Flexible Polydimethylsiloxane-Based Porous PolyimideFilms with an Ultralow Dielectric Constant and Remarkable Water Resistance

This study aimed to prepare porous polyimide (PI) films with ultralow dielectric constant and low water absorption by incorporating flexible polydimethylsiloxane (PDMS) segments and rigid adamantane groups into PI chains. Nanopores were then introduced by thermolysis of the thermally labile polyethylene glycol added into PI resin. Scanning electron micrographs showed that the porous PI films had uniform nanopores, which were regularly shaped with an average diameter of 237 ± 19 nm. The porous PI films further exhibited good thermal properties with T5% of 411 °C in air and Tg (299–301 °C) because of the enhanced rigidity provided by adamantane. Outstanding dielectric properties and the dielectric constant value of 1.85 at 1 MHz were achieved for the films. The adamantane groups and PDMS segments have contributed to the lowered polarizability, and the bulky adamantane groups and nanopores simultaneously provided enhanced free volumes. Moreover, the hydrophobicity of the adamantane groups and PDMS segments i...