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 °C. The low-temperature subglass relaxations, ranging from 150 to 200 °C, are typical β relaxations for standard polyimides. The relatively high-temperature β 1 subglass relaxations in polyimides 8 occur at a markedly higher temperature, i.e., approximately 300 °C, than typically observed in most other polyimides. The characteristic β 1 relaxation is associated with a step decrease in G‘ and small transition peaks appearing in tan δ and G ‘‘. Moreover, the insensitivity of the β 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 °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 FeCl 3 and AlBr 3, respectively.