Synthesis and characterization of high Tg nanofoams based on pyromellitic dianhydride and 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane polyimide block and graft copolymers

Abstract

Thermally stable polyimide block and graft copolymers with labile con1ponents (especially polypropylene oxide), have been prepared and investigated as low dielectric materials that afford desirable thermal, mechanical and electrical properties. Polyimide nanofoams based upon the controlled pyrolysis of the labile component were prepared. The methodology for producing the nanofoams was to first spin cast well-designed microphase separated graft or block copolymer solutions comprised of the thermally stable 1, I-Bis( 4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3FDA)/pyromellitic dianhydride (PMDA) based polyimide main chain and polypropylene oxide based thermally labile graft of block copolymers. The thermally stable material was designed to be the continuous phase, and the unstable moiety served as the dispersed phase so that closed cell structures could be obtained. Upon thermal treatment under inert atmosphere, the materials can be spun cast and cured in place, if so desired. However, if the polymers are exposed to the oxygen atmosphere, the unstable component can be selectively degraded, generating micropores that are related to the size of the initial microphase separated copolymer morphology.