Study on preparation and dielectric properties of cellular polyimide films

To explore low dielectric polyimide,cellular polyimide films were prepared from pyromellitic dianhydride and 4,4′-diaminodiphenyl ether via a combined technique of solution induced phase separation and thermal imidization.These polyimide films displayed good thermal stability.SEM analyses showed that the obtained polyimide films had various cellular structures with the different conditions,such as the composition and temperature of coagulation bath,staying time,etc.The films with sponge-like cellular structures exhibited lower dielectric constants than those with finger-like structures.When the film was prepared in the conditions the coagulation bath of DMAc/H2O of 20/80,the temperature of 25℃ and the staying time of 20min,the film was full of sponge-like structure and its dielectric constant was low to 1.45.