POLYIMIDE NANOFOAMS BASED ON ORDERED POLYIMIDES DERIVED FROM POLY(AMIC ALKYL ESTERS) - PMDA 4-BDAF/

A means of generating foams of high-temperature polymers, polyimides, has been developed for use in dielectric layers in microelectronics. I n these systems, the pore sizes generated are in the tens of nanometer s range, thus the term ''nanofoams''. The foams are generated by prepa ring phase-separated block copolymers with the majority phase comprise d of polyimide and the minor phase consisting of a thermally labile bl ock. Films are cast, solvent is removed, and the copolymers are cured, causing phase separation of the two blocks. The labile blocks are sub sequently removed via thermal treatments leaving pores having a size a nd shape commensurate with the size and shape of the original copolyme r morphology. The polyimide derived from pyromellitic dianhydride (PMD A) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF) was used as the matrix materials for the generation of nanofoams, and pol y(propylene oxide) oligomers were used as the thermally labile constit uent. The synthesis and characterization of the copolymers were perfor med, and the process for obtaining nanofoams was optimized. The foams were characterized by a variety of techniques including TEM, SAXS, WAX D, DMTA, density, and refractive index measurements. Thin-film, high-m odulus foams with good mechanical properties can be synthesized using the copolymer/nanofoam approach.