Synthesis and properties of low-dielectric-constant polyimides with introduced reactive fluorine polyhedral oligomeric silsesquioxanes

A high-performance, low-dielectric-constant polyimide (PI) nanocomposite from poly(amic acid) (PAA) cured with a reactive fluorine polyhedral oligomeric silsesquioxane (POSS) isomer was successfully synthesized. The features of this reactive fluorine POSS isomer [octakis(dimethylsiloxyhexafluoropropylglycidyl ether)silsesquioxane (OFG)] provided two important approaches (containing fluorine or being porous in the polymer matrix) of reducing the dielectric constant of PI. This reactive POSS isomer had an average of four epoxy groups and four fluorine groups on the POSS cage, and the epoxy groups could be cured with PAA to form a network framework of a PI/POSS nanocomposite. The PI/OFG nanocomposite had a high crosslinking density, high porosity (24.3%), high hydrophobicity, and low polarizability. These properties enhanced the thermal (glass-transition temperature similar to 362 degrees C) and dielectric (dielectric constant similar to 2.30) properties of PI more than other POSS derivatives introduced into the PI backbone. A large number of small POSS particles (< 10 nm) were embedded inside the PI matrix when the OFG content was low, whereas interconnected POSS aggregation domains were observed when the OFG content was high. (c) 2006 Wiley Periodicals, Inc.