High Subglass Transition Temperatures and Low Dielectric Constants of Polyimides Derived from 4,9-Bis(4-aminophenyl)diamantane

This work synthesizes new diamantane-based polyimides by reacting 4,9-bis(4-aminophenyl)diamantane ( 4 ) with various aromatic tetracarboxylic dianhydrides. Poly(amic acid)s have high inherent viscosities of 0.74−1.36 dL/g. The polyimide 7 d can be soluble in o -chlorophenol, chloroform, and THF. Their cast films have a tensile strength at break up to 127 MPa, elongation to break up to 4.8%, and an initial modulus up to 2.3 GPa. These films have low dielectric constants ranging from 2.53 to 2.72, in addition to low moisture absorptions less than 0.33%. Dynamic mechanical analysis (DMA) reveals diamantane-based polyimides to have three relaxations over room temperature. The low-temperature subglass relaxations, ranging from 125 to 195 °C, are typical β relaxations for standard polyimides. Another high-temperature β 1 subglass relaxation occurs at a substantially high temperature of approximately 300 °C. The characteristic of β 1 relaxation is associated with a step decrease in G ‘ and small transition peaks in tan δ and G ‘‘. Their glass relaxations occur at extremely high temperature exceeding 500 °C. Their temperatures at a 5% weight loss ranges from 491 to 536 °C in air and from 518 to 566 °C in N 2 atmosphere.