Low Dielectric Constants of Soluble Polyimides Based on Adamantane

This work synthesizes new adamantane-based polyimides by reacting 1,3-bis[4-(4-aminophenoxy)phenyl]adamantane ( 4 ) with various aromatic tetracarboxylic dianhydrides. The poly(amic acid)s have number-average molecular weights ( M n ) of 39 000−139 000. The M n 's of soluble polyimides 7 d and 7 e are 108 000 and 89 000, respectively. These films have low dielectric constants ranging from 2.77 to 2.91 and low moisture absorptions of less than 0.46%. Two of these polyimides have good solubilities, and even nonfluorinated polyimide 7 e can be soluble in chloroform. All polyimides 7 formed tough and transparent films. These films have tensile strengths of 88.2−113.5 MPa, elongations to break of 5.6−12.5%, and initial moduli of 2.0−2.2 GPa. Dynamic mechanical analysis (DMA) reveals that adamantane-based polyimides have two relaxations on the temperature scale between 0 and 350 °C. The subglass relaxations of polyimides 7 do not occur at the same temperature; instead, they range from 100 to 175 °C. Differential scanning calorimetry (DSC) and DMA reveal their glass transition temperatures ( T g 's) were found to be 232−330 and 262−343 °C, respectively. These T g 's lie in a manageable temperature range for processing in melt.