High subglass transitions appearing in the rigid polyimides derived from the novel 1,6-bis(4-aminophenyl)diamantane

This work has synthesized new diamantane-based polyimides by reacting 1,6-bis(4-aminophenyl)diamantane (5) with various aromatic tetracarboxylic dianhydrides. Dynamic mechanical analysis (DMA) reveals that diamantane-based polyimides have three relaxations on the temperature scale between 0 and 500 degrees C. The low-temperature subglass relaxations, ranging from 150 to 200 degrees C, are typical beta relaxations for standard polyimides. The relatively high-temperature beta(1) subglass relaxations in polyimides 8 occur at a markedly higher temperature, i.e., approximately 300 degrees C, than typically observed in most other polyimides. The characteristic beta(1) relaxation is associated with a step decrease in G' and small transition peaks appearing in tan delta and G ". Moreover, the insensitivity of the beta(1) subglass relaxation temperature to changes in the dianhydride demonstrates that the subglass process is localized largely within the diamine moiety. Their glass relaxations occur at extremely high temperatures exceeding 500 degrees C. These films had low dielectric constants ranging from 2.54 to 2.74, as well as low moisture absorptions less than 0.40%. In addition, the polyimides 8d and 8e are soluble in o-chlorophenol, chloroform, N-dimethylacetamide (DMAc), and tetrahydrofuran (THF). These films have tensile strengths to break values up to 124 MPa, elongation to break values up to 5.6%, and initial moduli up to 2.3 GPa. Interestingly, selective functionalization of 1,6-dibromodiamantane to 1,6- and 4,9-diphenyldiamantanes is attained using the catalysts FeCl3 and AlBr3, respectively.