A series of novel ultralow dielectric porous polyimide (PI) films containing adamantane groups was prepared via the thermolysis of polyethylene glycol (PEG) oligomers mixed into PI matrix. Scanning electron microscopy results indicated that the porous PI films showed closed pores with an average diameter of 120 ± 10 nm. Good thermal properties with 5% weight loss temperature of 499 °C in air atmosphere and glass transition temperature in excess of 310 °C were shown for porous PI films. Notably, the ultralow dielectric constant of porous PI films with 1.85 at 1 MHz was obtained and revealed via broadband dielectric spectroscopy. The effects of the chemical structure of the PI matrix and PEG content on the decomposition behavior of PEG and the performance of porous films were investigated. Wide‐angle X‐ray diffraction results indicated that the PI matrix with large d‐spacing generated weaker interactions between the PEG and PI backbone than those of PI matrix with small d‐spacing. As a result, the PEG for the PI matrix with large d‐spacing was completely decomposed. As indicated by the broadband dielectric spectroscopy results, lower dielectric porous PI films were prepared when the PEG contents in the PI matrix increased from 0 to 20 wt %. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 549–559

A system is designed to study the properties of nanofoams as well as interactions between the matrix and decomposition products of thermal labile content. With the increase thermal labile content, the dielectric constants of PI nanofoams decrease.

This study aimed to prepare porous polyimide (PI) films with an 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 T 5% (temperature of 5% weight loss) of 411 °C in air and T g (glass-transition temperature) of 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 lower polarizability, and the bulky adamantane groups and nanopores simultaneously provided enhanced free volumes. Moreover, the hydrophobicity of the adamantane groups and PDMS segments in PI induced substantial water resistance with the lowest water absorption of 1.15%. These properties indicated the high potential applications of porous PI films as interlevel insulation materials in next-generation microelectronic devices.