Nonfluorinated copolymerized polyimide thin films with ultralow dielectric constants

A series of copolymerized polyimide (PI) thin films with low dielectric constants were prepared with different molars ratio of bis[3,5‐dimethyl‐4‐(4‐aminophenoxy)phenyl]methane and 9,9‐bis[4‐(4‐aminophenoxy)phenyl]fluorene as diamines and 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride) as a dianhydride. Some films possessed good dielectric properties with an ultralow dielectric constant of 2.3 at 1 MHz. The structures and properties of the thin films were measured with Fourier transform infrared and NMR spectroscopy, thermogravimetric analysis, and dynamic mechanical analysis. The PI films exhibited glass‐transition temperatures in the range 223–243°C and possessed initial thermal decomposition temperatures reaching up to 475–486°C in air and 464–477°C in nitrogen. All of the PI films exhibited excellent solubility in organic solvents. The mechanical properties of these films were also examined.