| Abstract
| - A means of generating foams of high-temperaturepolymers, polyimides, has been developedfor use in dielectric layers in microelectronics. In thesesystems, the pore sizes generatedare in the tens of nanometers range, thus the term “nanofoams”.The foams are generatedby preparing phase-separated block copolymers with the majority phasecomprised ofpolyimide and the minor phase consisting of a thermally labile block.Films are cast, solventis removed, and the copolymers are cured, causing phase separation ofthe two blocks. Thelabile blocks are subsequently removed via thermal treatments leavingpores having a sizeand shape commensurate with the size and shape of the originalcopolymer morphology.The polyimide derived from pyromellitic dianhydride (PMDA) and2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF) was used as the matrixmaterials for the generation of nanofoams, and poly(propylene oxide) oligomers were used asthe thermally labileconstituent. The synthesis and characterization of the copolymerswere performed, and theprocess for obtaining nanofoams was optimized. The foams werecharacterized by a varietyof techniques including TEM, SAXS, WAXD, DMTA, density, and refractiveindex measurements. Thin-film, high-modulus foams with good mechanicalproperties can be synthesizedusing the copolymer/nanofoam approach.
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