided an alternative approach to produce colorless and low-dielectric polyimides.