Abstract:

A new route to porous polyimide films which leads to pore sizes in the nanometer regime was  developed. The polyimide foams were prepared from blending PAA and PU via in situ polymerization(the latter being the disperse phase) by the thermolysis of PU and imidization of PAA, so porous polyimide(PI) films were prepared. The results of  IR, TGA and TEM measurement shows that the optimal thermolysis temperature of PU is 360 ℃, upon a thermal treatment the PU undergoes thermal decomposition, leaving strip nanopores in PI matrix, and the size of pores increases with  increasing PU content. Because of the existence of nanopores, the dielectric constant of PI decreased by a wide margin and was less than 2.0 at PU mass fraction 20%, thus proving that this is an effective means to reduce the dielectric constant of PI, but it cause the decrease of tensile strength and the rise of water absorption.

Key words: Polyimide; Polyurethane; Porosity; Dielectric constant