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 degrees C, are typical beta relaxations for standard polyimides. Another high-temperature beta(1) subglass relaxation occurs at a substantially high temperature of approximately 300 degrees C. The characteristic of beta(1) relaxation is associated with a step decrease in G' and small transition peaks in tan delta and G ". Their glass relaxations occur at extremely high temperature exceeding 500 degrees C. Their temperatures at a 5% weight loss ranges from 491 to 536 degrees C in air and from 518 to 566 degrees C in N-2 atmosphere.