中文摘要：

以N，N-二甲基乙酰胺（DMAc）为溶剂，在聚氨酯（PU）溶液中使均苯四酸二酐（PMDA）与4，4’-二氨基二苯醚（4，4＇-ODA）缩聚成聚酰亚胺（PI）预聚体——聚酰胺酸（PAA），从而制成PAA／PU的混合溶液，然后刮涂成膜，经过热处理使得PAA亚胺化和Pu降解，制备多孔PI薄膜．通过对薄膜进行红外光谱、热失重分析及透射电镜（TEM）观察，结果表明，最佳的Pu热降解温度为360℃，PU降解后在PI基体中留下长条状纳米孔，且孔径大小随聚氨酯含量的增加而增大．通过对薄膜进行力学性能、介电性能和吸水率研究，结果表明，随着体系中PU用量的增加，热处理后的多孔PI薄膜的介电常数逐渐下降，但拉伸强度降低，吸水率上升、

英文摘要：

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.