Low dielectric constants of soluble polyimides derived from the novel 4,9-bis[4-(4-aminophenoxy)phenyl]diamantane

New diamantane-based polyimides are synthesized by reacting of 4,9-bis[4-(4-aminophenoxy)phenyl]diamantane with various aromatic tetracarboxylic dianhydrides. Films of these polyimides have low dielectric constants, ranging from 2.58 to 2.74, and low moisture absorptions less than 0.3%. Four of these films have good solubilities. Three nonfluorinated polyimides were soluble in o-chlorophenol, m-cresol, N-methyl-2-pyrrolidone (NMP), and chloroform. The hexafluoroisopropylidene-containing polyimide was soluble in m-cresol, chloroform, and tetrahydrofuran (THF). The soluble polyimides have molecular weights (M-n) ranging from 33 000 to 96 000. All polyimides formed tough transparent films, with tensile strengths of 55.3-101.4 MPa, elongations to break of 6.1-22.3%, and initial moduli of 1.9-2.2 GPa. Dynamic mechanical analysis (DMA) reveals that diamantane based polyimides have two transitions on the temperature scale between 0 and 400 degrees C. Their glass relaxations, characterized by DMA, occur at high temperatures, ranging from 296 to 413 degrees C. New diamantane-based polyimides are highly promising for electronic applications owing to their excellent physical properties, in particular an extremely low dielectric constant.