Nanoporous polyimides derived from highly fluorinated polyimide/poly(propylene oxide) copolymers

Porous, low dielectric constant polyimide films have been made by a "nanofo am" approach. The pore sizes generated in the polymer films are in the tens of nanometers range, hence the term "nanofoams". The nanoporous foams are generated by preparing triblock copolymers with the majority phase comprisi ng polyimide and the minor phase consisting of a thermally labile block. Fi lms of the copolymers are cast and then heated to effect solvent removal an d annealing, resulting in microphase separation of the two dissimilar block s. The labile blocks are selectively removed via thermal treatments, leavin g pores the size and shape of the original copolymer morphology. The polyim ide derived from 2,2-bis(4-aminophenyl)hexafluoropropane (6FDAm) and 9,9-bi s(trifluoromethyl)xanthenetetracarboxyl dianhydride (6FXDA) was used as the matrix material for the generation of nanofoams, and specially functionali zed poly(propylene oxide) oligomers were used as the thermally labile const ituent. The synthesis and characterization of the copolymers were performed and the process for obtaining nanofoams was optimized. The foams were char acterized by a variety of techniques including thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA), density, small-angle X-ray scattering (SAXS), refractive i ndex, and dielectric constant measurements. Thin-film, high-modulus nanopor ous films with good mechanical properties and dielectric constants similar to2.3 have been synthesized by the copolymer/nanofoam approach.