High optical transparency and low dielectric constant of novel soluble polyimides containing fluorine and trifluoromethyl groups

A novel aromatic diamine containing fluorine and trifluoromethyl groups, alpha-bis(4-amino-3,5-difluorophenyl)-4-(trifluoromethyl)phenylmethane (1), was synthesized. Based on diamine 1 and four aromatic dianhydrides, a series of polyimides (PI) with high fluorine content were prepared via a one-step high-temperature polycondensation procedure. These obtained PIs were readily soluble in a variety of organic solvents, and they could afford flexible and strong films with low dielectric constants (2.57-2.84 at 1 MHz) and low moisture absorptions (0.23-0.45%). Thin films of these PIs exhibited high optical transparency and light color, with the cutoff wavelength at 311-354 nm and transmittance higher than 83% at 450 nm. Moreover, these PIs possessed eminent thermal stability and good mechanical properties.