A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane (PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the decrease of tensile strength and the rise of water absorption.

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 degrees C, upon a thermal treatment the PU undergoes 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.

A method to generate nanoporous polyimide films with low dielectric constants was proposed. The preparation consisted of two steps. Firstly, a polyimide/silica hybrid film was prepared via sol–gel process. Secondly, the hybrid film was treated with hydrofluoric acid to remove the dispersed silica particles, leaving pores with diameters between 20 and 120 nm, depending on the size of silica particles. Both hybrid and porous films were subjected to a variety of characterizations including transmission electron microscopy observation, dielectric constant measurement and tensile strength measurement.

采用溶胶-凝胶法(Sol-Gel)制备了二氧化硅不同质量分数的聚酰亚胺/二氧化硅(PI/SiO2)纳米复合薄膜.并用TEM、力学性能、吸水性能及介电性能测试等方法研究了薄膜的结构与性能.结果表明,SiO2微粒均匀分散在PI基体中,粒径随着SiO2含量的增加而增大;当SiO2质量分数在20%以内时对PI基体有增强作用,且在10%左右拉伸强度达到最大,而吸水率逐渐减小,介电常数则变化不大.