HIGH-TEMPERATURE POLYMER NANOFOAMS BASED ON AMORPHOUS, HIGH T-G POLYIMIDES

A means of generating high temperature polymer foams which leads to po re sizes in the nanometre regime has been developed. Foams were prepar ed by casting block copolymers comprising a thermally stable block and a thermally labile material, such that the morphology consists of a m atrix of the thermally stable material with the thermally labile mater ial as the dispersed phase. Upon thermal treatment, the thermally unst able block undergoes thermolysis leaving pores of which the size and s hape art dictated by the initial copolymer morphology. Triblock and gr aft copolymers comprising high glass transition temperature amorphous polyimide matrices with poly(propylene oxide), as the thermally decomp osable coblock, were prepared. The copolymer synthesis was carried out through either the poly(amic alkyl ester) or poly(amic acid) precurso r and subsequent cyclodehydration to the polyimide by either thermal o r chemical means, respectively. Microphase-separated morphologies were observed for all copolymers, irrespective of the block lengths survey ed, by dynamic mechanical analysis. Upon decomposition of the thermall y labile coblock, a 5-15% reduction in density was observed, consisten t with the generation of a foam.