Structure-property relationships of low dielectric constant, nanoporous, thermally stable polyimides via grafting of poly(propylene glycol) oligomers

Abstract

Synthesis of high temperature polyimide foams with pore sizes in the nanometer range was developed. Foams were prepared by casting graft copolymers comprising a thermally stable block as the matrix and a thermally labile material as the dispersed phase. The copolyimides as the matrix material were prepared via polycondensation reactions of pyromellitic dianhydride with three new diamines (4BAP, 3BAP, and BAN) through the poly(amic acid) precursors. Functionalized poly(propylene glycol) (PPGBr-1000 and PPGBr-2500) as the labile oligomer was prepared via reaction of poly(propylene glycol) monobutyl ether with 2-bromoacetyl bromide. Graft copolymers were prepared by the reaction of the poly(amic acid)s with these thermally labile constituents. Upon thermal treatment the labile blocks were subsequently removed leaving pores with the size and shape of the original copolymer morphology. The polyimides and foamed polyimides were characterized y some conventional methods including FTIR, H-NMR, DSC, TGA, SEM, TEM, and dielectric constant. The average pore size of the polyimide nanofoams was in the range of 5-20 nm. The structure-property relationships of the prepared nanofoams were investigated based on the diamine structures and also molecular weights of labile groups. Copyright © 2008 John Wiley & Sons, Ltd.