Soluble Polyimides Containing Bulky Rigid Terphenyl Groups with Low Dielectric Constant and High Thermal Stability

An aromatic diamine monomer containing an asymmetric pendant terphenyl group, 3,5-(diphenyl)phenyl-2,4-diaminobenzene, was synthesized based on a two-step reaction. The monomer was further reacted with three different commercial aromatic dianhydrides (3,3′,4,4′-biphenyltetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride) in one-step high-temperature polycondensation to prepare a series of soluble polyimides: PI 3a–3c . The chemical structure of the obtained monomer and polymers was characterized carefully, and some selective properties were investigated in detail. These polyimides exhibit excellent thermal stability and low dielectric constant and water absorption. Their glass transition temperatures ( T g ) and 10% weight loss temperatures (T 10% ) in N 2 are up to 337°C and 596°C, respectively. Their dielectric constant and water absorption are 2.64 (at 1 MHz) and 0.73%, respectively. Moreover, the polyimides also have high optical transparency. Their values are in the range of 67–81% at a wavelength of 450 nm, and the cut-off wavelengths are in the range of 343–359 nm. Graphic Abstract